Genetics Basic Concepts
Proteins are large molecules that can perform many different jobs. They can facilitate chemical reactions (e.g., enzymes), provide structural support (e.g., cytoskeleton), transmit signals from the surface of the cell (e.g., membrane receptors), and much more. But where do they come from?
The genes in our DNA are similar to recipes used to make proteins. But since the recipes are coded using nitrogenous bases (ATCG), they must first be translated. Many proteins work together on this translation task. The strands of the DNA double helix must first give way so that the targeted gene may be accessed. Proteins then produce an identical copy of the targeted DNA sequence: a messenger RNA.
This copy of the recipe, now transcribed as an RNA messenger, is then sent outside the cell nucleus since proteins are made elsewhere in the cell. From there, ribosomes, small particles present in large number around the nucleus, will serve as chefs by reading the recipe to make the protein. Amino acids are the basic ingredients that go into the protein recipe and the ribosomes use the plan provided by the messenger RNA to put the amino acids in the right order and form a long chain. Amino acids are organic molecules that contain amine, a chemical compound derived from ammonia. Chemists know hundreds of amino acids, but only 20 of them form proteins. But proteins in this linear form are not yet ready. To function, it must fold up on itself origami style. This is when it changes from a single chain to a complex, three-dimensional structure.
RNA (ribonucleic acid) is almost identical to DNA (deoxyribonucleic acid). Its structure is similar on a chemical level, but less stable. While DNA has the shape of a twisted ladder formed by two complementary halves, RNA is most often composed of a single strand. It looks like a ladder that has been cut in half from top to bottom. As with DNA, RNA is made of four types of nitrogenous bases that line up in a very specific sequence. In DNA, these bases are adenine (A), thymine (T), cytosine (C) and guanine (G). But in RNA, thymine is replaced with uracil (U), which is also able to pair with adenine (A). But why do we not find uracil in DNA? It’s to make it easier to repair DNA when a mutation occurs. Cytosine is sometimes converted into uracil by mistake. If DNA was made up of uracil rather than thymine, it would be hard for the cell to know which uracil molecules are mistakes that need to be corrected. However, this problem does not apply to RNA because of its brief lifespan. More often than not, RNA molecules serve their purpose in just a few minutes before being recycled.