DXS Op-Ed: How birth control can save the world

By DXS Biology Editor Jeanne Garbarino

Over the last few months, the concept of birth control has been under great scrutiny in the American eye.  Many politicians have been discussing it’s “moral” implications, and whether institutions or organizations should have the right to deny insurance coverage for hormonal contraception if it does not fall within the confines of their belief systems.  And while American women have narrowly escaped legislation that would impede their reproductive health and freedom, politicians, mostly men, feel it necessary to make misinformed or even completely false statements about birth control. 

For some strange reason, there is this erroneous idea that birth control is not a matter of health, but rather a means by which a woman can engage in careless and frequent sexual activity, with a man, and without the consequences of pregnancy.  It’s clear that the picture these politicians are trying to paint is that of debauchery and immorality, which, of course, is a departure from the puritanical integrity they embody.  But, rather than focus on this utter nonsense, I would prefer to highlight the significant impact birth control will have on the future of our civilization and our planet.

The human population has grown steadily since the beginning of our species.  However, the rate of growth began to skyrocket after the industrial revolution, and our population has actually doubled over the last 50 years, reaching 7 the billion mark in March of this year.  This is an astounding statistic since it took until 1804 – around 50,000 years – to reach our first billion. 

World Population: 1800 – 2100 (Wikimedia Commons)

What makes these numbers really scary is the concept of carrying capacity, which is an ecological term used to describe the maximum number of individual members of a species that a certain habitat can support.  In this case, the species is human and that certain habitat is planet earth. 

Here’s the thing: the availability of our resources will not match the rate of population growth.  Given our current technologies, there is only so much food we can grow, only so much water we can drink, only so much space we can inhabit, only so much waste we can safely rid, only so much energy we can harness.  There will be a point that the human population will hit its carrying capacity on earth, and when it does, the chances of widespread famine will be great, and the delineation between the developing world and the developed world will be no longer.  

Given this very serious issue, Britain’s Royal Society has recently convened to discuss the future of the human population and on April 26th, 2012, and published their findings in the People and the Planet Report [PDF].  For me, key findingnumber three struck a cord:

Reproductive health and voluntary family planning programmes urgently require political leadership and financial commitment, both nationally and internationally. This is needed to continue the downward trajectory of fertility rates, especially in countries where the unmet need for contraception is high. (emphasis theirs)

Political leadership and financial commitment – Did you see that, American politicians??  For those of you who are unnecessarily waging war on women’s reproductive rights, its time to get your giant heads out of your collective asses and realize the implications of legislation that would go against ensuring both the continued success of our species and the health of our planet.  It is time to stop spending money on these regressive and oppressive campaigns guised under the false pretense of “religious freedom” and start making a financial commitment to the women (and by association, men) who live in our nation.

To drive this point even further, here is another excerpt from the People and the Planet Report (my favorite bit, found in Box 2.5 on page 33):

Women bear the main physical burden of reproduction: pregnancy, breastfeeding and childcare. They also bear the main responsibility for contraception as most methods are designed for their use. Men, it may be argued, reap the benefits of children without incurring an equal share of the cost. It follows that women may be more favourable to the idea of small families and family planning than their partners but unable to express their inclinations in male-dominated systems. Such views received international endorsement in the Program of Action resulting from the UN conference on population in 1994. Paragraph 4.1 states that “improving the status of women is essential for the long-term success of population programs”.

We currently live in a nation where 99% of women who are of reproductive age have used some form of birth control at least once.  And when it comes to hormonal contraception, over 80% of sexually active women aged 15-44 have relied on “the pill” as a means to prevent unwanted pregnancies.  This has contributed to an average of two births per American woman, which is considered to be the replacement rate for a population.  Compare this number to countries where birth control and reproductive education is scarce – countries like Niger (7.52 births per woman) or Afghanistan (5.64 births per woman) – and one can see the impact of family planning through contraception.  Furthermore, it has been well documented that women in developed worlds who are provided with the means to control their fertility are more empowered and their families are healthier.   

While our situation in the US is significantly better compared to underdeveloped nations where rape and the cultural devaluing of women is commonplace, we still have a responsibility to uphold – a responsibility that would undoubtedly increase the quality of life for women (and men), as well as contribute to the overall health of the human population.  Why would we want to go backwards and remove the ability of a woman to decide when, if ever, she would like to reproduce? 

