Amino acids and the genetic code

I know this isn't really an evolution question, but it concerns a related field (genetics), and since I was familiar with this site, and I thought that if I looked for a genetics forum I would find something too academic for me, I decided to post it here. If it's too off topic, feel free to ignore me.What I know:
Molecules in which 4 different groups of atoms are bonded to a central carbon atom are called "chiral" molecules. The different forms of a chiral molecule can have different properties, sometimes very different. Some amino acids are chiral molecules. Organisms use amino acids to make proteins.What I want to know:
When an amino acid is needed to make a protein, and there is more than one chiral form of the amino acid, can an organism use any of the different varieties or are some of them un-usable? Is there a different tRNA needed for each chiral form? Is this why several codons are often used to code for the same amino acid (ie. does UCU code for one variety of serine, while UCC codes for a different variety)?Okay, that's all. Thanks for your time.

not that that has stopped other topics from happening.I'm going to leave this one up to Percy to decide on. It's his forum, and he pays the bills.Adminnemooseus

I don't think we've ever had a popular vote to get a topic promoted. So this is a first. And I'm not waiting for anyone else to do it.Thread moved here from the Proposed New Topics forum.This message has been edited by AdminNosy, 09-23-2004 11:18 AM

Protein synthesis does not use Dextro froms of amino acids. All of the amino acids used in protein synthesis in living systems are levo, except for Glycine which isn't chiral.

According to what my wife told me last night, they all are, except for (she said) histidine. (She was trying to remember from the book so maybe she's wrong about that. Now that I look, the book says glycine.)In particular, these amino acids have exactly two chiral forms, I guess, which is sometimes referred to as "handedness" - living things, as far as I'm aware, use the left-handed amino acids, not the right-handed ones.So, which part of the genetic code specifies which stereoisomer? No part. Living things only use the left-handed amino acids. I don't believe that a right-handed amino acid would even connect to the tRNA, so it wouldn't even be used if it was present. No, this redundany in the Standard Code is simply a method to reduce harmfl mutations. It does not specify handedness or chirality.This message has been edited by crashfrog, 09-23-2004 11:31 AM

True, but even a protein made completely from l-amino acids can itself have chirality. And that protein is coded for by RNA.I'm eagerly awaiting creationists to come in and say that chirality means that abiogenesis can't occur

---

"Illuminant light,
illuminate me."

Oh I really hope they do! I did a physics essay on the possibility of the homochirality of DNA being caused by a slight handedness in the electroweak interaction. My conclusion was that it is entirely possible (based on the available papers I found), but that purely stochastic mechanisms offered a more likely solution. This would mean that the chirality of DNA in lifeforms was purely random. One chirality won out in the original self replicating molecules and simply became totally dominant.As an asside, I do remember one paper mentioning that some very basic lifeforms do utilise to opposite chirality to the rest of life. Unfortunately I don't remember which paper stated this so I can't verify it. Does anyone have any idea if i'm remembering correctly?

i had once thought that carbon (as in the "tetrahedron" geometry) might be responsible for chirality. I now think this a better idea.http://www.endeav.org/evolut/text/ohfrmab/ohfrmab.htmto further work on this idea I would like to pursue the possibility that Maxwell history and electrotonic cell have been mismathmatized.Attention Required! | CloudflareSpecifically I wonder if the electrotonic functions are not in the same FLOW as in the first link?This message has been edited by Brad McFall, 02-02-2005 17:55 AM