How Does DNA Code for Proteins to Form Complex Shapes Like Viruses?

[aychamo]

Ok, so how does DNA build things? Say, even something as simple as a virus. The virus inserts its DNA or RNA or whatever, and it's coded into proteins.

So how does the protein make a shape? Like in that T4 virus that looks like the lunar lander thing, how do the proteins assemble into the shape of the head? That complex, round shape? Or to make the legs, etc. I guess what I'm asking is how do proteins end up forming shapes?

 

[Monique]

Well, simply said DNA is translated into RNA, and RNA gets transcribed into a protein. There are several different ways to look at a protein:

primary-the sequence of amino acids
secondary-the structure of the string of amino acids, you can have an alpha-helix, beta-sheet, turns, loops
teriary-the overall 3d structure of the molecule (barrel for instance)
quaternairy-the 3d structure of protein complexes, how several molecules have an interaction with each other (like hemoglobin, which consists of four polypeptide chains bound by a heme group).

So how does it shape? Well, there are hydrophobic and hydrophilic amino acids. You can imagine that in a hydrophilic environment, hydrophobic molecules will tend to turn inward of a molecule. This is for instance what causes the formation of an alpha-helix. Things like hydrogen bonding stabilize the structure, but also covalent bonds like the disulfide bridge (under non-reducing conditions).

There are different ways that molecules can fold, and there is not one path that every molecule follows. Some molecules start folding from the middle, others from the end, some while being synthesized, others after it has been processed further. There is question also whether the disulfide bridges actually help in the folding process, or are a byproduct after folding has occurred.

There are also all kinds of chaperones that help in the folding process, these molecules are very interesting for crystalographers who want to make crystals of proteins to elucidate their structure by x-ray crystalography. It was shown if some molecule X was added to X proteins, it folded much quicker and efficiently.

So really the process is quite complicated, there are all kinds of internal safety controls in that cell that insure that a protein folds properly. I don't remember the exact number, but only a small portion of synthesized protein will actually end up as function, the rest is rapidly degraded (in some instances the system goes haywire, there is a mutation in Cystic Fibrosis for instance, where the protein is still functional but never ends up in its proper place, since the mutation causes a misfold and is thus rapidly degraded).