Having access to birth control empowers women and allows them to make greater contributions to society.  And because contraception is primarily the responsibility of a woman, our society needs to ensure that birth control, reproductive education, and family planning resources are readily available to EVERYONE.

The United Nations predicts that the ten-billionth person will be born around 2050.  Will we continue to fight this ridiculous fight against women’s rights or will we redirect our collective energy to developing technologies that will help our species and planet better cope with the increasing demands associated with a steadily rising population?  Let’s stop allowing stupidity to prevail and let’s start doing the right thing: making sure that birth control is readily available to any woman who wishes to use it.  Because, now more than ever, it is clear that birth control will save the world.   

Note: In my readings for this article, I came across a wonderful resource for anyone interested in learning more about human fertility and population growth.  Through the wonders of the internet, Academic Earth is offering a free (!) online course called Global Population Growth, given by Yale University professor Robert Wyman. 

These views are the opinion of the author and do not necessarily either reflect or disagree with those of the DXS editorial team.

Biology Explainer: The big 4 building blocks of life–carbohydrates, fats, proteins, and nucleic acids

The short version
  • 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.

Nucleic Acids

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.

 By Emily Willingham, DXS managing editor 
This material originally appeared in similar form in Emily Willingham’s Complete Idiot’s Guide to College Biology

NOC: A whale of a mimic

Listen to this:

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What does it sound like to you? (Recording courtesy of the BBC.)

If you thought it sounded human, you’re right. It does. But that’s not a human making the sound–it’s a beluga whale named NOC.

Shh. The beluga is listening.
Credit: via Wikimedia Commons.
Dolphins have been trained to mimic people, but the fellow in this recording apparently picked up human-sounding lingo on his own. Researchers describe his acquisition as self taught. According to this BBC story, the way the white whale pulls it off isn’t easy–he had to really work at it in a pretty un-beluga-like way to get his voice so much lower than the normal beluga vocalization. You can listen to the typical beluga talk, which sounds like a dyspeptic piglet trapped by a creaky door here. It sounds. Ed Yong at Not Exactly Rocket Science tells us these whales are sometimes called “sea canaries” but that they usually sound like children in the distance.

To me, this human mimicry sounds like nothing as much as men on a fishing boat, hollering at each other over the wind, just as they might sound to ears underwater. In fact, the way the researchers found NOC, according to the BBC story, was when a diver surfaced, thinking he’d heard someone tell him to get out. 

What do you think it sounds like?

Friday Roundup: 2011 top science lists, radium laced condoms, and the clitoris

A Double X Science grandma showed us this picture.
We thought it was the most ridiculously cute thing we’d seen all year.

As 2011 draws to a close, media outlets and science bloggers have busily collated their top-10 (or 12 or 20) lists of science-related cool/interesting/freaky/fantastic stuff this year. Here’s a selection that should keep you busy for about the first half of 2012:


Health ‘n’ stuff

  • Do you know the clitoris? Not many people really do. Read this. It’s important information, not to mention mindblowingly cool.
  • Put the toilet seat lid down when you flush. Please.
  • Emily Willingham, Double X Science managing editor, is also an editor on a new book just out, The Thinking Person’s Guide to Autism. Consider buying a copy to leave in your pediatrician’s office or to donate to your local library.
  • Once upon a time, people made condoms that glowed in the dark, thanks to radium. Yikes.

Sciencey fun!

Friday Roundup

[Image via Flickr, John Philip Green. Don’t know if he’s one of the mullets or not.]

Do fecal bacteria from face mites cause rosacea?

Image via Wikipedia. License
Back when I taught college general biology, I always gave a lecture in which we talked about ecosystems. At the beginning of the lecture, I showed them the above image or a similar one and explained that the handsome organism it features lives quietly and unobtrusively in the hair follicles on your face. My goal was to combine horror and information so that my students would never forget that they, too, are ecosystems–and, I hoped–get acclimated to the idea. Most of them just seemed pretty creeped out.

