Rather than just start with “chromatin structure,” “heterochromatin,” “euchromatin,” and all the other “smallest parts” of biology, we think it’s best to begin Biochemistry with what is, conceptually, the most important idea: metabolism.
You are a human organism; so, let us understand what keeps this human body going:.
Entropy makes elements of us all. Entropy gradually and inevitably decomposes us all. Entropy favors our literal coming apart. The body, miraculously, has evolved to slow this process long enough for us to divide, procreate and, thereby, pass on our precious genes! We do this, interestingly, by breaking down compounds (carbohydrates, fats, and, as a last resort, proteins) which themselves have quite a bit of chemical energy stored in the form of bonds.
However, we don’t break these bonds all willy-nilly, releasing that precious chemical energy as uncaptured heat! No, my friends, that energy is transferred. It is transferred to an extremely useful chemical equivalent known as ATP.
Our cells know how to handle, store, and use, on demand, ATP. Putting the energy that was once in our food into the small molecule known as ATP allows us to “ship” and use that energy in nearly any enzymatic reaction (which cannot be said for molecules like glucose, fatty acids, and peptides). So, our body converts chemical energy in food to ATP, the common currency which all cells and most all reactions accept! (Kinda like VISA! hehe.)
ATP, in turn, drives all sorts of reactions in the body that entropy disfavors. What we mean by that is, while entropy wants things to come apart (since coming apart is actually energetically favorable), our bodies use ATP to drive reactions that keep things together.
So, ATP facilitates certain reactions which favor the “together-ness” of our bodies. Without ATP, we quite literally fall apart, decompose as it were.
So, let’s begin Biochemistry by talking about how we generate ATP. We’ve evolved to do so using three major categories: carbohydrates, fats and amino acids. (We can also breakdown nucleotides to form ATP but this is almost negligible when it comes to the overall ATP production of the body.)