Talk:Amino acid

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Good article Amino acid has been listed as one of the Natural sciences good articles under the good article criteria. If you can improve it further, please do. If it no longer meets these criteria, you can delist it, or ask for a reassessment.
March 13, 2007 Good article nominee Listed
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[edit] GA-review

This was an easy promotion - great job. I really had no comments although I do see that this project is still evolving and being improved. I would suggest a peer review in a couple of months followed by an attempt for Featured article status.Peter Rehse 06:50, 14 March 2007 (UTC)

[edit] Dur I reverts lots.

Didn't see that Crazycomputers had already caught the vandalism when I reverted. Sorry. XD --AgentCDE 17:05, 22 March 2007 (UTC)

[edit] Proline

general formula NH2CHRCOOH

IANABC (I Am Not A BioChemist) but the formula doesn't fit for proline with its secondary amine ... should it be changed? Daen 03:07, 25 March 2007 (UTC)

No. Proline's amine group cyclizes on the alpha carbon, true, but the general formula still holds if you think of one of nitrogen's hydrogens plus the rest of the ring as the R-group. --Cless Alvein 08:00, 30 March 2007 (UTC)
That general formula is not valid for proline. You can think of the R group in various ways, but proline simply doesn't have the NH2 that appears in the "general" formula. I'll add this as a footnote, since this level of detail could detract from the conciseness of the introduction. --Itub 08:34, 30 March 2007 (UTC)

[edit] Other Amino Acids

The article seems to be focused on "Life's Building Blocks". But what about the other amino acids? How many amino acids have been discovered? Besides life, what else builds, delivers, or uses amino acids? WynnSmith 19:04, 16 April 2007 (UTC)

I can understand your first point, but what exactly do you expect to 'build' amino acids, or use them, besides life? They would be created by e.g. a lightning storm in the 'primordial soup' environment, but besides life, they certainly aren't going to be 'utilized' by anything else. Richard001 01:31, 22 July 2007 (UTC)
In fact, there are many, many amino acids beyond those encoded by DNA, most of which are generated by post-translational processing of the standard 20 but some that arise from more esoteric biosynthetic processes. And many other amino acids are synthetic that have been incorporated into proteins or used for various purposes related to engineered enzymes.

[edit] BCAA

The branched chain amino acid paragraph is a little unusual - the aliphatic/hydrocarbon side chains are often just categorized as aliphatic side chains (Leu, Val, Ile). I've almost always heard branched amino acids used to refer to the beta-branched amino acids, which include Ile, Thr, and Val. This is a useful category because the branching affects the geometry of the protein backbone immediately surrounding the amino acids, and thus the protein structure. I don't know the history of the page - is there a reason that the branched chain aliphatic category was given precedence? Reesei 19:30, 1 May 2007 (UTC)

[edit] Genetic code

Perhaps there should be a little mention that many codons code for the same amino acid, and its implication for mutations? This area seems fairly underdeveloped, in fact the genetic code is only mentioned a couple of times and not in any detail. Richard001 06:05, 29 July 2007 (UTC)

[edit] Tyrosine polar/non-polar

It seems there have been a few edits back and forth mentioning Tyrosine as non-polar or polar. As far as I am aware, Tyrosine is considered a polar amino acid because of the hydroxyl group. One may also check the much-cited Venn-diagram found at EMBL [1](which was a source for a figure I remember from an advanced-level protein engineering class I took a few years ago). Any comments? Antorjal 03:25, 2 August 2007 (UTC)

I'll have a look at Chrighton Proteins when I get into work tomorrow. However, if you look at the hydropathy index in the table, it is about as polar as proline, which is also labelled as "non-polar". Tim Vickers 03:35, 2 August 2007 (UTC)
With that I will agree with you 100%. Tyrosine was always one of the strange cases (along with good old tryptophan), where due to convention the amino acid was considered hydrophobic and polar. Go figure! In any case I'll go through "Fersht" tomorrow as well. :-) Have a nice night.Antorjal 03:41, 2 August 2007 (UTC)
It is my understanding that Tyrosine is part of the grouping - polar uncharged. Because it's side chain amino acid has a pKr of 10.46, it has the possibility to become polar/charged in rare but possible cases of physiological pH, whereas proline and tryptophan have negligible pKr values for their side change. —Preceding unsigned comment added by Niubrad (talk • contribs) 02:47, 28 February 2008 (UTC)

[edit] Biological importance-Tyrosine/Tryptophan

Why do all biological proteins contain Tyrosine and Tryptophan?? Any specific reason??

Not as far as I know, the chances of any string of amino acids not containing two of the twenty amino acids is pretty small, even if the sequence is just random. Collagen contains only a few Y/W residues and there might be some proteins with none, but I would expect them to be pretty rare. Tim Vickers 06:46, 5 August 2007 (UTC)
To add to Tim Vickers's excellent response, tyrosine is a lot more common that tryptophan, but even so, (depending on the species) more than 90% of proteins have at least one W.Antorjal 12:57, 5 August 2007 (UTC)

[edit] Essential

i have a health book that says there are nine essential and 11 nonessential amino acids Soyseñorsnibbles 23:00, 28 September 2007 (UTC)

This seems surprisingly ill-defined and controversial. I've added a range of references. Tim Vickers 02:39, 29 September 2007 (UTC)

[edit] Cysteine

Presentation College,There is one querry that i have . Cystein , as an amino acid ... is it Polar ? I have a text book by Richard Kent which argues thet it is Non Polar ... —Preceding unsigned comment added by 190.58.4.66 (talk) 04:40, 16 October 2007 (UTC)

It is non-polar when protonated but polar when ionised. Tim Vickers 18:03, 4 December 2007 (UTC)

[edit] Side chain polarity

I am going to have to strongly disagree with the assertion that the side chain of tyrosine is nonpolar. Although it can base stack and have hydrophobic interactions with its electrons above and below the plane of the aromatic ring, there is no conceivable way that you can tell me that it is nonpolar with the conspicuous hydrogen bonding phenolic oxygen —Preceding unsigned comment added by 68.242.170.102 (talk) 16:25, 27 November 2007 (UTC)

This is one on the boundary, it has both polar and nonpolar characteristics and does not easily fit into a black/white classification. Tim Vickers 18:04, 4 December 2007 (UTC)

[edit] Origins and evolution

This article could benefit from a section on the origins and evolution of amino acids. I'm thinking in particular of the Miller-Urey experiment and the question of handedness.[2] -- Beland (talk) 01:10, 4 January 2008 (UTC)