Biology Basics – What do you think you are?

Introduction

Who do you think you are?! Or more precisely, what? Most of us are familiar with the idea that we’re made up of about 65%[1] water, but what’s the rest of that all that squishiness? Most of the remainder (32.5%) is made up of molecules of proteins, fats, carbohydrates, and DNA, with some trace minerals and vitamins sprinkled in for good measure (2.5%).[2]

We’re a big Lego Millennium Falcon, made up of a collection of basic building blocks which are combined to form a larger whole. In our case though, we’re less foot-stabby Lego bricks, at the smallest scales, and more just a collection of atoms, which combine to form molecules, which in turn make up our cells, organs, and finally our body.

milleniumfalcon

Source: Lego.

Just like Lego, we can think of many of the major molecules of the human body as being made up of a limited set of small defined units (“monomers” – like the different coloured Lego bricks) which are then put together to build bigger structures (“polymers”), and finally combine to form you – the magnificent squishy Lego-like thing that you are. You may already be familiar with many of the main biological (as opposed to synthetic plastic) monomers and their polymer counterparts (Table 1).

monomer-polymers

Table 1: Cartoon examples of biological monomers and their corresponding polymers. Source: Edited composite by L.D.Nifty using geneticshbdanieldelprete.weebly.com (DNA) and Slideshare.net (protein, carbohydrates, fat).

We commonly see these terms in food and health news, but they’re not often discussed in the wider context of your body as a whole. You can find heaps of information all over the internet covering the basic biology, so hopefully what this post will achieve is bringing it all together to help you decode your reading material.

I’ve used a mixture of cartoons and more detailed chemical structures together to hopefully unite different representations that you might have seen out in the world, although any feedback on how to make this clearer is always welcome. And don’t be scared of the chemical structures … they really very friendly.

Making the Most of Yourself

DNA

DNA (deoxyribose nucleic acid) only makes up about 0.1% of our body by mass, but it’s one of the most important molecules we have, providing all the instructions for your cells by telling them which proteins to make; it’s basically your operating system – the Microsoft Windows of the cell. DNA is that familiar spiral (double helix) polymer which is made up of “nucleotide” monomers (Figure 1). The nucleotide monomers (also called bases) are made up of three parts: a phosphate group, a sugar, and one of four nucleotide bases: adenine (A), cytosine (C), thymine (T), guanine (G).

nucleic acids

Figure 1: General structure of single stranded DNA showing the four possible DNA nucleotide bases.

Long strands of DNA are made up of millions of nucleotides connected along the sugar-phosphate backbone with the nucleotide bases sticking out the side. These bases can pair up with their matching buddies – adenine (A) with thymine (T) and cytosine (C) with guanine (G) – to give double stranded DNA. (Figure 2). This then all twists up giving that familiar double-helix structure we remember from Jurassic park (just without the googly-eyes). We often see DNA reported in news stylistically as coloured shapes, letters, or just as connected lines for simplicity (as seen below).

dna_base pairing composite

Figure 2: Matched DNA base pairs (left) and formation of a DNA double helix structure (centre). Example of stylized DNA (right). Source: L.D.nifty edited composite using imagines from basicknowledge101, geneticshbdanieldelprete.weebly.com, divineerror.deviantart.com

DNA, like other biological polymers (e.g. proteins and carbohydrates) are broken down and metabolised in the stomach and gut when we eat them so that our body can use the resulting monomers to build its own DNA.[3] It’s generally for this reason that you don’t have to worry about DNA from genetically modified organisms (GMOs) as it all gets digested in the stomach and gut, and doesn’t interact with your own genetic material in your cells.[4] Not that it would be dangerous anyway.

Proteins

Just for gym junkies? Nope! Proteins are a hugely diverse group of polymers which do pretty much all the work in the body, making up at about 20% of its mass.[1] Proteins move stuff around the cell, provide structure and scaffolding to hold things up, and they speed up (catalyse) chemical reactions to make your metabolism possible; we usually call these last type of proteins, enzymes.

protein

Source: how2getbig.com

Proteins come in all shapes and sizes, but are a bit like a tangled-up ball of Christmas tree lights. However, instead of being made up of lots of little different coloured lights, proteins (the polymer) are long chains of amino acids (the monomers) (Figure 3), which we sometimes call peptides when they’re in their straight un-tangled/unfold form. The big difference is that your proteins work much better in their tangled-up form and unsurprisingly they don’t take kindly to being jammed into an electrical outlet – and neither would you, I’m sure.

