Question

THIS IS A VERY VITAL QUESTION FOR ME..IS IT POSSIBLE TO HAVE TWO POLYPEPTIDES FROM ONE GENE CODE FOR A FORMATION OF A PROTEIN. IF THIS IS PERMITABLE, IT WOULD BE QUERY BECAUSE THERE IS NO SUCH THING AS TWO POLYPEPTIDES SINCE POLY IS A CONTINUOUS COUNTING ABOVE ONE...POLY COULD BE 200 PEPTIDES..SO HOW NUMBER OF PEPTIDES MAKE A POLYPEPTIDE IF TWO POLYPEPTIDES MAKE A SINGLE PROTEIN LIKE HEMOGLOBLIN.

Answer 1

could you rephrase the question, im not sure i follow. hemoglobin is made of 4 subunits, 2 alpha and 2 beta...

Answer 2

OK...NO PROBLEM..WHAT I AM ACTUALY TRYING TO CONVEY IS THAT IS IT POSSIBLE TO HAVE TWO POLYPEPTIDES FROM ONE GENE CODE FOR A FORMATION OF A PROTEIN...I MENTIONED HEMOGLOBIN AS AN EXAMPLE

Answer 3

First off, no more caps.

The different subunits of hemoglobin are encoded by different genes, not the same gene. Polypeptides generated from different genes can each form the subunits of some other enzyme, as the alpha and beta hemoglobin peptides do.

But a singe gene CAN code for multiple polypeptides. In most eukaryotes genes are subdivided into introns and exons. (see here http://en.wikipedia.org/wiki/Exon) Introns are chunks of DNA that get cut out of RNA before transalation. The exons are then glued back together. Different exons can be glued together to for the mRNA.

For example pretend this string is a piece of RNA freshly transcribed, letters indicate exons and '-'s indicate introns:
A---B---C---D

so the exons are cut out and we are left with an mRNA that looks like:
ABCD

but sometimes pieces will be left out, so we could end up with any of these as well:
ACD
AD
ABD
ABC

each oen would make a slightly different polypeptide when translated.

Answer 4

so what you are saying is that the same complementary strand of a gene can produce more than one different proteins depending on the way the exons are arranged on the mrna? you made a slight mistake, introns are cut off not exons and "AD" wont be able to correspond to any amino acid since its a base diplet.

Answer 5

ABCD above represent entire chunks of dna (since BC and D aren't even nucleotides) so imagine that each one is several hundred bases long. I just shortened them for the illustration. But yes you have the general idea.

Answer 6

thanks alot but is it really safe to refer exons as chunks of DNA? why not chunks on RNA since the DNA chunk has already been transcribed into RNA. or does it really matter

Answer 7

doesn't matter, the exons may be transcribed, but they are just going to get cut out broken down before leaving the nucleus