The animal above is a mite and member of the Demodex genus. Because of its affinity for follicles, it’s known as Demodex folliculorum. Its partner in existence on your face (and some other places) is the shorter version, known as Demodex brevis [PDF], which is drawn to your sebaceous (oil) glands, also on your face. Because they have “piercing-sucking mouth parts,” pedipalps, and eight legs in four pairs, according to one lovingly detailed description in a 1976 paper, they are arachnids, just like spiders. Tiny arachnids that live on your face, taking moonlit strolls when it’s dark and diving for cover in light. They live there, just as you live in a house, except your face is like an array of microscopic cave houses where these organisms reproduce and eat. And apparently are rather active; from a 1985 paper about these mites and what they do on your eyelids:

The normally torpid existence of demodectic mites of the eyelid changes with the onset of oviposition (egg laying). There occurs a burst of activity characterized by flexion, extension, and rotation.

In addition to all of flexing and extending and rotating, these mites also happen to die on your face. They “disgorge” products from their salivary glands while alive, but when dead, they appear to disintegrate, releasing the contents of their guts onto you and the visage you show the world. As it happens, the mites themselves are, like you, hosts to unseen organisms, in this case the bacteria in their guts.

The word on the street–and in this paywalled paper–is that these mites don’t have anuses. Thus, after suffering from a near-lifelong (a few days at most) case of constipation, they die and unconstipate all over you. 

If the idea of dead mites reproducing and dying and disintegrating all over your face didn’t do you in, congratulations. You’re a rational person resigned to your inevitable fate as an ecosystem. Either way, you may have wondered: What does this mite-y fecal matter do to my face?

Experts have disagreed about what these mites and their, er, exudants do to their host, but studies have found links between their presence and abundance and several dermatological and other diseases. Among these, rosacea is possibly the best known, in part because it is relatively common (up to 3% of people worldwide have it) and easy to spot: It produces a pronounced redness of the skin, sometimes with a sandpapery look, and with age and as it worsens, can result in manifestations like bumps on the skin and gritty eyes, including effects on the nose like those in this painting:
A nose with features of end-stage rosacea (left).
Public domain, via Wikimedia Commons.
Indeed, as we age, the population of these mites grows, and rosacea is considered a chronic condition that crops up most often between the ages of 30 and 50 or 60. It also has had an air of mystery about it, including why some people develop it and others do not, and what, exactly, causes it. Now, researchers who have conducted a deep review of all of the rosacea-related research suggest that it’s primarily a bacterial infection. The source of the bacteria? That mite poop. 

Does that mean that people who don’t have rosacea are in some way less fecally affected than people who do? Not necessarily. These mites are “commonly” found on people without any outward manifestation of effect. But people with rosacea may develop it thanks to wonky immune systems that underreact or overreact to the mites or the bacteria in their poop, according to the authors of the review, published in the Journal of Medical Microbiology. 

In other words, people who have rosacea might actually be fighting the mites and their poop contents harder than people without it, so no need to feel all superior if you’re rosacea free. Rosacea is more common in women than in men, which is in keeping with a general female prevalence of disorders of immune wonkiness. Also, just in case menopause didn’t carry enough baggage, rosacea happens to strike women “particularly” during that time our ovaries are saying their sayonaras.

One of the bacteria in question actually might begin as just another resident lurking in the ecosystem that is your skin. The mites eat the bacteria along with the delicious (I’m assuming) skin cells they consume. When the mites die and disintegrate, bacterial bits may emerge along with other components of the mite digestive contents. It is possible, say the review authors, that these bacterial bits–like lots of other bacterial bits–trigger an immune response that we see as rosacea. Indeed, one antibiotic, doxycycline, that’s particularly well known for conquering this bacterium, is reasonably effective for rosacea.

What can you or any of us do to prevent or treat rosacea? As far as prevention, the review authors note that in some cases, a genetic immune wonkiness may predispose some people to developing it. Because these mites often are deeper than skin surface, techniques like exfoliation are unlikely to be helpful. As science writer Ed Yong cautions in his fantastic piece about this review paper, do not try to bleach your face, either. Current treatment consists of a topical medication to reduce inflammation and oral antibiotics. In severe cases, a medication used for cystic acne and that actually inhibits sebaceous gland secretion is a possibility.

Do you or does someone you know have rosacea? What treatments have you tried? Given the potential involvement of a wonky immune system, have you noted any co-occurrence of other immune-related problems?