Message 1 of 7 (13617)
07-16-2002 3:23 AM
Protein folding finally gets its own thread! Let no-one ever again think of genes as simply lists of A, G, C and Ts!
Here is a great mainstream web site explaining protein folding and protein folds (we have talked a lot about this in various threads around here):
For example we see that estimates put only about 1 in 10,000 random sequences folding at all and of course these would be non-functional. So a new gene starting from random DNA (or drastically altering fold from an existing gene) has to fight this sort of barrier even before it can begin to be selected for. After chancing on to a foldable sequence it still has no function so it will drift away from the foldable sequence.
PS - for any protein newbies here, proteins are what genes code for and they make the world go around by doing all of the structural, catalytic, signalling, detecting, transport, motor and metabolic funcitons of the cell either directily or after making a non-protein chemical to do the job. They only do this job if they have (i) a foldable seqeunce, (ii) have an active or catalytic site and (iii) this biochemical function is useful in some cellular context.
On this web page you can find some beautiful schematics of protein folds (scroll to bottom):
Here is the web site where structural biologists deposit these 3D datasets determined by X-ray crystallography and NMR (predciton from seqeunces is an ongoing struggle but progress is being made):
although here is probably a better site where one can peruse all of the known folds via the "CATH" catalog:
Here is a rather impressive prtoein fold (click on image for a larger view, alpha-helices are magenta and beta-strands are yellow):
(The amazing thing is that just about every individual molecule with that sequence will fold to that exact shape so that it can do a very specific job.)
Here's another fold:
and one more:
And here's how the cell makes proteins from RNA copied from DNA on a gene:
The ribosome that reads the RNA and strings the amino-acids of the protein together (green in the previous link) is itself an association of about 50 proteins and RNA:
So sometimes, the ribosome unknown to itself, is making more of itself. Here is a rotating model of the 50S half:
Each of the colored bits is a folded ribosmal protein required to make the ribosome translate RNA into protein. The gray is structural RNA (not the RNA that is translated). Here is the other half of the ribosome complex:
[This message has been edited by Tranquility Base, 07-16-2002]
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