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.
Looking to let go of a little “mommy guilt” for using the television now and then to give yourself a breather? There may be plenty of evidence that leaving children to watch too much television is a bad idea, but there is something to the idea that educational TV is, well, educational. We have the brain scans to prove it!
A study published in PLOS Biology used functional MRI scans to check out the brains of 26 children and 20 adults while they watched 20 minutes of Sesame Street. The actual purpose of the study wasn’t to find out if Sesame Street was educational per se. Rather, it was to observe the neural processes in the brain while a child is learning “naturalistically” and then see whether what they saw could predict how well the children would perform on standardized IQ tests.
Often, participants in studies receive fMRI scans while they are doing some sort of task that is supposed to simulate learning and/or stimulate certain neural processes. For example, a study subject might be asked to put together a three-dimensional puzzle on a computer (so their head remains still enough for the scan) to see how the brain interprets spatial relations.
However, these sorts of oversimplified “lab” tasks are not always representative of real-world activities, so it’s not clear whether what the researchers see on the brain images during these tasks is necessarily indicative of what REAL-life spatial relations thinking looks like. Are the neural processes seen in an fMRI scan while putting together blocks on a computer screen the same as what’s seen in the brain while a person builds a treehouse?
In this study, the researchers found a partial answer to exactly that kind of question, and the answer is no.
The children in study, ranging in age from 4 to 11 and all typically developing, watched the same 20-minute montage of short clips with Big Bird, Cookie Monster, the Count, Oscar and the rest of the gang teaching numbers and letters, shapes and colors, planets and countries, and so on. Meanwhile, the fMRI was taking a snapshot of their brain every two seconds.
The fMRI (which uses a giant magnet, not radiation, to peek into the brain) works by dividing the brain into a 3-D grid so that it can measure the intensity of the brain signals in each little section (about 40,000 of them, called voxels). The researchers collected a total of 609 images of each participant’s brain, which they could then use to map out the neural processes of the participants while they were watching.
They also had the children (23 of them), in a separate fMRI scanning period, perform a one of those lab-only fMRI tasks. In this case, the kids matched isolated pairs of faces, numbers, words and shapes on the computer (they pressed a button if the two images shown matched) while the fMRI images of their brains were created.
Finally, the children (19 of them) took IQ tests that primarily tested their math and verbal skills. Then the researchers analyzed the maps of neural processes in the children and their comparisons with the adults.
They found a couple of interesting things. First, the kids whose neural “maps” were most similar to the adults also performed the best on the IQ tests. This means kids’ brain structure matures in a predictable way, which the researchers called “neural maturity.”
“Broadly speaking, the children showed group-level similarity to adults in cortical regions associated with vision (occipital cortex), auditory processing (lateral temporal cortex), language (frontal and temporal cortex), visuo-spatial processing and calculation (intraparietal cortex), and several other functions,” the authors wrote.
The fMRI scan on the left represents correlations in neural activity between children and adults, in the middle between children and other children, and on the right between adults and other adults. Such neural maps, says University of Rochester cognitive scientist Jessica Cantlon, reveal how the brain’s neural structure develops along predictable pathways as we mature.
Second, the brain maps created during the Sesame Street viewing accurately predicted how the children performed on the IQ tests. Kids who did better on the verbal tasks showed more mature neural patterns in a part of the brain that handles speech and language, called the Broca area. Meanwhile, the kids whose math scores were highest had more neural maturity in a part of the brain that processes numbers, called intraparietal sulcus.
But the researchers’ other finding was that those areas of neural maturity seen during Sesame Street viewing — the ones that matched up with the children’s scores on the IQ test — were not seen during the fMRI task of matching faces, numbers, words and shapes. Basically, the “let’s try to simulate what learning looks like in the brain” task designed specifically for fMRI scans didn’t help much. But the more naturalistic, organic learning that takes places while watching Sesame Street did work.
Researchers now know they can use activities like viewing educational TV to scan children’s brains and learn more about how they learn — and it’s more accurate and helpful than invented computer tasks. It’s possible this technology and research could be applied to understanding better what’s going on with certain learning disabilities.
