The Fine Art of Protein Folding

Art, whether it’s abstract or otherwise, always has a story. Protein folding is no different. Protein folding is something that happens in our bodies every day, every hour, and perhaps every minute, but it’s so complex that it takes a computer hours (or even days depending on what researchers are looking for) to figure it out.

So, it begins…

It all starts with DNA or Deoxyribonucleic acid and ends with a set of molecules that fold into a protein.

DNA is in the nucleus within each non-sex cell (somatic cell). Each nucleus of a somatic cell has the complete set of DNA for an animal or plant.

DNA is a polymer of nucleotides (the molecules that are the building-blocks for nucleic acids). Nucleotides found in DNA have a nitrogenous base (adenine, thymine, cytosine, or guanine, commonly notated as A, T, C, and G), a sugar group (deoxyribose), and a phosphate group. The nitrogenous bases are bound together by hydrogen bonds. They connect to the sugar-phosphate groups that make up the hand-rails of DNA. These bases are complementary, meaning that each one has a partner that it attaches to on the DNA strand. Adenine binds to thymine and cytosine binds to guanine.

An enzyme (a protein that speeds up biochemical reactions) called RNA polymerase unzips a section of DNA (this section is called a template strand) so that an mRNA or messenger ribonucleic acid can copy it (this is “transcription”). When mRNA copies the template strand from DNA, it substitutes thymine with uracil. The mRNA then leaves the nucleus to find a ribosome (a structure that serves as the site of protein synthesis) swimming around in the cytoplasm of the cell. Ribosomes have two subunits which come together after mRNA attaches to one of the subunits.

Another type of RNA in the cell, called transfer RNA or tRNA, attaches to an amino acid and connects to the ribosome with the mRNA inside. Depending on what the mRNA strand codes for, and whether the right tRNA has attached, a polypeptide chain will excrete from the ribosome (this is “translation”). The sequence of amino acids in the chain determine the protein (a typical protein has hundreds). If the chain formed correctly, it will fold up turning into a functional protein.

Amino acids have a carboxyl group, an amino acid group, a lone hydrogen, a carbon, and a side chain that determines the amino acid. There are twenty different amino acids that make up proteins and enzymes.

The mRNA code for amino acids. To code for one amino acid, it takes three nitrogenous bases on the mRNA strand (called a triplet code – each triplet code called a codon). For example, the triplet code for methionine is AUG (nitrogenous bases: adenine, uracil, and guanine) in mRNA. A tRNA molecule, with the methionine amino acid, fits into these correct sequence of nitrogenous bases. The attachment site of the tRNA that fits into the triplet code is called the anticodon.

The codon on the mRNA connects with the anticodon on the tRNA. When this is complete and it’s the right amino acid, the tRNA leave and the amino acid join to the other amino acids to create the polypeptide chain (the basic building block of proteins). The polypeptide chain always starts with the amino acid called methionine and ends with a stop amino acid (an amino acid that codes for the polypeptide chain to end). When the right amino acids are in place, the polypeptide chain detach from the ribosome and fold into a protein.

Proteins have several structures called primary, secondary, tertiary, and quaternary. The primary structure is the polypeptide chain. The secondary structure is when the polypeptide chain fold up into beta-pleated sheets, alpha helices, or random coils. The tertiary structure is a polypeptide chain that folded. A quaternary structure is when several polypeptide chains linked together to form a bigger protein.

This is a wonderful example of how complex and beautiful organisms are. What do you think?


Reference:
Krogh, David (2011). Biology: a Guide to the Natural World.California; Pearson, 2011. Print.
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