You hold a stick in your hands, one that you’ve just peed on. It foretells a future of sorts, for you. But the magic behind that stick is really all about a biochemical sandwich and a scientific test named ELISA. By Jeanne Garbarino, DXS Editor OH MY GOD OH MY GOD OH MY GOD OH MY GOD OH MY GOD OH MY GOD
Over and over again, that was all I could say. At the same time, I heard my husband on the other side of the bathroom door, in a very panicked voice asking, “Why are you saying oh my god? WHAY ARE YOU SAYING OH MY GOD?!?!”
Though, he really knew why.
The events immediately preceding our synchronous freak out session involved unwrapping a small plastic wand, removing its lilac cap, and subsequently inserting its absorbent tip into my stream of pee. Yes, folks, we are talking about the wand of destiny that is the pregnancy test.
Shortly after that lucky sperm cell unites with the prized product of the ovulatory process, theegg, a woman will immediately begin to experience changes required for growing another human inside of her body. One of the first detectable signs of pregnancy is a surge in a hormone called human chorionic gonadotropin or hCG.
Once the fertilized egg finds a cozy resting place in the wall of the uterus (a process termed implantation), the production of hCG is significantly ramped up. On average, implantation usually takes about 8-10 days for normal, healthy pregnancies. It is around this point on the baby growing timeline that home pregnancy tests can begin to detect the increased presence of hCG.
Chronologically speaking, we have sex, a sperm cell fertilizes an egg cell, said fertilized egg implants into uterus, our bodies up the production of hCG, and we pee on a stick to find out if all of these things really happened. But, exactly how do these little wands of destiny work?
The technology harnessed within the pregnancy test involves a biochemical assay called a “Sandwich ELISA” (ELISA= enzyme-linked immunoabsorbant assay, more on the “sandwich” part in a bit). The general function of an ELISA is to detect (and sometimes quantify) the presence of a substance in a liquid. In the case of a home pregnancy test, the substance is hCG and the liquid part is our urine.
Once pee is applied to the pregnancy test, it travels along the absorbent fibers, reaching defined areas that are coated with molecules, called “capture” antibodies, specifically designed to capture hCG. To help you visualize antibody science, picture a lacrosse stick, except the mesh pocket can only fit one specific type of ball:
Now, back to the sandwich part. On a home pregnancy test, there are three separate zones containing capture antibodies. Using their sharp wit and radical humor, scientists came up with “sandwich” to describe this sort of ELISA as they felt it was analogous to two slices of bread surrounding some delicious filling. Hilarious, right?
Ok, now that you’ve calmed down from laughing so hard, let us get back to the science. The first “slice of bread” is called the reaction zone, the “sandwich filling” is called the test zone, and the “last slice of bread” is called the control zone (see figure 2). Each of these zones is coated with capture antibodies, but differ from each other in how they work.
The antibodies on the reaction zone will capture only hCG and will detach from the strip upon exposure to urine. The test zone also contains capture antibodies that can only bind hCG, except they are securely attached to the absorbent strip, plus, there is an added dye. The control zone contains a general antibody (a lacrosse stick that will fit any ball) plus a dye, and serves to let the frantic user know that the test is functional.
As urine travels up the absorbent strip, it takes with it the reaction zone antibodies. If the urine is obtained from a pregnant woman, the reaction zone antibodies will be bound to hCG molecules found in the pee. When the pee solution reaches the test zone, there are two possible outcomes. If you are pregnant, the hCG/reaction zone antibody complexes will stick to the test zone antibodies and cause the dye to release (sometimes in a little “+” formation). If you are not pregnant, the reaction zone antibodies will just pass on through without saying hello.
The test culminates at the control zone, which is lined with general capture antibodies. Going back to picturing antibodies as lacrosse sticks, you will see that only the shape and size of the mesh pocket varies; the stick part is always the same. The general capture antibodies on the control zone will recognize and bind to the “stick” part of the reaction zone antibodies, and release a dye while doing so. This is how we know that the test worked correctly.
Biochemically speaking, the home pregnancy test is nothing but a soggy antibody sandwich that smells of urine. From a family planning standpoint, however, this technology can impact us in ways beyond belief. But, aside from the potential for the “are you pregnant” window to induce one into a hyperventilated state, the process happening within that handheld chemistry lab is actually quite impressive. In a matter of minutes, we can know if it is ok to go out and party with friends, or if it would be a better choice to stay in and begin to nest – all from the comfort of our own bathrooms. Three cheers for science!
For a cool animation showing how a pregnancy test works, go here. Visit WomensHealth.govfor more information about pregnancy tests. Planned Parenthoodoffers scientifically accurate information about women’s reproductive health. For blogs, check out this list on Babble, and this list on BlogHer.
Wilcox AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus and loss of pregnancy. N Engl J Med. (1999) Jun 10;340(23):1796-9.
There’s an old saying: You can’t be a little bit pregnant. Pregnancy is what you might call a binary condition – you either are with child, or you’re not. Home pregnancy tests embody this thinking. You pee on the end of a stick, and three minutes later you either do or do not see a line in the results window. Congratulations, you’re expecting!
Biologically, of course, things are a bit more complicated. Pregnancy tests check for the presence of a particular protein, human chorionicgonadotropin (hCG), that is also elevated in women with breast and ovarian cancers. As a result, it’s sometimes useful to be able to quantify the levels of hCG – or any other so-called “biomarker” – with a bit more precision. A new diagnostic device, developed by a team of Texas researchers and described in the journal Nature Communications, enables precisely that.
The team developed what’s called a microfluidic device, a circuit of tiny channels etched into glass (or sometimes plastic or a rubber polymer) that enable researchers to run chemical assays on tiny volumes of sample. That’s helpful when the sample is particularly precious or hard to come by – a drop of blood from a newborn baby, say.
Microfluidic devices, sometimes called “lab-on-a-chip” devices (because they resemble computer chips in both design and size), are popular in both drug development companies and research laboratories, as well as in the clinic. Their reduced volumes and size mean they use less reagent volumes (making them relatively inexpensive) and produce less waste. They are also faster and higher throughput than many traditional experiments, and are easily automated.
The downside is in the data output. To read the results of a microfluidic assay, researchers generally need some large and expensive piece of hardware that can, for instance, interrogate the chip with a laser to measure fluorescence intensity. That requirement isn’t a problem for most research labs, but it does reduce the likelihood that the technology can be adopted by your general practitioner. And it makes the development of microfluidics-based home tests, analogous to a home pregnancy kit, all but impossible.(*)
To circumvent these problems, the Texas team used a clever “SlipChip” design. A SlipChip is a microfluidic device formed by overlaying two glass plates, whose channels can form either of two flow paths depending on the position of the top plate relative to the bottom. In one configuration, the channels flow left-to-right; in the other (that is, after sliding or “slipping” the top plate), they flow bottom-to-top. Samples and reagents are loaded in one configuration, and the chip is “slipped” to start the readout process.
The SlipChip design
Source: Nat. Commun. 3:1283 doi: 10.1038/ncomms2292 (2012).