How a protein is tangled up is key to its ability to carry out its job as it allows it to interact with different molecules (substrates) in very specific ways. Temperature, acidity (pH), and other factors can cause proteins to un-tangle (denature) or change their shape so they no longer work properly. Thus, your body puts a lot of effort into making sure these factors are tightly controlled. This is why claims of alkalinity diets are so thoroughly debunked because your body is set up to stop this un-tangling from happening lest you unwrap all your lovely proteins.[5] No one wants to be a mushy heap on the floor.

protein from amino acids composite

Figure 3: Cartoon of amino acid monomers combining to form a peptide polymer and then folding to form a protein (left). And, chemical structures of two amino acids (with variable side chains, R) combining to form a peptide (right). Source: L.D.nifty edited composite using imagines from Juicing for Health & Wikimedia Commons.

Amino acids have two parts: a peptide backbone, which is shared generally by all amino acids; and a variable side chain (represented above by the different colour circles (Figure 3, left) or the R group Figure 3, right). These variable bits give each amino acid their unique chemical and physical properties which they impart on the proteins they end up in – this is how we can get such a huge number of different proteins from a smallish number of starting amino acid monomers (Figure 4).

Us humans make our proteins from 20 essential amino acids which we get from our diets, but sometimes our bodies edit these or makes a few from scratch if we’re in the mood for something a bit spicier (Figure 4).

20-Common-Amino-Acids-v3

Figure 4: The 20 essential amino acids. Source: Compound Interest

So… now you have some lovely proteins: maybe some haemoglobin to transport oxygen around your body, some collagen to give structure to your skin and hair, some alcohol dehydrogenase to break down your last glass of wine, and some dopamine receptors in your brain to make you feel good. But where’s the energy for all this work coming from?

Carbohydrates

Yay, another polymer. All these polymers and we’re starting to sound more like a plastics factory than a person. This time though it’s carbohydrates. Associated with grains, breads, starchy vegies, and fibre, carbohydrates are polymers made up of sugars monomers. Our bodies are pretty good at breaking down (hydrolysis) the carbohydrate polymers to release their sugary goodness which we can then use for energy. In fact, our brain prefers to use sugars for its energy as the biproducts of sugar metabolism are less toxic than those for fats, proteins, or alcohol metabolism.[6] Not all complex carbohydrates can be broken down when we eat them however, but we can use them to help our gut health; these include types of dietary fibre.

carbs pic1

Source: Youtube.

Like so much in bioogy, we can’t escape a quick note on naming. Carbohydrates include all sugary based molecules and are classified as “saccharides”. Simple monomers of sugars are called monosaccharides and include glucose and fructose (Figure 5, a). Bonding two monosaccharides together gives us a disaccharide, everyday examples including common table sugar (sucrose) made from glucose and fructose, and the common dairy sugar, lactose is made from glucose and galactose (Figure 5, b). We can also connect heaps of monosaccharides together in long chains or as branching trees to form polysaccharides (aka complex carbohydrates), e.g. glycogen, which our body uses to store sugars for later use (Figure 5, c).[7]

carbs - sugars to carbs

Figure 5: Examples of simple sugar monomers (a), simple polymers (b), and complex carbohydrates (c). Source: L.D.nifty edited image from Thinglink.

While we can make some sugars like glucose from amino acids, we get most of our carbohydrates from plants, made from carbon dioxide (CO2) via photosynthesis. In our body’s, complex carbohydrates are broken down into their simple sugars which are then used by our cells for energy. One of the biproduct of this is carbon dioxide which we then breath out.

You might have come across the term glycemic index (GI) in your travels when people talk about carbs in your food. In general, GI a measure of how quickly different carbohydrates will increase your blood sugar. Simple sugars can spike your blood sugar quickly (high GI) while complex carbohydrates take time to break down (low GI). Eating mostly low GI foods is encouraged to promote a steady, continuous supply of energy throughout the day, as opposed to a nasty sugar crash, and so it can be a useful tool when trying to decide a ‘good’ food from a ‘bad’ food. However, GI does not take into account things like nutrient content and like so many things to do with diet, it can get a lot more complicated depending on exactly what you’re eating and in what combination.[8]

glycemic-index-chart

Source: Buck Wheat Health.

Fats

Oh, they’re so tasty! And we’re all well aware of how good our body uses fats to store energy. But fats and oils (also called lipids) also help make up the bulk of the walls of our cells (cell membranes) giving them structure. They also include cholesterol, steroids, and many hormones. We can think of our body’s cells as essentially fat bubbles that we’ve filled with those lovely proteins from earlier to do all the work with some sugar for energy. So, fats and oils are pretty essential at keeping you healthy, but not all fats are created equal. Some food sources are more nutrient rich than others making fats and oils probably one of the more misunderstood of the big nutrient groups.

fats

Source: Fitness Magazine.

