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What are Proteins and Where Do We Get Them? June 19, 2007

Posted by Hegemony in Science.
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I’ve said it before and I’ll say it again. We are protein based beings. Everything we do on a molecular level relies on a protein (note, an enzyme is a protein) in some way. I think a lot of people just don’t understand what that means. It all comes back to the Central Dogma. It’s a memorable term coined by Francis Crick (the co-discoverer of DNA along with James Watson) in 1958. It is basically the name given to the process by which genetic information is utilized. This is one of the most important concepts in biology. But it is not static as the term dogma would suggest, a fact often lamented by Francis Crick. We are finding new components of the central dogma even still. This is frankly, spectacular.

There are several main components of the central dogma. Firstly, DNA is a storage mechanism and is copied as cells divide. This is mediated by the enzyme DNA polymerase (in humans). When DNA is read by RNA polymerase (often triggered by an external stimulus) a strand of RNA is produced. RNA is much the same as DNA but in humans it is a single strand as opposed to the DNA’s double helix. This is called mRNA and the process by which it is made is called transcription. mRNA is exported to the cytosol from the nucleus and attaches to a ribosome. The ribosome reads the mRNA three bases at a time (this is called a codon). Each codon corresponds to a particular amino acid. Thus, the RNA is used to produce a chain of amino acids called a polypeptide. This then folds to attain its functional conformation (or shape) either by itself or with the help of chaperone proteins (a subject for a different article). This happens because the pattern of amino acids have different affinities to water, charges, and shapes. And that’s where you get your proteins.

But that’s not all there is to the central dogma. That’s what makes it interesting. In viruses we see an interesting variety of changes to the dogma. Many viruses store their genetic information as RNA instead of DNA. They may use RNA polymerases to replicate their genetic material. So here we see RNA producing RNA instead of DNA producing RNA as in humans. Some RNA viruses also use reverse transcription to change their RNA genome into DNA as a method of infecting cells.

Even now we are discovering new aspects of the central dogma that may apply to humans. New frontiers are opening up before us. Recent research indicates that some genes may be copied several times, and that the copy number may affect gene expression and thus, proteins. There is also the possibility that methylation plays a role in gene expression. This theory is called epigenetics, and basically says that changes in the physical structure of the DNA chain (caused by methylation) can alter expression. This structural change could even be inheritable… pretty cool. I hope this (long) post cleared up what proteins are and where we get them from.

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