Here’s how the authors describe it:
In the SlipChip, two pieces of glass etched with microfluidic wells and channels are assembled together in the presence of mineral oil. A fluidic path is formed when the two plates aligned in a specific configuration. Samples or reagents are preloaded through drilled holes using a pipette, and the top plate is then moved relative to the bottom plate to enable the diffusion and reaction of samples or reagents.
The team calls its device a “volumetric bar-chart chip,” or V-Chip. The V-Chip runs what’s called an ELISA (enzyme linked immunosorbent assay), which is the gold standard in biomarker quantitation tests. Normally ELISAs are read with some sort of instrument that can measure either color, fluorescence, or chemiluminescence. The V-Chip is far simpler (albeit, less quantitative).
It uses an enzyme called catalase to degrade hydrogen peroxide into oxygen gas in volumes proportional to the molecule of interest – in this case, hCG. That gas, in turn, forces a column of red dye upwards to a height determined by the hCG concentration. (See the V-Chip in action here.) The result is a easy to read, microfluidic bar graph, with the height of each bar indicating not only if a woman is pregnant, but just how much hCG is in her urine. In a comparison against a commercial home pregnancy test, the V-Chip was more sensitive at low hCG concentrations, and more accurate at very high concentrations.
The V-Chip’s design is flexible, the authors note, and can be used to test either a large number of samples for a single molecule (as might be done in a clinical trial) or a single sample for multiple molecules, as in cancer screening. The current design allows as many as 50 parallel fluidic channels, meaning up to 50 molecules could be tested in parallel. In one experiment, the team used a six-channel design to test a panel of breast cancer cell lines for the abundance of three proteins (estrogen receptor, progesterone receptor, and human epidermal growth factor receptor) commonly found on breast cancer cells.
The simplicity of the test means it should be possible to design a device that can be used at home or in a doctor’s office. It is cheap, fast, and requires no special hardware. That means it could be used in areas lacking access to top-shelf medical care. It could even be used in the absence of a physician altogether. “The bar chart could be captured as an image using a smart phone, similar to a barcode reader and transmitted to a cloud computer for instant medical suggestions in the future,” the authors write. Now, how cool would that be?(*) That’s not entirely true. Harvard researcher George Whitesides has figured out a way to print microfluidic circuits onto paper, resulting in very simple and inexpensive designs. Boston-based Diagnostics For All is developing such tests for use in third world countries.
The four basic categories of molecules for building life are carbohydrates, lipids, proteins, and nucleic acids.
Carbohydrates serve many purposes, from energy to structure to chemical communication, as monomers or polymers.
Lipids, which are hydrophobic, also have different purposes, including energy storage, structure, and signaling.
Proteins, made of amino acids in up to four structural levels, are involved in just about every process of life.
The nucleic acids DNA and RNA consist of four nucleotide building blocks, and each has different purposes.
The longer version
Life is so diverse and unwieldy, it may surprise you to learn that we can break it down into four basic categories of molecules. Possibly even more implausible is the fact that two of these categories of large molecules themselves break down into a surprisingly small number of building blocks. The proteins that make up all of the living things on this planet and ensure their appropriate structure and smooth function consist of only 20 different kinds of building blocks. Nucleic acids, specifically DNA, are even more basic: only four different kinds of molecules provide the materials to build the countless different genetic codes that translate into all the different walking, swimming, crawling, oozing, and/or photosynthesizing organisms that populate the third rock from the Sun.
Big Molecules with Small Building Blocks
The functional groups, assembled into building blocks on backbones of carbon atoms, can be bonded together to yield large molecules that we classify into four basic categories. These molecules, in many different permutations, are the basis for the diversity that we see among living things. They can consist of thousands of atoms, but only a handful of different kinds of atoms form them. It’s like building apartment buildings using a small selection of different materials: bricks, mortar, iron, glass, and wood. Arranged in different ways, these few materials can yield a huge variety of structures.
We encountered functional groups and the SPHONC in Chapter 3. These components form the four categories of molecules of life. These Big Four biological molecules are carbohydrates, lipids, proteins, and nucleic acids. They can have many roles, from giving an organism structure to being involved in one of the millions of processes of living. Let’s meet each category individually and discover the basic roles of each in the structure and function of life.
You have met carbohydrates before, whether you know it or not. We refer to them casually as “sugars,” molecules made of carbon, hydrogen, and oxygen. A sugar molecule has a carbon backbone, usually five or six carbons in the ones we’ll discuss here, but it can be as few as three. Sugar molecules can link together in pairs or in chains or branching “trees,” either for structure or energy storage.
When you look on a nutrition label, you’ll see reference to “sugars.” That term includes carbohydrates that provide energy, which we get from breaking the chemical bonds in a sugar called glucose. The “sugars” on a nutrition label also include those that give structure to a plant, which we call fiber. Both are important nutrients for people.
Sugars serve many purposes. They give crunch to the cell walls of a plant or the exoskeleton of a beetle and chemical energy to the marathon runner. When attached to other molecules, like proteins or fats, they aid in communication between cells. But before we get any further into their uses, let’s talk structure.
The sugars we encounter most in basic biology have their five or six carbons linked together in a ring. There’s no need to dive deep into organic chemistry, but there are a couple of essential things to know to interpret the standard representations of these molecules.
Check out the sugars depicted in the figure. The top-left molecule, glucose, has six carbons, which have been numbered. The sugar to its right is the same glucose, with all but one “C” removed. The other five carbons are still there but are inferred using the conventions of organic chemistry: Anywhere there is a corner, there’s a carbon unless otherwise indicated. It might be a good exercise for you to add in a “C” over each corner so that you gain a good understanding of this convention. You should end up adding in five carbon symbols; the sixth is already given because that is conventionally included when it occurs outside of the ring.
On the left is a glucose with all of its carbons indicated. They’re also numbered, which is important to understand now for information that comes later. On the right is the same molecule, glucose, without the carbons indicated (except for the sixth one). Wherever there is a corner, there is a carbon, unless otherwise indicated (as with the oxygen). On the bottom left is ribose, the sugar found in RNA. The sugar on the bottom right is deoxyribose. Note that at carbon 2 (*), the ribose and deoxyribose differ by a single oxygen.
The lower left sugar in the figure is a ribose. In this depiction, the carbons, except the one outside of the ring, have not been drawn in, and they are not numbered. This is the standard way sugars are presented in texts. Can you tell how many carbons there are in this sugar? Count the corners and don’t forget the one that’s already indicated!
If you said “five,” you are right. Ribose is a pentose (pent = five) and happens to be the sugar present in ribonucleic acid, or RNA. Think to yourself what the sugar might be in deoxyribonucleic acid, or DNA. If you thought, deoxyribose, you’d be right.
The fourth sugar given in the figure is a deoxyribose. In organic chemistry, it’s not enough to know that corners indicate carbons. Each carbon also has a specific number, which becomes important in discussions of nucleic acids. Luckily, we get to keep our carbon counting pretty simple in basic biology. To count carbons, you start with the carbon to the right of the non-carbon corner of the molecule. The deoxyribose or ribose always looks to me like a little cupcake with a cherry on top. The “cherry” is an oxygen. To the right of that oxygen, we start counting carbons, so that corner to the right of the “cherry” is the first carbon. Now, keep counting. Here’s a little test: What is hanging down from carbon 2 of the deoxyribose?
