[BiO BB] Definition of a protein

[hinaishadh at netscape.net]

Hi Kiran,
I am sure I will get a lot of flake for this BUT
Amino acids are building blocks of protein.  In other words proteins are polymers of amino acids.  How many? By definition 2 or more should do.

That said, keep in mind that earlier biochemical scientists did not know the nature of the molecule thay were working on.  So, the names like toxins, or even "active principle" in the ddays of Pasteur and Robert Koch (1870s!).  To further complicate matters you have glycoproteins that are mainly proteins with sugar side chains, and peptidoglycans that have small peptide backbone but really long, branched sugars chains (generally constituting 90% of the mol. wt. of the whole molecule).

LOts of work was done using precipitation as one way to isolate large biological molecules. So the growth factors and small peptides that were soluble by such criteria were not called proteins but peptides or peptide hormones etc.

Hope this helps

Naishadh Desai
Perlegen Sciences
Mountain View, CA 94043


>
>Message: 3
>Date: Wed, 20 Feb 2002 02:48:00 -0800 (PST)
>From: Ayyagari Kiran <kiran_ayyagari at yahoo.com>
>To: bio_bulletin_board at bioinformatics.org
>Subject: [BiO BB] what is the minimum length of protein? and why differentiate protein & peptides
>Reply-To: bio_bulletin_board at bioinformatics.org
>
>hi,
>1)what is the minimu length of  A protein ?
>(please mention the minimal possible length of
>protein, its minimal mol wt(in kDa) and also types of
>proteins by example.
>
>2) is it that a biomolecule can be called as a protein
>based on its structural organization (like if domains
>are present)
>or 
>is it that a biomolecule can be called as protein
>based on Functional implications??like example can be
>toxin of 55 amino acids causes raise in antibodies
>production. why is it not called a protein and why it
>is called a peptide toxin despite having amino acids.
>  
>thanks in advance
>
>A.S.Kiran
>
>
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