Part 8 – Protein Manufacturing and Delivery
All the body processes we have looked at so far require the presence of a long list of proteins. In fact, the operation of the human body actually depends on 87,000+ different kinds of proteins, every one of which has to be built by the human body itself!
Our body's DNA carries the encoding for this extensive list of proteins. The machinery to assemble these proteins is found in the ribosome organelle of the cell. To see part of what is required to build a ribosome, check out this article in the journal Microbial Cell, https://microbialcell.com/researcharticles/when-a-ribosomal-protein-grows-up-the-ribosome-assembly-path-of-rps3/.
Within the ribosomes, catalysts work together with mRNA carrying the instructions to assemble proteins. This article by Nature Education provides a summary of how a protein is assembled in a ribosome: https://www.nature.com/scitable/topicpage/ribosomes-transcription-and-translation-14120660/. After this assembly process, some proteins are also acted upon by post-translational modification to change into their final state.
Once in their final state, each protein must then be transported either to a different part of the cell or through the cell membrane to be used outside the cell. Dozens of other proteins and enzymes are required to move the newly assembled protein. Some of these compounds open membranes; some initiate or deactivate reactions; some act on the newly made proteins to haul them, bend them to fit, or restraighten them. Today we have observed that if just one of the dozens of protein and enzyme transporters is lacking, the result can be fatal to the creature.
Assembled proteins are tagged with a molecular address label which causes the protein to follow a specific chemical delivery path based upon that address. This article from the Khan Academy (https://www.khanacademy.org/science/biology/gene-expression-central-dogma/translation-polypeptides/a/protein-targeting-and-traffic) details these different address labels and destinations. This article from the National Library of Medicine explains how proteins are moved through the ribosomes and through other organelles like the endoplasmic reticulum and Golgi apparatus: https://www.ncbi.nlm.nih.gov/books/NBK9889/.
In order for proteins to be utilized throughout the body, they must be tagged with the needed molecular substances determining a delivery sequence, or else they will not be delivered to the right organelle or secreted from the membrane as needed. Then, as we have seen previously, once the protein arrives in the organelle, organ, or system where it is needed, it must simultaneously be molecularly regulated to act at the right time in a sequence of reactions, to not react too much, and to not build up waste product that damages the organism.
Therefore, when we consider the likelihood that evolution generated a new protein, we must remember that far more is required than just the encoding in the DNA of the right sequence of amino acids. The introduction of a new protein in an organism requires the simultaneous appearance or availability of a molecular address label for delivery, a maintenance crew for transport, enzymes for activation and regulation, and a by-product waste management system. This reduces the probability of the generation of a new stable, functional, and system compatible protein.
Next in Part 9, we will take a look at another part of our body's delivery system.