If you said a hydrogen (H), you are right! Now, compare the deoxyribose to the ribose. Do you see the difference in what hangs off of the carbon 2 of each sugar? You’ll see that the carbon 2 of ribose has an –OH, rather than an H. The reason the deoxyribose is called that is because the O on the second carbon of the ribose has been removed, leaving a “deoxyed” ribose. This tiny distinction between the sugars used in DNA and RNA is significant enough in biology that we use it to distinguish the two nucleic acids.
In fact, these subtle differences in sugars mean big differences for many biological molecules. Below, you’ll find a couple of ways that apparently small changes in a sugar molecule can mean big changes in what it does. These little changes make the difference between a delicious sugar cookie and the crunchy exoskeleton of a dung beetle.
Sugar and Fuel
A marathon runner keeps fuel on hand in the form of “carbs,” or sugars. These fuels provide the marathoner’s straining body with the energy it needs to keep the muscles pumping. When we take in sugar like this, it often comes in the form of glucose molecules attached together in a polymer called starch. We are especially equipped to start breaking off individual glucose molecules the minute we start chewing on a starch.
Double X Extra: A monomer is a building block (mono = one) and a polymer is a chain of monomers. With a few dozen monomers or building blocks, we get millions of different polymers. That may sound nutty until you think of the infinity of values that can be built using only the numbers 0 through 9 as building blocks or the intricate programming that is done using only a binary code of zeros and ones in different combinations.
Our bodies then can rapidly take the single molecules, or monomers, into cells and crack open the chemical bonds to transform the energy for use. The bonds of a sugar are packed with chemical energy that we capture to build a different kind of energy-containing molecule that our muscles access easily. Most species rely on this process of capturing energy from sugars and transforming it for specific purposes.
Polysaccharides: Fuel and Form
Plants use the Sun’s energy to make their own glucose, and starch is actually a plant’s way of storing up that sugar. Potatoes, for example, are quite good at packing away tons of glucose molecules and are known to dieticians as a “starchy” vegetable. The glucose molecules in starch are packed fairly closely together. A string of sugar molecules bonded together through dehydration synthesis, as they are in starch, is a polymer called a polysaccharide (poly = many; saccharide = sugar). When the monomers of the polysaccharide are released, as when our bodies break them up, the reaction that releases them is called hydrolysis.
Double X Extra: The specific reaction that hooks one monomer to another in a covalent bond is called dehydration synthesis because in making the bond–synthesizing the larger molecule–a molecule of water is removed (dehydration). The reverse is hydrolysis (hydro = water; lysis = breaking), which breaks the covalent bond by the addition of a molecule of water.
Although plants make their own glucose and animals acquire it by eating the plants, animals can also package away the glucose they eat for later use. Animals, including humans, store glucose in a polysaccharide called glycogen, which is more branched than starch. In us, we build this energy reserve primarily in the liver and access it when our glucose levels drop.
Whether starch or glycogen, the glucose molecules that are stored are bonded together so that all of the molecules are oriented the same way. If you view the sixth carbon of the glucose to be a “carbon flag,” you’ll see in the figure that all of the glucose molecules in starch are oriented with their carbon flags on the upper left.
The orientation of monomers of glucose in polysaccharides can make a big difference in the use of the polymer. The glucoses in the molecule on the top are all oriented “up” and form starch. The glucoses in the molecule on the bottom alternate orientation to form cellulose, which is quite different in its function from starch.
Storing up sugars for fuel and using them as fuel isn’t the end of the uses of sugar. In fact, sugars serve as structural molecules in a huge variety of organisms, including fungi, bacteria, plants, and insects.
The primary structural role of a sugar is as a component of the cell wall, giving the organism support against gravity. In plants, the familiar old glucose molecule serves as one building block of the plant cell wall, but with a catch: The molecules are oriented in an alternating up-down fashion. The resulting structural sugar is called cellulose.
That simple difference in orientation means the difference between a polysaccharide as fuel for us and a polysaccharide as structure. Insects take it step further with the polysaccharide that makes up their exoskeleton, or outer shell. Once again, the building block is glucose, arranged as it is in cellulose, in an alternating conformation. But in insects, each glucose has a little extra added on, a chemical group called an N-acetyl group. This addition of a single functional group alters the use of cellulose and turns it into a structural molecule that gives bugs that special crunchy sound when you accidentally…ahem…step on them.
These variations on the simple theme of a basic carbon-ring-as-building-block occur again and again in biological systems. In addition to serving roles in structure and as fuel, sugars also play a role in function. The attachment of subtly different sugar molecules to a protein or a lipid is one way cells communicate chemically with one another in refined, regulated interactions. It’s as though the cells talk with each other using a specialized, sugar-based vocabulary. Typically, cells display these sugary messages to the outside world, making them available to other cells that can recognize the molecular language.
Lipids: The Fatty Trifecta
Starch makes for good, accessible fuel, something that we immediately attack chemically and break up for quick energy. But fats are energy that we are supposed to bank away for a good long time and break out in times of deprivation. Like sugars, fats serve several purposes, including as a dense source of energy and as a universal structural component of cell membranes everywhere.
Fats: the Good, the Bad, the Neutral
Turn again to a nutrition label, and you’ll see a few references to fats, also known as lipids. (Fats are slightly less confusing that sugars in that they have only two names.) The label may break down fats into categories, including trans fats, saturated fats, unsaturated fats, and cholesterol. You may have learned that trans fats are “bad” and that there is good cholesterol and bad cholesterol, but what does it all mean?
Let’s start with what we mean when we say saturated fat. The question is, saturated with what? There is a specific kind of dietary fat call the triglyceride. As its name implies, it has a structural motif in which something is repeated three times. That something is a chain of carbons and hydrogens, hanging off in triplicate from a head made of glycerol, as the figure shows. Those three carbon-hydrogen chains, or fatty acids, are the “tri” in a triglyceride. Chains like this can be many carbons long.
Double X Extra: We call a fatty acid a fatty acid because it’s got a carboxylic acid attached to a fatty tail. A triglyceride consists of three of these fatty acids attached to a molecule called glycerol. Our dietary fat primarily consists of these triglycerides.
Triglycerides come in several forms. You may recall that carbon can form several different kinds of bonds, including single bonds, as with hydrogen, and double bonds, as with itself. A chain of carbon and hydrogens can have every single available carbon bond taken by a hydrogen in single covalent bond. This scenario of hydrogen saturation yields a saturated fat. The fat is saturated to its fullest with every covalent bond taken by hydrogens single bonded to the carbons.
Saturated fats have predictable characteristics. They lie flat easily and stick to each other, meaning that at room temperature, they form a dense solid. You will realize this if you find a little bit of fat on you to pinch. Does it feel pretty solid? That’s because animal fat is saturated fat. The fat on a steak is also solid at room temperature, and in fact, it takes a pretty high heat to loosen it up enough to become liquid. Animals are not the only organisms that produce saturated fat–avocados and coconuts also are known for their saturated fat content.