But a nice additional finding is that, hey, Sesame Street really IS educational! Of course, my son’s favorite show is a different PBS production — Dinosaur Train (which I admit I enjoy too) — so I also feel a better that little D spends a half hour or two, several days a week, learning from Buddy the Tyrannosaurus Rex, Tiny the Pteranodon, Mr. Conductor and Dr. Scott the Paleontologist about dinosaurs, carnivores, herbivores and how to test a hypothesis. All aboard!
A scanning electron micrograph of a blood clot. Image credit: Steve Gschmeissner/Science Photo Library (http://www.sciencephoto.com/media/203271/enlarge#)
On Monday January 1st, I overheard my dad telling my mom how his left arm was numb and that he had no strength in his left hand. I immediately ran into the medicine cabinet, grabbed two aspirin, practically shoved them down my dad’s throat, and told him to get his coat. He was going to the ER.
As it turns out, my dad was having a stroke, which is basically the cessation of blood flow to an area in the brain. Luckily, my dad only suffered a very mild stroke, and after several days of monitoring and a battery of tests, he was released from the hospital.
While we are all relieved that he dodged what could have been a fatal bullet, I came to realize that there was only a superficial understanding of what was actually happening. So, to help demystify the process for my dad (and anyone else in this situation), I’ve decided to write a mini-guide on strokes. Below you will find some handy information about strokes, including what they are, as well as a glossary of relevant terms.
Why we need blood flow in the brain
Before I get into what happens to the brain when a stroke occurs, it is important to first understand why unrestricted blood flow in blood vessels in the brain is important. The brain is a type of tissue, and like all tissues in our body, it needs a constant access to nutrients and oxygen. Furthermore, tissues produce waste, and this waste needs to be removed.
The human cardiovascular system. Image Credit: Wikipedia.
Evolution’s solution to this problem is the development of a vast network of blood vessels existing within our tissues. For instance, take a good look at your very own eyeballs. Especially when we are tired, we can see tiny blood vessels called capillaries, which help to deliver key nutrients and oxygen, keeping our organs of sight healthy and happy. Now consider that this type of blood vessel network exists in all tissues in our bodies (because it does). Depending on the needs of the tissue, these vessels vary in size and number. Sometimes the blood vessels are large, like the aorta, and sometimes they are super tiny, like the capillaries in our eyes. However, all serve the same function: to make sure that cells can breath, eat, and get rid of waste.
When blood is prevented from traveling to a specific area within a tissue, the cells in that area will not get enough fuel and oxygen and will begin to die. For instance, the restriction of blood flow to the heart leads to the death of heart tissue, causing a heart attack. Similarly, the interruption of normal blood flow within the brain causes the affected cells in the brain to essentially starve, suffocate, and die, resulting in a stroke. The medical term for a lack of oxygen delivery to tissues due to a restriction in blood flow is ischemia. In general, the heart, brain, and the kidneys are the most sensitive to ischemic events, which, when occurring in these organs, can be fatal.
So, what exactly is a stroke?
Some strokes can be categorized as being ischemic. As mentioned above, an ischemic stroke occurs when blood flow (and the associated oxygen supply) is restricted in an area within the brain, leading to tissue death. A major cause of ischemic strokes is a progressive disease called atherosclerosis, which can be translated to mean “the hardening of the arteries.”
Severe atherosclerosis of the aorta. Image Credit: Wikipedia.
Affecting the entire cardiovascular system, atherosclerosis is the result of cholesterol build-up inside of our blood vessels, causing their openings to become narrower. These cholesterol plaques can eventually burst, leading to the formation of a blood clot. Ischemic strokes occur as a result of a blood clot, medically known as a thrombus, that blocks the flow of blood to the brain, a phenomenon often related to complications from atherosclerosis. A ruptured cholesterol plaque and resulting blood clot can occur in the brain, or it can occur elsewhere in the body, such as in the carotid arteries, and then travel to the brain. Either way, the blood clot will block blood flow and oxygen delivery to sensitive brain tissue and cause a stroke.
Strokes that result from the bursting of a blood vessel in the brain can be categorized as being hemorrhagic. In this situation, there may be a pre-existing condition rendering the blood vessels in the brain defective, causing them to become weak and more susceptible to bursting. More often than not, a hemorrhagic stroke is the result of high blood pressure, which puts an awful lot of stress on the blood vessels. Hemorrhagic strokes are less common than ischemic strokes, but still just as serious.
