MadSci Network: Genetics
Query:

Re: is there a relationship between the size of a genome & protein created?

Date: Thu Sep 20 07:32:05 2007
Posted By: Mark Silby, Post-doc/Fellow, Molecular Biology and Microbiology, Tufts University School of Medicine
Area of science: Genetics
ID: 1189963307.Ge
Message:

Hi,
Good question! In the case of bacteria like E. coli, most people would say
that on average, one gene (which makes one protein) is about 1000 base
pairs long. It is also pretty well accepted that bacteria don't have a lot
of 'junk' DNA - the DNA found between genes for which no function is known
(note that this is probably not 'junk', it's likely to be important for
things we don't know about yet!). Given the average gene size, and the fact
that almost all of a bacterial genome consists of genes, one can easily
estimate the total number of proteins that could be made. So in this sense,
one could say there is a kind of rule dictating how many proteins should be
made from a genome of a given size.

There are other things going on in eukaryotes that make the picture
complicated. They have introns in their genes, meaning that the length of a
given gene is not necessarily reflective of the size of the protein it can
make. In addition, the eukaryotes have a lot of DNA between genes, which
doesn't code for proteins. We don't really know what most of this does
(this is the so-called 'junk' DNA - but I repeat, it's probably not junk!).
In fact, in humans there is less DNA in genes than there is between genes.
So the rule doesn't hold true in these creatures.

There is more than this, I suggest getting into the library and looking at
some of the newer genetics and genomics text books.


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