[BiO BB] Re: Definition of a protein

Andrew Mitchell MitchellA at nu.ac.za
Fri Feb 22 01:44:29 EST 2002

Proteins are polypeptides. Peptides are short chains of amino acids.
Just how long can a peptide be before it should be called a protein? I'm
not going to stick my neck out a give a number, but one thing is clear:
2 amino acids does not a protein make.


Andrew Mitchell
Senior Lecturer, Molecular Phylogenetics
School of Molecular and Cellular Biosciences
University of Natal
Private Bag X01
Scottsville, 3209

Tel:  +27 (0)33 260 5815
Fax: +27 (0)33 260 5462


>>> bio_bulletin_board-request at bioinformatics.org 02/02/21 07:02:18 >>>
Message: 1
Date: Wed, 20 Feb 2002 13:15:45 -0500
From: hinaishadh at netscape.net
To: bio_bulletin_board at bioinformatics.org
Subject: [BiO BB] Definition of a protein
Reply-To: bio_bulletin_board at bioinformatics.org

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
>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)
>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
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