The top graphic above depicts a triglyceride with the glycerol, acid, and three hydrocarbon tails. The tails of this saturated fat, with every possible hydrogen space occupied, lie comparatively flat on one another, and this kind of fat is solid at room temperature. The fat on the bottom, however, is unsaturated, with bends or kinks wherever two carbons have double bonded, booting a couple of hydrogens and making this fat unsaturated, or lacking some hydrogens. Because of the space between the bumps, this fat is probably not solid at room temperature, but liquid.
You can probably now guess what an unsaturated fat is–one that has one or more hydrogens missing. Instead of single bonding with hydrogens at every available space, two or more carbons in an unsaturated fat chain will form a double bond with carbon, leaving no space for a hydrogen. Because some carbons in the chain share two pairs of electrons, they physically draw closer to one another than they do in a single bond. This tighter bonding result in a “kink” in the fatty acid chain.
In a fat with these kinks, the three fatty acids don’t lie as densely packed with each other as they do in a saturated fat. The kinks leave spaces between them. Thus, unsaturated fats are less dense than saturated fats and often will be liquid at room temperature. A good example of a liquid unsaturated fat at room temperature is canola oil.
A few decades ago, food scientists discovered that unsaturated fats could be resaturated or hydrogenated to behave more like saturated fats and have a longer shelf life. The process of hydrogenation–adding in hydrogens–yields trans fat. This kind of processed fat is now frowned upon and is being removed from many foods because of its associations with adverse health effects. If you check a food label and it lists among the ingredients “partially hydrogenated” oils, that can mean that the food contains trans fat.
Double X Extra: A triglyceride can have up to three different fatty acids attached to it. Canola oil, for example, consists primarily of oleic acid, linoleic acid, and linolenic acid, all of which are unsaturated fatty acids with 18 carbons in their chains.
Why do we take in fat anyway? Fat is a necessary nutrient for everything from our nervous systems to our circulatory health. It also, under appropriate conditions, is an excellent way to store up densely packaged energy for the times when stores are running low. We really can’t live very well without it.
Phospholipids: An Abundant Fat
You may have heard that oil and water don’t mix, and indeed, it is something you can observe for yourself. Drop a pat of butter–pure saturated fat–into a bowl of water and watch it just sit there. Even if you try mixing it with a spoon, it will just sit there. Now, drop a spoon of salt into the water and stir it a bit. The salt seems to vanish. You’ve just illustrated the difference between a water-fearing (hydrophobic) and a water-loving (hydrophilic) substance.
Generally speaking, compounds that have an unequal sharing of electrons (like ions or anything with a covalent bond between oxygen and hydrogen or nitrogen and hydrogen) will be hydrophilic. The reason is that a charge or an unequal electron sharing gives the molecule polarity that allows it to interact with water through hydrogen bonds. A fat, however, consists largely of hydrogen and carbon in those long chains. Carbon and hydrogen have roughly equivalent electronegativities, and their electron-sharing relationship is relatively nonpolar. Fat, lacking in polarity, doesn’t interact with water. As the butter demonstrated, it just sits there.
There is one exception to that little maxim about fat and water, and that exception is the phospholipid. This lipid has a special structure that makes it just right for the job it does: forming the membranes of cells. A phospholipid consists of a polar phosphate head–P and O don’t share equally–and a couple of nonpolar hydrocarbon tails, as the figure shows. If you look at the figure, you’ll see that one of the two tails has a little kick in it, thanks to a double bond between the two carbons there.
Phospholipids form a double layer and are the major structural components of cell membranes. Their bend, or kick, in one of the hydrocarbon tails helps ensure fluidity of the cell membrane. The molecules are bipolar, with hydrophilic heads for interacting with the internal and external watery environments of the cell and hydrophobic tails that help cell membranes behave as general security guards.
The kick and the bipolar (hydrophobic and hydrophilic) nature of the phospholipid make it the perfect molecule for building a cell membrane. A cell needs a watery outside to survive. It also needs a watery inside to survive. Thus, it must face the inside and outside worlds with something that interacts well with water. But it also must protect itself against unwanted intruders, providing a barrier that keeps unwanted things out and keeps necessary molecules in.
Phospholipids achieve it all. They assemble into a double layer around a cell but orient to allow interaction with the watery external and internal environments. On the layer facing the inside of the cell, the phospholipids orient their polar, hydrophilic heads to the watery inner environment and their tails away from it. On the layer to the outside of the cell, they do the same.
As the figure shows, the result is a double layer of phospholipids with each layer facing a polar, hydrophilic head to the watery environments. The tails of each layer face one another. They form a hydrophobic, fatty moat around a cell that serves as a general gatekeeper, much in the way that your skin does for you. Charged particles cannot simply slip across this fatty moat because they can’t interact with it. And to keep the fat fluid, one tail of each phospholipid has that little kick, giving the cell membrane a fluid, liquidy flow and keeping it from being solid and unforgiving at temperatures in which cells thrive.
Steroids: Here to Pump You Up?
Our final molecule in the lipid fatty trifecta is cholesterol. As you may have heard, there are a few different kinds of cholesterol, some of which we consider to be “good” and some of which is “bad.” The good cholesterol, high-density lipoprotein, or HDL, in part helps us out because it removes the bad cholesterol, low-density lipoprotein or LDL, from our blood. The presence of LDL is associated with inflammation of the lining of the blood vessels, which can lead to a variety of health problems.
But cholesterol has some other reasons for existing. One of its roles is in the maintenance of cell membrane fluidity. Cholesterol is inserted throughout the lipid bilayer and serves as a block to the fatty tails that might otherwise stick together and become a bit too solid.
Cholesterol’s other starring role as a lipid is as the starting molecule for a class of hormones we called steroids or steroid hormones. With a few snips here and additions there, cholesterol can be changed into the steroid hormones progesterone, testosterone, or estrogen. These molecules look quite similar, but they play very different roles in organisms. Testosterone, for example, generally masculinizes vertebrates (animals with backbones), while progesterone and estrogen play a role in regulating the ovulatory cycle.
Double X Extra: A hormone is a blood-borne signaling molecule. It can be lipid based, like testosterone, or short protein, like insulin.
As you progress through learning biology, one thing will become more and more clear: Most cells function primarily as protein factories. It may surprise you to learn that proteins, which we often talk about in terms of food intake, are the fundamental molecule of many of life’s processes. Enzymes, for example, form a single broad category of proteins, but there are millions of them, each one governing a small step in the molecular pathways that are required for living.
Levels of Structure
Amino acids are the building blocks of proteins. A few amino acids strung together is called a peptide, while many many peptides linked together form a polypeptide. When many amino acids strung together interact with each other to form a properly folded molecule, we call that molecule a protein.
For a string of amino acids to ultimately fold up into an active protein, they must first be assembled in the correct order. The code for their assembly lies in the DNA, but once that code has been read and the amino acid chain built, we call that simple, unfolded chain the primary structure of the protein.