Fats and oils are both types of a larger category of greasy molecules called lipids and are usually not talked about in terms of monomers and polymers in the same way that proteins or carbohydrates are as they’re not long chains of repeating units. The ones important for diet and our cell membranes are generally made up of a molecule of glycerol with a number of long chain fats (fatty acids) bonded together (Figure 6).

fat - triglyceride

Figure 6: One molecule of glycerol bonding to three molecules of a saturated fatty acid to give a triglyceride fat (kind of “polymer”-like). Source: L.D.nifty edited imagine from R D Feinman on WordPress

The big difference between fats and oils is akin to that between a nun and a hooker – that is to say, kinkiness. Oils (also known as unsaturated fats) have ridged bits (double bonds) along their carbon backbone making the chain kink and meaning the molecules don’t stick to each other very well (Figure 7). This makes them runny, gives them lower melting temperatures, and means your body treats them differently when you eat them. Fats (saturated fats) don’t have these kinks as so can stick together very comfortably and usually have higher melting temperatures and are often more solid(ish).

fats - different types

Figure 7: Example of a saturated fat (left) and a cis-mono-unsaturated fat (right). Source: L.D.nifty edited image from The Healthy Butcher.

Depending on where in the world you’re living, some of heavily processed food may also contain artificial trans fats (trans-unsaturated fats). They differ from naturally occurring cis-unsaturated fats (e.g. oils) in that their kinkiness goes the other way – that is, the double bond makes them bend in a different direction than your body is keen on (Figure 8).

fat trans

Figure 8: Examples of a saturated (left), ‘natural’ unsaturated fat (center), and a trans fat (right). Source: L.D.nifty edited image from Chemistry Stack Exchange.

While unsaturated fats are typically considered ‘healthier’[9] compared to saturated fats, trans-unsaturated fats (sometimes also called partially hydrogenated fats) are banned from sale in many countries due to serious health concerns, including causing an increase in ‘bad’ LDL cholesterol, development of heart disease, and other nasty things suggested by the research.[10] Now, just because something is ‘natural’ or ‘artificial’ doesn’t mean it’s good or bad for the body…but in this case, we did done bad, ya’ll and trans fats should probably be avoided. SciShow’s YouTube Channel has a great little video if you’re keen for a more detailed run through on fats.

The WHO recommends no more than 1% of our fat intake should be trans fats.[11] Here in clean green New Zealand it’s estimated that the average intake is about 0.6% but manufacturers don’t have to declare how much is in their products. By 2015, six European countries had already banned trans fats, while many more had agreed on a plan to eliminate them from food by 2020.[12] Various other countries, like the USA, have worked towards either bans or an increase in labeling for trans fats.[13]

fat trans pic

Source: 123RF.

Add a Sprinkle of this and a Dash of That

We’ve covered off the major molecules that make up our diets and bodies, but there’s still a fascinating grab-bag of other compounds and ions which are essential to keep you chugging along. If you’ve got this far though I’ll not keep you too much longer. There’s heaps I could say about the remaining components of the human body, but I’ll just provide some quick additional references if you’d like to delve more deeply:

Vitamins: collection of small unrelated organic compounds which are involved in a lot of different chemical reactions in your body. Some help enzymes catalyse metabolic processes (co-factors) or act as anti-oxidants (e.g. vitamin C).

Trace Minerals: Chemical ions essential for normal cell function. Calcium (Ca2+), phosphorus (as phosphate, PO43-), potassium (K+), sodium (Na+), and magnesium (Mg2+) are the major minerals. Common minor trace elements include: sulfur (often as sulfate, SO42-), iron (Fe2+ and Fe3+), chloride (Cl), cobalt (in vitamin B12, Co2+), Zn(2+), manganese (Mn2+), molybdenum (as molybdate, MoO42-), iodide (I), and selenium (Se). These are ‘inorganic’ ions and compounds[14] in contrast to ‘organic’ compounds: technical terms that don’t have anything to do with how “natural” or ”synthetic”, good or bad, or biological they are; an organic compound is simply one that contains carbon (C).

vitamins-and-minerals

Source: Progentra.

