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Elemental building blocks of biological molecules

Common elemental building blocks of biological molecules: Carbon, Oxygen, Hydrogen, Nitrogen and Phosphorus.

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  • leaf orange style avatar for user Learn
    When we say something like the body is 65% oxygen, what does that mean? Does that mean 65% of atoms in the body are oxygen atoms? 65% of our weight? Thank you!
    (10 votes)
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    • blobby green style avatar for user gm
      I think it would be safe to assume that our body is 65% oxygen by mass.

      In general, our body is 65-70% water by mass. Water has a molar mass of 18 g/mol, and the majority of that mass comes from oxygen, not hydrogen (oxygen molar mass = 16 g/mol). 16/18=89%, and if 70% of body weight is water, than 70%*0.89=62.3% of body weight is oxygen. However, water is not the only source of oxygen; considering oxygen from other body organs as well, our body would be approximately 65% of oxygen by mass.

      Also, as you can see from hydrocarbon chains of macromolecules, there are a LOT of hydrogen atoms attached. To calculate percentage of number of oxygen atoms, the formula would be:
      (oxygen atom number) / (total atom number)
      However, hydrogens would make total atom numbers increasingly large, so it would be difficult for oxygen to take up 65% of the number of atoms.

      Of course, all these calculations came up from my head...since there isn't any reference for this, it would be better to ask your science teachers if anyone sees this.
      (16 votes)
  • blobby green style avatar for user kfraz
    Hello, I have what might be a stupid question.
    I understand how to tell which functional groups molecules have. How do I use those to determine what type of molecule it is? (protein, nucleic acid, carbohydrate, phospholipid, etc.)
    (11 votes)
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    • stelly blue style avatar for user Komphiikatt
      Carbohydrates are made up of C, H and O. The ratio of H:O is 2:1. An example for this is glucose (C₆H₁₂O₆).
      Lipids are made up of C, H and O. However, the ratio of H:O is >2:1.
      Proteins are made up of C, H, O, N, P and S. The units which make up proteins are known as amino acids. These amino acids are made up of an amino group (-NH2), a carboxyl group (COOH) and a unique "R" (side chain) group. The side chain (R) can differ based on the type of amino acid.
      Nucleic acids are made up of C, H, O, N and P. The units which make up nucleic acids are known as nucleotides. Nucleotides consist of a sugar (such as deoxyribose for DNA and ribose for RNA), a phosphate group, and nitrogenous bases (adenine, guanine, cytosine, thymine) [Uracil is present instead of thymine in RNA].

      Hope this helps :)
      (9 votes)
  • starky tree style avatar for user Tilak Patel
    What is a biological system and molecules in simple terms? Im pretty confused in understanding what Sal explained. Thanks in advance!
    (5 votes)
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    • duskpin ultimate style avatar for user Aria
      Biological system: think everything from your nervous and digestive systems, to a cell in your body. Basically anything that has a way to maintain itself and its functions.

      Molecule: is a group of two or more atoms. Think water molecules H2O.

      The molecules in this video are specifically *macromolecules*, DNA, amino acids, ATP, etc. are the macromolecules that build up the human body and every complex living being (So all life today other than bacteria). They are made of a lot of atoms, and they can repeat in chains, which is why they are called "macro"molecules = large molecules.
      (6 votes)
  • boggle blue style avatar for user x.asper (bio)
    I see some of these trace elements are the same used in energy drinks. Is too much of these trace elements dangerous for your health?
    (4 votes)
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    • aqualine ultimate style avatar for user Sriram
      Since our bodies cannot naturally synthesize these elements we must consume them in our diets. But, to answer your question, too much of it just like many other good things, is bad for you. In this case, excess consumption could result in toxic side effects.
      (7 votes)
  • aqualine seedling style avatar for user berrypotato
    how come O makes up 65% of our body and hydrogen makes up much less when H2O is made up of 2 H and only 1 O?
    (4 votes)
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  • blobby green style avatar for user MarkD
    At 3.19 Sal says Carbon makes up about 0.04% of our atmosphere. doesn't he mean CO2? if so carbon would make up an even smaller percentage around 0.01%
    (4 votes)
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  • blobby green style avatar for user Danielle  C.
    How many types of elements can be found in bio molecules ?
    (2 votes)
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  • blobby green style avatar for user Cat lover
    When Sal mentioned Triglyceride, he called it a 'fat', but wouldn't one of the components of Triglyceride be glycerin or glucose? Just intrigued :)
    (1 vote)
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  • eggleston blue style avatar for user C5LOwenZ
    If water is two parts hydrogen and one part oxygen, why does oxygen have such a disproportionate ratio in the body? It doesn't seem to show up in as many other compounds as carbon and hydrogen, and it also seems to me that the word percentage implies that mass takes on a secondary importance.
    (1 vote)
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  • blobby green style avatar for user Cat lover
    So are the elements always colour coded? Do they need to be a specific colour to be identified, or can they be recognised by their structure?
    (1 vote)
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Video transcript

