on a dna strand, how many copies of transcription information for a
particular protein are there?

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Request for Question Clarification by politicalguru-ga on 30 Oct 2003 04:18 PST

Dear JK Burton, 

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Clarification of Question by jkburton-ga on 30 Oct 2003 08:32 PST

how about this:  are there multiple copies of information for a
particular protein on a dna strand, or generally, do the proteins get
manufactured from one piece of information?

Hi jkburton,

I think Amalik did a good job (if in somewhat of a complex fashion) of
answering your question, but I'll take a stab at answering it in far
fewer words:

Every protein is coded by one sequence of DNA, which may not be all
together in one big chain on the chromosome.  Many protein sequences
are interrupted in the DNA molecule by what are called "introns" -
non-coding areas that get cut out of the messenger RNA strand that
codes for the actual protein. So, the answer to your question is,
"There is one copy of transcription information for any particular
protein on a DNA strand."

However, any given area of DNA could possibly code for more than one
protein.  There are, in theory, six different ways to "read" the DNA
sequence at any given areas of the chromosome.  This is because it
takes three DNA bases to code for one protein amino acid, so where you
start reading makes a big difference (think of the random sequence
ATCGGCTAATCGGCTA - if you start withe the first A you get ATC GGC TAA
etc., but if you start with the first T you get TCG GCT AAT etc.). 
Then you multiply those possibilities by two, since the molecule is a
double helix and has two coding strands...

It's estimated that the human chromosome contains 30,000 genes for
proteins, with additional information coded for the various molecules
that help with going from DNA to protein (ribosomes, tRNA, etc).

If you'd like a nice online overview of genetics and so on, I'd
suggest you "check out" some of the e-books at the National Library of
Medicine's Bookshelf:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=Books.  In
particular, Molecular Biology of the Cell is a standard textbook for
genetics.

You might also try the following sites (found by doing a Google search
for "basic genetics"):

Genetic Science Learning Center
http://gslc.genetics.utah.edu/units/basics/

The DNA Files
http://www.dnafiles.org/resources/res01.html

Oak Ridge National Laboratory: Genomics 101
http://www.ornl.gov/sci/techresources/Human_Genome/publicat/primer2001/1.shtml

Thanks for a fun question!

librariankt

exactly what i wanted, but a little late to actually help me!  

i was reading a biological computing paper and they were somehow using
multiple copies of protein info on the dna- which i thought was wrong-
but just needed to prove it to myself!

Your question needs to be reformulated.  Instead of speaking of copies
of transcription information, different genes have different
combinations of transcription factors and promoter sites.

A.  On a dna strand, how many copies of transcription information for
a
particular protein are there?  


Regulation of Eukaryotic Transcription I
http://oregonstate.edu/instruction/bb492/lectures/RegulationII.html

Most eukaryotic genes are regulated by multiple transcription-control
elements

Gene Regulation in Eukaryotes
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Promoter.html

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Promoter.html#The_basal_promoter
What turns on a particular gene in a particular cell is probably the
unique combination of promoter sites and the transcription factors
that are chosen


B.  Do the proteins get manufactured from one piece of information?
Note:  Heavily qualified answer.

In general, a eukaryotic (specific) protein gets manufactured from a
single (copy)
-- except for those that don't.
Both alleles in a heterozygote are equally expressed except in the
case of imprinting.
Also, environmental stress can lead to multiple genes for a single
protein. (note- we're now discussing bacteria).

Evolution - Gene Duplication
http://www.catalase.com/evogenedup.htm
One of the interesting experiments concerned depriving cells which
normally required glucose of glucose and providing them instead with
another sugar, xylose.
Cells from the chemostat were analysed and found to have gained
multiple copies of genes responsible for an early stage in glucose
metabolism. These additional genes occured as tandem repeats, a
section of DNA repeated a number of times over in sequence.
In this situation multiple copies were advantageous because the gene
responsible for glucose break down was not 100% specific for glucose.


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Search strategy

transcription control gene regulation
multiple copy gene regulation

Someone pointed out to me that in my heavily qualified response to B.
above, I answered only half of the question jkburton-ga asked in the
clarification of question.

"how about this:  are there multiple copies of information for a
particular protein on a dna strand, or generally, do the proteins get
manufactured from one piece of information?"

I answered the second half of this question, but not the first half.

"are there multiple copies of information for a particular protein on
a dna strand"

There is only one gene (copy) on a given dna strand but as we have
pairs of chromosomes there would be two copies for each gene within
each cell's nucleus.
For each DNA strand, a protein would be manufactured from that single
(copy) /gene.  But within the cell, proteins would be manufactured
from each copy on both homologous chromosome pairs, (except for those
that aren't).  Return to discussion of imprinting in previous answer.