So far during the semester, we’ve discussed scientific structures by starting with the smaller parts and working up to the larger compositions. As we learned, protons, neutrons and electrons compose atoms. Each atom is distinguished by a different number of each of its components. This past week, we learned how amino acids, of which there are but 20, are the monomers or individual building blocks of proteins. We looked one step further back than just the amino acid itself. Amino acids are composed of an alpha carbon, an amino group (NH3+), an acidic carboxylate (COO-), a hydrogen atom (H) and the variable group (symbolized by “R”) that differentiates each of the 20 amino acids from one another. It is that variable side chain element that then names the amino acid.
Further, amino acids bond together by carboxyl and amino groups forming a peptide bond in a reaction that also creates water as a byproduct. Peptide bonded amino acids are then called amino acid residues because they have somewhat altered their structure from that of a single amino acid. So, amino acids are then monomers themselves of peptides and polypeptides and ultimately proteins when the chains are long enough.
Proteins appear to be irregularly shaped which helps them serve their wide array of jobs within organisms. They are an integral part in the functioning of a human and animal body. Proteins fold in on themselves encompassing a hydrophobic core with a hydrophilic outer surface. But, before they can form their hydrophobic core, the proteins must first fold. They fold into either α helices or β sheets depending on the requirements of the hydrogen bonds. An α helix is a helical structure enforced by hydrogen bonds between the C=O and the NH group of another amino acid residue 4 spaces ahead of it in the chain. This pattern causes the spiral helical shape. A β sheet on the other hand is formed by two or more β strands of proteins, which are formed by the interaction between two different amino acid residues. β sheets are flat and line up together, often in sets of 4 with two parallel strands in the middle surrounded by two additional strands in other directions on the outside.
The complexity of proteins that we learned about this past week has helped me understand why when a prion causes a different folding, it has such dire consequences.