A dazzling light reflects off the shiny veneer of abstract sculptures embracing hues of blue, pink, purple, and green. The mesmerized audience overflowing the museum is unaware that the artist of these structures is- well, themselves.
Protein-folding, with its pleated sheets and alpha helices, is crucial to understand, as an
incorrectly folded protein can commence the development of degenerative diseases like diabetes and Alzheimer's. To understand the kinetics and factors affecting protein-folding, we must first understand proteins themselves. Proteins are polymers, meaning they are conceived of building blocks called monomers. The monomers of proteins are amino acids, molecules with an amine group, a carboxyl group, and a carbon linked to an arbitrary "R" group.
There are 20 different
amino acids, each with the same chemical composition of an amine and carboxyl group. The
only difference between these 20 amino acids is the R-group, which can be a hydrocarbon group, neutral group, or acid/base group. Nine out of the 20 amino acids are "essential" because humans can't synthesize them. Instead, humans must digest them from outside sources such as fish, tofu, and beans. The nine "essential" amino acids vary in functionality, though most are involved in enabling cell interaction, are receptors on the surface of cells, assist in hormone and enzyme production, or aid in immune function.
Upon digestion, the proteins are broken down into their monomers (amino acids) for
reassembly. Why must they reassemble? Well, the body may require a specific protein as
opposed to the digested ones. Ribosomes, which are half ribosomal protein and ribosomal-RNA, receive a copy of a gene through a messenger-RNA. This process is known as translation, where the messenger-RNA sequence of a gene is translated into a 20-letter code of amino acids.
Translation groups nitrogenous bases (A, T, C, G) into threes; then, it translates this "codon" into an amino acid. For instance, the codon ATC translates into the amino acid Isoleucine. As a protein is synthesized, the intricate folding begins!
Proteins fold due to the interactions of the side chains of amino acids. Hydrophobic
(water-fearing) amino acid side chains, that are predominantly composed of carbon, cluster into the middle of a protein to create a "hydrophobic core". On the other hand, hydrophilic
(water-loving) side chains that often include nitrogen and oxygen reside on the exterior of the protein. Why? Water and the said side chains are polar, meaning they will attract one another due to the chemistry notion of "like attracts like". Terms such as "hydrophobic" and
"hydrophilic" apply to the case of protein-folding, as the environment of a cell is aqueous
Due to these interactions, proteins can fold in on themselves in various ways:
Primary protein structure- long chain of amino acids
Secondary Protein structure- pleated sheets and alpha helices due to hydrogen bonding of the protein backbone
Tertiary protein structure- 3-D folding pattern due to side-chain interactions
Quaternary Protein structure- multiple protein chains united through electrostatic interactions.
Protein folding, at the intersection of physics and biology, is