This chain can consist of hundreds of amino acids that interact all along the sequence. Some amino acids are hydrophobic and some are hydrophilic. In this context, like interacts best with like, so the hydrophobic amino acids will interact with one another, and the hydrophilic amino acids will interact together. As these contacts occur along the string of molecules, different conformations will arise in different parts of the chain. We call these different conformations along the amino acid chain the protein’s secondary structure.
Once those interactions have occurred, the protein can fold into its final, or tertiary structure and be ready to serve as an active participant in cellular processes. To achieve the tertiary structure, the amino acid chain’s secondary interactions must usually be ongoing, and the pH, temperature, and salt balance must be just right to facilitate the folding. This tertiary folding takes place through interactions of the secondary structures along the different parts of the amino acid chain.
The final product is a properly folded protein. If we could see it with the naked eye, it might look a lot like a wadded up string of pearls, but that “wadded up” look is misleading. Protein folding is a carefully regulated process that is determined at its core by the amino acids in the chain: their hydrophobicity and hydrophilicity and how they interact together.
In many instances, however, a complete protein consists of more than one amino acid chain, and the complete protein has two or more interacting strings of amino acids. A good example is hemoglobin in red blood cells. Its job is to grab oxygen and deliver it to the body’s tissues. A complete hemoglobin protein consists of four separate amino acid chains all properly folded into their tertiary structures and interacting as a single unit. In cases like this involving two or more interacting amino acid chains, we say that the final protein has a quaternary structure. Some proteins can consist of as many as a dozen interacting chains, behaving as a single protein unit.
A Plethora of Purposes
What does a protein do? Let us count the ways. Really, that’s almost impossible because proteins do just about everything. Some of them tag things. Some of them destroy things. Some of them protect. Some mark cells as “self.” Some serve as structural materials, while others are highways or motors. They aid in communication, they operate as signaling molecules, they transfer molecules and cut them up, they interact with each other in complex, interrelated pathways to build things up and break things down. They regulate genes and package DNA, and they regulate and package each other.
As described above, proteins are the final folded arrangement of a string of amino acids. One way we obtain these building blocks for the millions of proteins our bodies make is through our diet. You may hear about foods that are high in protein or people eating high-protein diets to build muscle. When we take in those proteins, we can break them apart and use the amino acids that make them up to build proteins of our own.
How does a cell know which proteins to make? It has a code for building them, one that is especially guarded in a cellular vault in our cells called the nucleus. This code is deoxyribonucleic acid, or DNA. The cell makes a copy of this code and send it out to specialized structures that read it and build proteins based on what they read. As with any code, a typo–a mutation–can result in a message that doesn’t make as much sense. When the code gets changed, sometimes, the protein that the cell builds using that code will be changed, too.
Biohazard!The names associated with nucleic acids can be confusing because they all start with nucle-. It may seem obvious or easy now, but a brain freeze on a test could mix you up. You need to fix in your mind that the shorter term (10 letters, four syllables), nucleotide, refers to the smaller molecule, the three-part building block. The longer term (12 characters, including the space, and five syllables), nucleic acid, which is inherent in the names DNA and RNA, designates the big, long molecule.
DNA vs. RNA: A Matter of Structure
DNA and its nucleic acid cousin, ribonucleic acid, or RNA, are both made of the same kinds of building blocks. These building blocks are called nucleotides. Each nucleotide consists of three parts: a sugar (ribose for RNA and deoxyribose for DNA), a phosphate, and a nitrogenous base. In DNA, every nucleotide has identical sugars and phosphates, and in RNA, the sugar and phosphate are also the same for every nucleotide.
So what’s different? The nitrogenous bases. DNA has a set of four to use as its coding alphabet. These are the purines, adenine and guanine, and the pyrimidines, thymine and cytosine. The nucleotides are abbreviated by their initial letters as A, G, T, and C. From variations in the arrangement and number of these four molecules, all of the diversity of life arises. Just four different types of the nucleotide building blocks, and we have you, bacteria, wombats, and blue whales.
RNA is also basic at its core, consisting of only four different nucleotides. In fact, it uses three of the same nitrogenous bases as DNA–A, G, and C–but it substitutes a base called uracil (U) where DNA uses thymine. Uracil is a pyrimidine.
DNA vs. RNA: Function Wars
An interesting thing about the nitrogenous bases of the nucleotides is that they pair with each other, using hydrogen bonds, in a predictable way. An adenine will almost always bond with a thymine in DNA or a uracil in RNA, and cytosine and guanine will almost always bond with each other. This pairing capacity allows the cell to use a sequence of DNA and build either a new DNA sequence, using the old one as a template, or build an RNA sequence to make a copy of the DNA.
These two different uses of A-T/U and C-G base pairing serve two different purposes. DNA is copied into DNA usually when a cell is preparing to divide and needs two complete sets of DNA for the new cells. DNA is copied into RNA when the cell needs to send the code out of the vault so proteins can be built. The DNA stays safely where it belongs.
RNA is really a nucleic acid jack-of-all-trades. It not only serves as the copy of the DNA but also is the main component of the two types of cellular workers that read that copy and build proteins from it. At one point in this process, the three types of RNA come together in protein assembly to make sure the job is done right.
An historic view interpretation of the placenta (source).
She gave me a few minutes to meet my daughter before she reeled me back into a state that was my new reality. “You’re not finished Jeanne. You still need to birth your placenta.” What?!?! More pushing? But I was lucky and the efforts required to bring my placenta ex vivo were minimal.
This is the second placenta my body helped make. OK, so it doesn’t EXACTLY look like meatloaf…
The idea of a placenta, which is the only human organ to completely and temporarily develop after birth, was fascinating. That thing sitting in a rectangular periwinkle bucket was what allowed me to grow another human.. inside of my body! There was no way I was not going to check it out, as well as create a permanent record of its relatively short-lived existence.
My first impression was that it looked like “meatloaf.” Not necessarily a well made meatloaf, but perhaps one that is made by my mother (sorry mom). But, alas, chaos reigned and I wasn’t able to really take a good look. However, for my second birth and hence second placenta, my midwife indulged me with a more detailed look and a mini-lesson.
Baby’s eye view: Where geekling deux spent 39 weeks and 4 days.
Her gloved hands, still wet with my blood and amniotic fluid, slid into the opening that was artificially created with a tool resembling a crocheting needle. She opened the amniotic sac wide so I could get a baby’s eye view of the crimson organ that served as a nutritional trading post between me and my new bundle of joy.
She explained that the word “placenta” comes from from the Greek word plakoeis, which translates to “flat cake” (however, I’m sure if my mom’s meatloaf was more common in ancient Greece, the placenta would be named differently). “It’s one of the defining features of being a mammal,” she explained as I was working on another mammalian trait – getting my baby to nurse for the first time.
That was about all I could mentally digest at the time, but still, more than three years later, the placenta continues to fascinate me, mostly due to the fact that it is responsible for growing new life. It’s a natural topic for this long overdue Pregnancy101post, so let’s dive in!
Development of the placenta
It all starts when a fertilized egg implants itself into the wall of the uterus. But, in order to fully understand how it works, we should start with an overview of the newly formed embryo.
The very early stages of us (and many other things that are alive).
