I really do not plan on going overboard with this article because I can make this an hour long if I wanted to. Anyone that knows me, knows that I have a high fascination in protein synthesis and functionality. Because of these molecular machines, I indulged myself in the studies of the origin of life. Proteins are so complex and act as finite machines that help drive biological reactions and sustain life. They are important to homeostasis, cell replication, cell structure, and regulation. The fine details of proteins have always had a place in heart; it has opened up my curiosity and hunger for more knowledge of these molecules.
Mind Blowing Fact: Proteins account for more than 50% of cellular mass!
So What Is A Protein Exactly?
Enough about my fascination with these guys. Let me introduce you to what proteins are. Proteins are macromolecules that are essential to all of life. They are made up of units called amino acids. When these amino acids link together, they form polypeptides and eventually functional proteins. Amino acids are the building blocks for proteins, with 20 of them being essential to life and found in the human body.
Polypeptides are long chains of amino acids that are linked together by peptide bonds. The reaction involved in this linkage is called a dehydration or condensation reaction. A covalent bond is formed between the amino group(NH2) and the hydroxyl group(-OH) of amino acids. After multiple rounds of peptide bond formations, a polypeptide is formed.
These polypeptides can fold into certain configurations by side chain interactions between certain amino acids. For example, the sulfur(-SH) in the side chain of cysteine forms a disulfide bridge, allowing for the polypeptide to fold( as seen in the photo above). Other side chain interactions include electrostatic bonding and hydrogen bonds.
This Is Where It Gets Interesting
Now that we have the textbook stuff out of the way, we can talk about what happens when the larger structures are formed through peptide bond formations. In the photo are the different categorizations for proteins: primary, secondary, tertiary and quaternary structures. We will focus on the last two structures since they are what makes proteins the most fascinating molecules. The reason for this is in the 3D structure proteins make after rounds of folding. Some of the most interesting proteins are ones that are in the quaternary structures.
Some examples of extraordinary proteins are regulatory proteins, transport proteins and structural proteins. The first protein I would like to bring to the stage in the chaperon/transport protein. These are literally proteins that fold or unfold other proteins into their conformational shape. They are typically found in the endoplasmic reticulum and account for about 10% of the cellular mass. A non-native protein is added to the target protein thus forming the appropriate fold. These chaperon proteins resemble a barrel with a lid. Let's take this in guys, we have an actual machine that brings in a polypeptide and caps it, then releases a new protein. The superpowers of chaperon proteins do no stop here.
Chaperon proteins not only are responsible for creating the appropriate folds, but they also protect them from interacting with other proteins that may bind and interrupt the process. Think of these as shields for the protein it is working with at the time. The target protein gets undivided attention by the chaperon proteins and a massage at the spa to get its configuration in shape.
Our next contestant up is ubiquitin. This is a regulatory protein that tags faulty proteins within the cell. These proteins are so detailed that they require the fashion police(ubiquitin) to regulate whether proteins are folded correctly. In many videos by Dre's Tutoring, the main concept presented for proteins is that they must have the appropriate fold in order to be "fashionable"(or functional). After tagging any faulty proteins a proteasome comes in and degrades the protein into short polypeptides or amino acids that will be used in another process. Aren't these things smart?
The two proteins that I mention are only scratching the surface of cool proteins that are essential to life. Again, since I did not want to make this article a 100 hour read here are a list of cool proteins you may want to check out:
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