How do you know if you’ve had a stroke?
The symptoms of a stroke can vary depending on which part of the brain is affected and can develop quite suddenly. It is common to experience a moderate to severe headache, especially if you are hemorrhaging (bleeding) in the brain. Other symptoms can include dizziness, a change in senses (hearing, seeing, tasting), muscle tingling and/or weakness, trouble communicating, and/or memory loss. If you are experiencing any of these warning signs, it is important to get to the hospital right away. This is especially important if the stroke is being caused by a blood clot since clot-busting medicationsare only effective within the first few hours hours of clot formation.
Once in the hospital, the caregiver will likely give anyone suspected of having a stroke a CT scan. From this test, doctors will be able to determine if you had a stroke, what type of stroke you had (ischemic versus hemorrhagic), or if there is some other issue. However, as was the case with my dad, a CT scan may not show evidence for a stroke. This issue can arise as a result of timing (test performed before brain injury set in) or size of affected area (too small to see). When not in an emergency situation, doctors may also or instead choose to prescribe an MRItest to look for evidence of a stroke.
If a stroke has been confirmed, the next steps will be to try and figure out the underlying cause. For ischemic strokes, it is important to find out if there is a blood clot and where it originated. Because my dad had an ischemic stroke, he had to undergo a series of tests that searched for a blood clot in his carotid arteries though ultrasound, as well as in the heart, using both an electrocardiogram(EKG) and an echocardiogram(ultrasound of the heart). The patient might also be asked to wear a Holter Monitor, which is a device worn for at least 24 hours and can detect potential heart abnormalities that may not be obvious from short-term observations, like those obtained via an EKG. If a stroke is due to a hemorrhagic event, an angiogramwould be performed to try an pinpoint the compromised blood vessel.
A stroke you did have. Now what?
Once a stroke has been confirmed and categorized, the patient will most likely be transferred to the stroke unit of the hospital for both treatment and further observation. If a clot has been detected, a patient will receive clot-busting medications (assuming this detection occurs within several hours of clot formation). Alternatively, a clot can be mechanically removed with surgery (animation of clot removal, also known as a thrombectomy). Patients might also be given blood-thinning medications to either ensure that clots do not increase in size or to prevent new clots from forming. As for secondary prevention, meaning preventing another stroke from happening, patients might be given blood pressure and cholesterol lowering medications.
If a disability arises due to stroke, a patient might need to undergo rehabilitation. The type and duration of stroke rehabilitation is dependent on the area of brain that was affected, as well as the severity of the injury.
Major risk factors and predictors of stroke
There are many situations that could predispose one to having a stroke, and many of these conditions are treatable. The absolute greatest predictor of a stroke is blood pressure. High blood pressure, also known as hypertension, will significantly raise your risk of having a stroke. Other modifiable stroke risk factors include blood cholesterol levels, smoking, type 2 diabetes, diet, alcohol/drug use, and a sedentary life style. However, there are also risk factors that you cannot change including family history of stroke, age, race, and gender. But that shouldn’t stop one from practicing a healthy lifestyle!
In conclusion, strokes are no joke. I am glad that my dad is still here (yes, dad, if you are reading this, we are in fact friends) and that he escaped with relatively no real consequences. Let’s just not do this again, ok?
Anti-coagulants:These are medications that help to reduce the incidence of blood clotting. The repertoire includes aspirin, Plavix, Warfarin, and Coumadin. Also called blood thinners.
Atherosclerosis:Literally translated as “hardening of the arteries,” this condition is hallmarked by the build-up of cholesterol inside of blood vessels. Atherosclerosis can lead to many complications including heart disease and stroke.
Cardiovascular System: The network of blood vessels and heart that works to distribute blood throughout the body.
Carotid Arteries: Arteries that carry blood away from the heart toward the head, neck, and brain.
CT Scan: Cross sectional pictures of the brain using X-rays.
Echocardiogram:An ultrasound of the heart. In stroke vicitms, electrocardiography is used to detect the presence of a blood clot in the heart.