The trophoblast invades the uterus, leading to implantation of the blastocyst.
As soon as a male sperm cell fuses with a female egg cell, fertilization occurs and the cells begin to multiply. But, they remain contained within a tiny sphere. As the cells continue to divide, they are given precise instructions depending on their location within that sphere, and begin to transform into specific cell types. This process, which is called cellular differentiation, actually seals the fate every cell in our body, sort of like how we all have different jobs – some of us are transport things, some of us are involved in policing the neighborhoods, some of us build structures, some of us communicate information, some of us deal with food, some of us get rid of waste, etc. Every cell gets a job (it’s the only example of 100% employment rates!).
Now back to the cells in the fertilized egg. As they start to learn what their specific job will be, the cells within the sphere will start to organize themselves. After about 5 days after fertilization, the sphere of cells becomes something called a blastocyst, which readies itself for implantationinto the wall of the uterus.
The act of implantation is largely due to the cells found on the perimeter of the blastocyst sphere. These cells, collectively known as the trophoblast, release a very important hormone – human chorionic gonadotropin (hCG) – that tells the uterus to prepare for it’s new tenant. (If you recall, hCG is the hormone picked up by pregnancy tests.) Around day 7, the trophoblast cells start to invade the lining of the uterus, and begin to form the placenta. It is at this point that pregnancy officially begins. (Here is a cool video, created by the UNSW Embryology Department, showing the process of implantation.)
Structure of the placenta
Eventually the trophoblast becomes the recognizable organ that is the placenta. Consider the “flat cake” analogy, with the top of the cake being the fetal side (the side that is in contact with the baby), and the bottom of the cake being the maternal side (the side that is in contact with the mother).
Cross section of the placenta: Blood vessels originating from the fetus sit in a pool of maternal blood, which is constantly replenished my maternal arteries and veins. The red represents oxygenated blood, and the blue represents de-oxygenated blood.
Projecting from the center of the fetal side of the placenta are two arteries and one vein, coiled together in a long, rubbery rope, often bluish-grey in color. This umbilical cord serves as the tunnel through which nutrients and waste are shuttled, and essentially serves to plug the baby into the mother’s metabolic processes. At the umbilical cord-placenta nexus, the umbilical cord arteries and vein branch out into a network of blood vessels, which further divide into a tree-like mass of vessels within the placenta.
These tree-like masses originating from the umbilical cord (and thus fetus) sit in a cavity called the intervillous space, and are bathed in nutrient-rich maternal blood. This maternal blood, which provides the fetus with a means for both nutrient delivery and waste elimination, is continually replenished via a network of maternal arteries and veins that feed into the intervillous space. Furthermore, these arteries and veins help to anchor the placenta into the uterine wall. One of the most interesting aspects about the mother-feus relationship is that the blood vessel connection is indirect. This helps to prevent a detrimental immune response, which could lead to immunological rejection of the fetus (sort of like how a transplanted organ can become rejected by the recipient).
Functions of the placenta
Just like a plant needs sunlight, oxygen, and water to grow, a baby needs all sorts of nutrients to develop. And since a baby also produces waste, by nature of it being alive and all, there is an absolute requirement for waste removal. However, because we can’t just give a developing fetus food or a bottle, nor are we able to change diapers in utero, the onus lies completely on the biological mother.
This is where the placenta comes in. Because the fetus is plugged into the circulatory system of the mother via the umbilical cord and placenta, the fetus is provided with necessary nutrients and a mechanism to get rid of all the byproducts of metabolism. Essentially, the placenta acts as a waitress of sorts – providing the food, and cleaning it all up when the fetus is done eating.
But it’s not just about nutrition and waste. The placenta also serves as a hormone factory, making and secreting biological chemicals to help sustain the pregnancy. I mentioned above that the placenta produces hCG, which pretty much serves as a master regulator for pregnancy in that it helps control the production of maternally produced hormones, estrogen and progesterone. It also helps to suppress the mother’s immunological response to the placenta (along with other factors), which cloaks the growing baby, thereby hiding it from being viewed as a “foreign” invader (like a virus or bacteria).
Another hormone produced by the placenta is human placental lactogen (hPL), which tells the mother to increase her mammary tissue. This helps mom prepare for nursing her baby once it’s born, and is the primary reason why our boobs tend to get bigger when we are pregnant. (Yay for big boobies, but my question is, what the hell transforms our rear ends into giant double cheeseburgers, and what biological purpose does that serve?? But I digress…)
Despite the fact that the mother’s circulatory system remains separate from the baby’s circulatory system, there are a clear mixing of metabolic products (nutrients, waste, hormones, etc). In essence, if it is in mom’s blood stream, it will very likely pass into baby’s blood stream. This is the very reason that pregnant mothers are strongly advised to stay away from cigarettes, drugs, alcohol, and other toxic chemicals, all of which can easily pass through the placental barrier lying between mother and fetus. When moms do not heed this warning, the consequences can be devastating to the developing fetus, potentially leading to birth defects or even miscarriage.
There are also situations that could compromise the functions of the placenta – restriction of blood supply, loss of placental tissue, muted placental growth, just to name a few – reducing the chances of getting and/or staying pregnant. This placental insufficiency is generally accompanied by slow growth of the uterus, low rate of weight gain, and most importantly, reduced fetal growth.
And it’s not just the growth of the placenta that is important – where the placenta attaches to the uterus is also very important. When the placenta grows on top of the opening of the birth canal, the chances for a normal, vaginal birth are obliterated. This condition, known as placenta previa, is actually quite dangerous and can cuase severe bleeding in the third trimester. 0.5% of all women experience this, and it is one of the true medical conditions that absolutely requires a C-section.
Then, there is the issue of attachment. If the placenta doesn’t attach well to the uterus, it could end up peeling away from the uterine wall, which can cause vaginal bleeding, as well as deprive the baby from nutrient delivery and waste disposal. This abruption of the placenta is complicated by the use of drugs, smoking, blood clotting disorders, high blood pressure, or if the mother has diabetes or a history of placental abruption.
Conversely, there are times when the blood vessels originating from the placenta implant too deeply into the uterus, which can lead to a placenta accreta. If this occurs, the mother generally delivers via C-section, followed by a complete hysterectomy.
Cultural norms and the placenta
There are many instances where the placenta plays a huge role in the culture of a society. For instance, both the Maori people of New Zealand and the Navajopeople of Southwestern US will bury the placenta. There is also some folklore associated with the placenta, and several societies believe that it is alive, pehaps serving as a friend for the baby. But the tradition that seems to be making it’s way into the granola culture of the US is one that can be traced back to traditional Chinese practices: eating the placenta.
Placentophagy, or eating one’s own placenta, is very common among a variety of mammalian species. Biologically speaking, it is thought that animals that eat their own placenta do so to hide fresh births from predators, thereby increasing the chances of their babies’ survival. Others have suggested that eating the nutrient-rich placenta helps mothers to recover after giving birth.
However, these days, a growing number of new mothers are opting to ingest that which left their own body (likely) through their own vaginas. And they are doing so though a very expensive process involving dehydrating and encapsulating placental tissue.