- [Instructor] What we have here is just a small sample of the types of molecules that you will see in a biological system. At the top left right over here, you have an example of an amino acid. Amino acids are the building blocks of proteins. And if we were to take a look at what an amino acid is made up of, in this dark gray color, those are carbon atoms, in the white, you see hydrogen atoms, in the red you see oxygen atoms, and this blue right over here, that is a nitrogen atom. And as you can see, a lot of these elements keep showing up in these various molecules, especially carbon and hydrogen, but also you see a lot of oxygen and nitrogen, and as we're about to see, phosphorous also pops up a lot. Now this isn't a comprehensive list, you'll also see other elements, but these tend to show up fairly frequently. For example, this is a model of ATP, adenosine triphosphate, as we study biology, you'll see that it's often viewed as the currency of energy, the molecular currency of energy in biological systems. And once again, we see a lot of carbons in the dark gray, we see the hydrogens in this off white color, or the light gray I guess you could say, you see your oxygens again, here the nitrogen is in this light blue color, and then you see the phosphoruses right over there in that yellow color, phosphorus. This is a model of a triglyceride, often known as a fat molecule, fat molecules are used for energy storage, and once again, you see many carbons in the dark gray, and then you see these hydrogens, and then a few oxygens. This is a model of DNA, a small segment of DNA, and this is a much more complex molecule than the other ones we've seen, in fact, this could extend far beyond our screen in either direction. But once again, you see these same familiar elements. You see the carbon in the dark gray, the hydrogen in that white color, you see the oxygens in the red, the nitrogens in the blue, and the phosphorus in the yellow. So the big takeaway here is that biological molecules tend to be made up of the same set of elemental building blocks, and in fact, it isn't just at the elemental level, it can even be at the molecular level. For example, in ATP you have what's known as a nitrogenous base right over here, you have a five carbon sugar right over here, and you have three phosphate groups, or a triphosphate group. In DNA you have something very similar, the nitrogenous bases are hard to see, they're kind of the rungs of the ladder here, you have your five carbon sugars, also hard to see, and then you have these phosphates as well. In fact, the backbone of DNA is made up of these five carbon sugars and these phosphates. Now why do these elements keep showing up? Well these are elements that you will see a lot in Earth. For example, nitrogen makes up most of our atmosphere. We have a lot of water on the surface of our planet, which is made up of oxygen and hydrogen. Carbon actually makes up a surprisingly small percentage of our atmosphere, about 0.04% of our atmosphere, but photosynthetic organisms, like plants, are good at fixing carbon and storing energy in carbon bonds, and when we eat those, those become part of our bodies. And just to get an appreciation of what we are made up of, in terms of elements, we can look at this chart right over here where we see that we are primarily made up of oxygen, percentage in body, and that's because we're primarily made up of water and water is primarily oxygen. It also has hydrogen. Now second to oxygen is carbon, and then you see nitrogen, phosphorous, we of course have a lot of calcium, calcium of course used in bones, but it's also used for things like muscle contractions. And I could keep on going down this list, and you will see these other elements in your study of biology, but the big picture is that even though biological systems can get fairly complex, they're made up of similar building blocks, and these elemental building blocks come from the environment in which these biological systems exist and evolved.