Electrocardiogram (EKG or ECG): The measurement of the electrical activity of the heart. It is performed by attaching electrodes to a patient at numerous locations on the body, which function to measure electrical output of the heart.
Embolic Stroke: A type of ischemic stroke, an embolic stroke occurs when a blood clot forms (usually in the heart) and then travels to the brain, blocking blood flow and oxygen delivery to brain tissue.
Hemorrhagic Stroke: A type of stroke that results form the bursting of a blood vessel in the brain.
Hypertension:High blood pressure, defined as having 140/90 mmHg or above.
I finished assembling the requested cheddar cheese and cracker sandwiches and made sure to follow the precise directions for filling the sippy cups: half apple juice, half water, one ice cube, and a slice of lemon (don’t ask, my kids are high maintenance). Saturday afternoon was upon us and it was clear that we all needed a little downtime. So I set the girls up for a picnic on the family room floor, engaged Netflix, and laid out their snack. After a few minutes of getting comfy, calmness decided to pay us a visit. This was my carpe diem moment.
The perennial mint plant, known in my family as “El Jardin de Mojito.”
The weather could not have been more pleasant, and with the girls under the dear care of my best pal Pingu, I stepped out, barefooted, onto the deck. The sun caressed my cheeks. The wind whispered into my ear. The garden’s cologne was a reminder of my desire. Summer was seducing me and I did not could not resist.
I scanned the world before me, seamlessly moving my gaze from tree to tree, bush to bush, bird to bird, letting each thought morph into the next. I noticed the fluffy marshmallow clouds floating overhead and the sounds of a lawn mower humming in the distance. Then, at eleven o’clock, I caught a glimpse of the mint garden. The free flowing thoughts came to a screeching halt and my mind could focus on one thing and one thing only: Mojitos.
Belonging to the Lamiaceae family along with other aromatic herbs such as basil, oregano, and sage, mint has a tendency to spread rapidly and without care for the plants around it. But for us, this wasn’t an issue. Despite the vast culinary applications for this bountiful botanical, it is the quintessential ingredient for our favorite summer beverage, and so we’ve aligned ourselves with “the more the merrier” philosophy. After all, Greek mythology has dubbed mint as the “herb of hospitality” and what says “welcome to mi casa” more than the delicate sweetness of a cold mojito?
I didn’t bother to grab the scissors and made sure I followed the most direct route toward the mint patch. As I went to grab a large stalk, I noticed a little critter hanging out on one of the leaves. I lessened my grasp and began to examine the mint garden a bit more closely. It appeared to be a micro-ecosystem, bustling with tiny life forms.
Not wanting to miss a photographic opportunity, I ran back in, peeked in at the girls to make sure they were still there, and grabbed my camera (the good one). The snails were everywhere! My first reaction was “you best not be messing with the mojito garden!” But, upon closer inspection, these slow-moving, shelled cylinders of slime might be something more interesting, at least from a biological perspective.
Birds eye view of the European Amber Land Snail.
I knew that snails were mollusks, similar to clams and oysters, and that they could be further classified as gastropods, or “stomach foot” (to us, it looks like they are crawling on their bellies). But, I was having a hard time identifying the species to which these snails belonged, and that was probably because I was limiting my search to native species in NY State.
Frustrated, I turned to Ken Hotopp, conservation biologist and director of the environmental consulting company, Appalachian Conservation Biology. Ken informed me that these snails were amber land snails of the Succinea putris variety, which are native to eastern European countries and Great Britain, and further classified them as an invasive species.
Fred and Ethel, roaming the mint garden. Take a look at the “belly foot.”
When a species is classified as “invasive,” it typically means that they have high reproductive rates, can easily spread, and can quickly adapt to their new environment (a phenomenon called phenotypic plasticity). If these criteria are met, the invasive species can outcompete many of the indigenous species for resources and cause issues for the native habitat.
These snails probably made their way to the new world by hitching a ride on humans and despite the negative connotation associated with being an “invasive species,” it really isn’t their fault. They are just doing what they are biologically programmed to do: survive and pass on their gene pool to the next generation.