Why would one go through this process? The claims are that placentophagy will help ward of post partum depression, increase the supply of milk in a lactating mother, and even slow down the ageing process. But, alas, these are some pretty bold claims that are substantiated only by anecdata, and not actual science (see this).
So, even though my placentas looked like meatloaf, there was no way I was eating them. If you are considering this, I’d approach the issue with great skepticism. There are many a people who will take advantage of maternal vulnerabilities in the name of cold hard cash. And, always remember, if the claims sound to good to be true, they probably are!
Thanks for tuning into this issue of Pregnancy101, and enjoy this hat, and a video!
[Editor's note: We are pleased to be able to run this post by Dr. Kate Clancy that first appeared at Clancy's Scientific American blog, the wonderful Context and Variation. Clancy is an Assistant Professor of Anthropology at the University of Illinois. She studies the evolutionary medicine of women’s reproductive physiology, and blogs about her field, the evolution of human behavior and issues for women in science. You can follow her on Twitter--which we strongly recommend, particularly if you're interested in human behavior, evolutionary medicine, and ladybusiness--@KateClancy.]
Over the course of my training to become a biological anthropologist with a specialty in women’s reproductive ecology and life history theory, or ladybusiness expert, I have learned a lot about miscarriage. Only it wasn’t miscarriage, it was spontaneous abortion. Except that some didn’t like the term spontaneous abortion and used intrauterine mortality (Wood, 1994). Or fetal loss. Fetal loss is probably the most common.
There is also pregnancy loss (Holman and Wood, 2001). You can use that term, too. Oh, or aContinue reading →
Jeanne, would you like some…peeeaaasss? License information here.
I was seven weeks deep when it hit me. Suddenly, I was in a chronic state of queasiness. Under most circumstances, I had it under control. Sure, I would gag every time I brushed my teeth, but (mostly) I could keep it all down. Then I went to my aunt Diane’s house for dinner.
Aunt Diane rolls with a crowd of self-made Italian chefs and, as a result, most of her cooking falls under the “rustic Italian” umbrella. It is not uncommon to see sitting in her cupboard a massive inventory of jarred plum tomatoes or for an entire section of her freezer to be dedicated to homemade vodka sauce, always frozen in those takeaway containers that originally brought us egg drop soup. Under normal circumstances, I’d be psyched to eat over.
I don’t recall the entire menu, but there is one side dish that has been forever burned into memory, and not in a good way. I remember starring at my plate, specifically at the heaping pile of sautéed peas. I kept rearranging the peas on my plate, sometimes spreading them out, sometimes piling them up. Then Diane looked at me and excitedly asked, “Jeanne, did you try my peas? I made them just for you!” I don’t know what compelled her to make these peas for me. Perhaps it was because I am a vegetarian and the rest of the meal involved meat? But, there they were, staring me down, and there Diane was, watching with anticipation, waiting for my approval.
Because I adore my aunt Diane and I wanted to make her happy (after all, she did just cook an entire meal for my small family), I scooped up a moderate amount of peas with my fork and deposited them in my mouth. I had to use every fiber of my being to chew them, and even more effort to actually swallow. My body was not cooperating and I had to implement a state of near meditation to keep them from coming back up. Luckily, I kept my cool and was able coerce my face into showing a smile while simultaneously telling my aunt and friend that her peas were delicious.
Credit: Jeanne Garbarino.
My husband picked up on my soaring level of discomfort and without missing a beat, ate all my peas when Diane wasn’t looking. We ended the evening with my stomach contents intact, but barely.
The next morning, as I was preparing my 18 month-old daughter’s daycare lunch, I remembered that we were provided with a parting gift of sautéed peas. I took them out of the fridge and proceeded to aliquot them into containers more suitable for a toddler. As I removed the lid, the onion-tinged aroma of Diane’s sautéed spring peas smacked me across my face. My body was clearly angry about what I had done to it the night before and, as if it were in a state of protest, I found myself sprinting to the bathroom where I began to puke.
From that day forth, I could not eat peas, let alone see or smell them, without eliciting extreme nausea. It didn’t matter what time of day, the mere presence of peas, although not necessary, was sufficient to make me toss my, well, peas.
It has long been known that nausea and vomiting are common symptoms of pregnancy. In fact, documentation of this phenomenon goes as far back as 2000 BC. However, the term “morning sickness” is a complete misnomer. For one, pregnancy-related nausea and vomiting is not just a morning thing. It can happen at any time of day. Second, the term “sickness” suggests a state of unhealthiness. We know that perfectly healthy pregnant women who deliver perfectly healthy babies experience morning sickness, and this type of nausea and vomiting is not an indicator of maternal and/or fetal health.
But, that doesn’t change the fact that it sucks.
Morning sickness, more appropriately known as nausea and vomiting in pregnancy (NVP), affects approximately two-thirds of women in their first trimester of pregnancy. In many cases, morning sickness subsides at the end of the first trimester. In other cases, the symptoms of morning sickness can last for the entire pregnancy. For both my pregnancies, I experienced morning sickness for the first 5 months.
I feel so lucky.
No one really knows the exact mechanisms responsible for the onset morning sickness. We do know that the drastic hormonal changes that occur during early pregnancy certainly play a role; however, these effects are likely indirect. For instance, estrogen levels do not differ between pregnant women with morning sickness and those who do not experience symptoms. Furthermore, there is no causal relationship between human chorionic gonadotropin (hCG), the early pregnancy hormone detected by pregnancy tests, and morning sickness, despite the fact that peak hCG levels and peak severity of pregnancy-related nausea and vomiting occur at approximately the same time.
Based on these observations, scientists suggest that the hormonal fluctuations in pregnant women can elicit different responses in an individual, rendering some extremely susceptible and others remarkably resistant to the same stimulus (with regard to nausea and vomiting). This begs the question: Is there a genetic predisposition to morning sickness?
While a “morning sickness” gene has not been identified, a few lines of evidence point toward a potential for inheriting the tendency. For instance, identical twins, are fairly likely to share a tendency to morning sickness. Also, you are more likely to experience morning sickness if your mom experienced it, too. Even though genetics may be involved, the onset of morning sickness is probably what scientists call “multifactorial,” a result of a very complex interaction between genetics and environment, making it difficult to find a treatment that is effective and safe for everyone.
Until more is known, we are stuck eating saltines and sour candy. At least it’s something, right?
Food aversions and morning sickness
Make them if you dare. Credit: Jeanne Garbarino.
For my first pregnancy, it was smoked salmon, which I probably shouldn’t have been eating in the first place. For my second pregnancy, it was peas. (Interestingly, my aunt Diane initially provided both foods, which, after that initial consumption, was immediately followed by the onset of morning sickness.) The mere sight of either peas or smoked salmon elicited an uncomfortable queasiness that often culminated with a sprint to the porcelain throne. Apparently, this type of experience is pretty normal.
Developing an aversion to a specific tastes and smells during pregnancy is an extremely common phenomenon. In fact, between 50–90% of pregnant women worldwide experience some level of food aversion, with the most common aversions being meat, fish, poultry, and eggs. Furthermore, research suggests that food aversions developed during pregnancy are actually novel as opposed to an exaggeration of a pre-existing dislike for a certain food.