Cholesterol & Steroids: Steroids are a type of lipid (fat) and include some hormones and cholesterol. Cholesterol is important in building cell membranes, but when we talk about it in a health and dietary context it’s all the same molecule. It’s how its packaged up and transported around the body that’s important.[15] If it’s in the form of LDL (low-density lipoprotein) it’s considered a source of ‘bad’ cholesterol and promotes the build-up of plaques in arteries which can result in heart disease. HDL (high-density lipoprotein) is known as the ‘good’ cholesterol, but a healthy person actually has a balance of both so you see it reported as a ratio. Low fat diets, weight loss, and medications can be used to maintain healthy levels of cholesterol.

Hormones: a diverse category of molecules which are sent throughout the body via the blood and lymphatic systems to control lots different functions. Examples include: Insulin (a peptide) used to control blood sugar levels; estrogen (a steroid) which controls sex characteristics but also affects bone formation and metabolism; and the neurotransmitter dopamine (small molecule) used to control mood.

Cells and bone: All these molecules above come together to form your cells and in fact the cells of all life. Everything on earth shares the same basic building blocks which is expected when all life shares a common evolutionary history over the last 3.5 billion years. Cells then come together to form tissues, then organs, and finally you. The only big bit we haven’t really touched on is the hard stuff: bone – essentially a mix of an inorganic mineral called hydroxyapatite (a calcium phosphate (Ca5(PO4)3OH salt) with proteins like collagen mixed in.

Final Thoughts

So, there it is; that’s what makes you, you – at the smallest Lego brick level anyway. I’ve focused on the molecule level cause that’s what we so often see talked about in news and blogs about what’s in our food and how it’s affecting our health. Also because biochemistry is awesome! There’s obviously a whole world of cell biology and physiology out there we could dive into, but we’ll leave that for another day. If there’s anything you think should be added, edited, or that needs to be made clearer I’m more than happy to keep this post active overtime as a tool to future superfoods and health blog posts. Hopefully I’ve achieved my goal of showing how all these biological terms relate to each other and helped you decode your next health or food read. An if all else fails, remember you’re just basically squishy Lego.

lego


Source:
Lego.

References and Sources

[1] 65% water by mass, but 98% water by number of molecules. Percentages of soft, non-bone components.
[2] Freitas Jr., R. A. Nanomedicine. 1999. Landes Bioscience. Tables 3–1 & 3–2. ISBN 1-57059-680-8.
[3] Exposure to Environmental Hazards: http://enhs.umn.edu/current/5103/gm/absorb.html. (accessed: October 6, 2017).
[4] Liu, Y.; Zhang, Y.; Dong, P.; An, R.; Xue, C.; Ge, Y.; Wei, L.; Liang, X. Digestion of Nucleic Acids Starts in the Stomach. Nature: Scientific Reports. 2015. 5, 11936.
[5] Healthline: https://www.healthline.com/nutrition/the-alkaline-diet-myth#section7. (accessed: October 6, 2017).
[6] Brain Facts: http://www.brainfacts.org/about-neuroscience/ask-an-expert/articles/2012/how-does-the-brain-use-food-as-energy/. (accessed: October 6, 2017).
[7] Berg, J. M.; Tymoczko, J. L.; Stryer, L. Biochemistry. 5th edition. Chapter 21: Glycogen Metabolism. New York: W H Freeman, 2002.
[8] NZ Nutrition Foundation: GI – Glycaemic Index. https://www.nutritionfoundation.org.nz/nutrition-facts/nutrition-a-z/gi-and-gl. (accessed: October 6, 2017).
[9]  In general, cis-saturated fats are considered ‘healthier’ although this is hugely complicated depending on type, dietary source, and use in the body, and the research is not as conclusive as it once was.
[10] W. C., Willett; A., Ascherio.  “Trans fatty acids: are the effects only marginal?”, American Journal of Public Health. 1994. 84, 5. 722-724.
[11] Food Standards New Zealand. http://www.foodstandards.govt.nz/consumer/nutrition/transfat/Pages/default.aspx. (accessed: October 8, 2017).
[12] WHO Europe. http://www.euro.who.int/en/health-topics/disease-prevention/nutrition/news/news/2015/09/eliminating-trans-fats-in-europe. (accessed October 8, 2017).
[13] Tavernise, S. F.D.A. Sets 2018 Deadline to Rid Foods of Trans Fats. The New York Times. https://www.nytimes.com/2015/06/17/health/fda-gives-food-industry-three-years-eliminate-trans-fats.html. (accessed: October 8, 2017).
[14] Some of these ions are also found incorporated into organic (carbon containing) compounds making them “organometallic metallic” or “coordination” compounds.
[15] Heart Foundation of New Zealand. https://www.heartfoundation.org.nz/wellbeing/managing-risk/managing-high-cholesterol. (accessed October 8, 2017).
Header source: youtube.com

 

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