Regardless of origin, these snails looked beautiful to me. I love spiraling pattern at the rear of their calcium carbonate shells, and the way their tentacles, with eyes at the tip, scan their environment. It is really cool to watch the rhythmic motions of the foot, which can probably be plotted as a sine wave function in super slow motion.
Close up! Notice the patterns on the calcium carbonate shell, and the black eyes at the tip of the tentacles.
Realizing that time was of the essence (Pingu is effective for only so long), I zoomed out and started looking around for the best leaves to pluck. I said hello to the grasshopper that was probably banking on its green camouflage to keep it safe from predators, and took at look at the brilliant yellow flowers living atop the mint garden canopy. With the prize in hand, I ran into the kitchen, grabbed the simple syrup from the fridge (we always have some on hand), and began to make my mojito.
Within a few minutes, the finished product was in hand. But, alas, it would have to wait for I was being beckoned by the girls with the golden locks. I suppose one more episode of Pingu wouldn’t hurt.
I arrived at my building’s outpatient unit at 1:38 pm (I work in a hospital). Although my appointment was at 1:40 pm, I still gave myself a huge pat on the back for being “early,” which, technically, I was. A few signatures later, I was handed a paper gown of fairly decent quality and was instructed to wear it, opening to the back, after removing everything except my skivvies. There I was, sitting on the examination table, feeling quite vulnerable. And then I looked down. Crap! My legs were still in hibernation state. Even though doctors aren’t supposed to judge, I just didn’t see how this could fly under the radar. My only hope was that someone much more hairy had already been examined, setting some arbitrary threshold that would place me under “I’ve seen worse” category. Before my mind drifted into a state where I imagined every possible uncomfortable doctor-patient exchange, the doctor entered the room. It was a dude. I was a bit disappointed but there was nothing I could do about that. It was apparent that I was slightly embarrassed, and his attempt at making small talk did not help to dispel the awkwardness of having to let him scan every inch of my skin, including my you-know-what areas, for abnormalities. But I knew that this exam could save my life.
Skin cancer is the most common cancer in humans and comes in several varieties, including basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and melanoma. BCC is the most commonly acquired skin cancer, accounting for nearly 80% of skin cancers reported. As its name implies, BCC develops in the basal layer of the epidermis and often presents as a pearly, flesh colored nodule, usually on areas that get sun exposures (head, neck, arms). SCC, which arises in the squamous cell population of the epidermis, is the second most common type of skin cancer, affecting approximately 200,000 people each year, and often resembles a scaly patch surrounded by a red halo of inflamed skin. While sun exposed areas are more vulnerable, SCC can occur anywhere on the body (including genitalia) and, if not detected in a timely fashion, can spread to other areas in the body. The nastiest version of skin cancer is the potentially (and often) fatal melanoma. Either developing in a pre-existing mole or spontaneously appearing as a new dark spot on the skin, melanoma claims the life of one person per hour in the United States alone (including the life of my great uncle, Hank).
There are a number of misconceptionswhen it comes to skin cancers, such as the notion that people of color are less vulnerable. While an increase in the amount of the skin pigment called melanindoes provide more protection from the sun, the skin cancer survival rate for people of color is considerably lower than that of Caucasian people.This has mainly been attributed to a delay in detection, highlighting that everyoneneeds to undergo regular skin cancer screening procedures.Also, it is commonly thought that early signs of skin cancer should be painful.However, there are no symptoms associated with the development of most skin cancers and, other than visual signs, early skin cancer lesions can feel like normal skin.
The best bet is to be aware of the skin cancer risk factors, including sun exposure, family history, medical history, and number of moles, so that you can better protect yourself. Also, using water-resistant sunscreen containing both UVA and UVB protection (SPF 30 or greater), seeking shade whenever possible, and avoiding tanning beds, are great tactics for skin cancer prevention. Even if you follow all the rules, be sure to give yourself a periodic self-examination. Furthermore, get screened by a professional on an annual basis. Visit the American Academy of Dermatology to locate the free skin cancer screenings in your area.
Remember, even though you might have to bare your body to some random dude (with credentials), early detection is the key for survival. Plus, it’s all over in 5 minutes or less. I’d trade that for a healthy lifetime any day.