Complementing the development of food aversions is the report that dietary changes in pregnant woman are often related to changes in olfaction, or sense of smell. More specifically, some pregnant women experience increased sensitivity to certain odors, and usually in an unpleasant way. This heightened sensitivity is thought to be protective against foods that could pose a problem for mother and baby, such as those that have become rancid.
When I was pregnant, the self-perceived powerfully pungent scent of peas could have probably knocked me over if it was translated into some other physical force. I wish I had a gas mask.
Is there some benefit to morning sickness?
In general, nausea and vomiting are a defense mechanism, acting to protect us from the accidental ingestion of toxins. While morning sickness is likely a very complicated condition that needs further study, a popular explanation suggests that morning sickness is beneficial to both mother and fetus.
Several lines of observations support this idea, formally called the “maternal and embryo protection hypothesis”: (a) peak sensitivity to morning sickness occurs at approximately the same time that embryo development is most susceptible to toxins and chemical agents; and (b) women who experience morning sickness during their pregnancy are less likely to miscarry compared to women who do not experience morning sickness.
In essence, the maternal and embryo protection hypothesis suggests that morning sickness is an adaptive process, contributing to evolutionary success (measured in terms of how many of your genes are present in later generations). However, morning sickness is not found in all societies. One possible explanation for this is that those societies that do not widely experience morning sickness are significantly more likely to have plant-based diets (meats spoil much faster than plants). Another argument against evolutionary adaptation is that morning sickness has been documented only in three other species: domestic dogs, captive rhesus macaques, and captive chimpanzees.
It makes sense that the pregnancy-related nausea and vomiting widely known as morning sickness is a means to help protect mom and baby. It makes sense that women have a mechanism to detect and/or expel toxins and potentially harmful microorganisms if ingested. But the idea that morning sickness is actually a product of evolution is still under debate.
And even as a biologist, if I ever have to go through morning sickness again, the idea that it could be protective won’t really bring me comfort as I am puking up my guts. But, biology is biology and sometimes we just have to deal with it.
Andrews, P. and Whitehead, S. Pregnancy Sickness. American Physiological Society. 1990 February;5: 5-10.
Flaxman, S.M. and Sherman, P.W. Morning Sickness: A mechanism for protecting mother and baby. The Quarterly Review of Biology. 2000 June; 75(2):
Goodwin, TM. Nausea and vomiting of pregnancy: an obstetric syndrome. American Journal Obstetrics and Gynecology. 2002; 185(5): 184-189.
Kich, K.L. Gastrointestinal factors in nausea and vomiting of pregnancy. American Journal Obstetrics and Gynecology. 2002; 185(5): 198-203.
Nordin, S., Broman, D.A., Olofsson, J.K., Wulff, M. A Longitudinal Descriptive Study of Self-reported Abnormal Smell and Taste Perception in Pregnant Women. Chemical Senses. 2004; 29 (5): 391-402
NYC Campaign to alert the authorities if you see something suspicious. Antibodies are like the citizens that tell our body that something fishy is going down.
By Biology Editor, Jeanne Garbarino
There is a campaign sponsored by NYC’s Metropolitan Transit Authority (MTA) encouraging citizens to speak up if they see any activity or persons acting in a suspicious manner. Plastered all over buses, subways, and commuter rails are posters with the following message: If you see something, say something. This type of imagery reminds me very much of our own biological warning system programmed to, in essence, “speak up” should a suspicious character of the microscopic kind make it’s way into our bodies. It is through our immune response that our bodies “say something” in the event of infection.
At the very crux of the immune response are tiny proteins called antibodies, which are basically like the citizens that report any suspicious activities. Antibodies often travel in the blood stream, and upon crossing paths with a foreign invader (bacteria, virus, etc.), an antibody will flag it down and alert the “local authorities” of the body (aka immune cells).
For many years, scientists have been studying antibodies and their role in the immune response, revealing many aspects surrounding their structure and function. And through these studies, we have figured out how to use antibodies in ways that go beyond the immune system. For instance, antibodies against human chorionic growth hormone, or hCG, are the essential ingredients in home pregnancy tests. More recently, scientists have, in many ways, harnessed the power of antibodies for pharmaceutical uses. A very popular example of this is the drug Remicade, which is used to treat severe autoimmune diseases like rheumatoid arthritis and Crohn’s Disease. But, what exactly are antibodies and how do they work?
Well, I am glad I asked me that question.
As I mentioned, antibodies are proteins that we make. Specifically, they are produced by specialized immune cells called B-cells, which are the main players during our humoral immune response. B-cells will either secrete an antibody, which can then float around the circulatory system, or the antibody can remain attached to the outside of the B-cell. If there is something “foreign” in our bodies, such as a virus or bacterium, antibodies will recognize and attach itself to the invader, which is scientifically referred to as an antigen. When an antibody attaches to an antigen, it signals to our body to get rid of it. Amazingly, each antibody can only recognize 1 antigen, which is why we need so many different types of antibodies!
To get a better idea of how antibodies work, it is important to learn their basic structure. Antibodies are ‘Y’ shaped proteins, and have both constant and variable regions. The constant region is the same among all antibodies within a specific class (there are several different classes), where as the variable region is the portion of the antibody that is designed to recognize a specific antigen.
To better explain this, consider the antibody to be a lacrosse stick. The “stick” part is the constant region, and the mesh part is the variable region. Now consider the lacrosse ball to be the antigen (i.e. bacterium or virus). Only the lacrosse ball that is a triangle can fit into the lacrosse stick with the triangle-shaped mesh pocket. The same is true for the circle. And so on. Once the ball fits into the mesh, meaning, once the antibody binds the antigen, a cascade of events is set off, essentially sounding the alarm. Under normal, healthy circumstances, we take care of the antigen and the infectious agent is removed. (Note: there are different classes of antibodies and each class has it’s own “stick” part.)
A basic analology for how antibodies work.
Building off our understanding of how antibodies work, scientists have been able to develop monoclonal antibody therapy, which is the use of specific antibodies to stimulate an immune response against a disease. For instance, we now use monoclonal antibody therapy to combat a variety of cancers by injecting cancer patients with antibodies designed to recognize specific components on the surface of tumor cells. This helps signal to the body that it should turn on the immune response and get rid of the tumor cells.
The list of conditions where monoclonal antibody is a potential therapy is growing, and includes a variety of autoimmune diseases and cancers, post-organ transplant therapy, human respiratory syncytial virus (RSV) infections in children, and most recently hemophilia A. Also being explored is the use of monoclonal antibody therapy for addiction, which could essentially revolutionize how we can help people kick extremely difficult habits (i.e. cocaine or methamphetamine).
Despite the thousands of tedious and repetitive assays I’ve done using antibodies in my own laboratory, I know that I can never lose sight of how amazing these little proteins are.
———————————————- This post is a mental appetizer for another post on monoclonal antibodies by DXS tech editor, Jeffrey Perkel. His post specifically discusses the potential use of monoclonal antibodyto treat the X-linked blood disorder, hemophilia A. Read about it here.