rorosingsong

Hi, I'm a little confused about the term "naturally occurring amino acid". Does this refer to the chirality of the amino acid at all? Some sources say that L-isomers are the "naturally occurring" amino acids, but others seem to suggest that this is a misconception. I've been given the structure of GABA (gamma aminobutyric acid) and asked if it is considered a naturally occuring amino acid. I know that it's synthesized from glutamate, has no chiral carbon and is not a protein forming amino acid... does that mean its not naturally occurring? Cheers, rorosingsong

Hi Mississipichem, thanks for your prompt reply! Um, I'm just a beginner so stop me if I'm wrong, but I'm guessing that the acetyl group will be elctron-withdrawing (due to the electronegativity of the carbonyl group), thus making the amine N of glutamine more likely to give up its proton...? This would make the glutamine more acidic and thus lower the pI....? Wait, amines are more basic than amides right?

Hi, I've just started studying molecular biology this semester and I'm a little stumped on a homework problem - would really appreciate some insight. I have a hypothetical hexapeptide with N-terminal Glutamine and C-terminal Arginine. The question is "If the N-terminal was acetylated how would this affect pI?" I know acetylation is the addition of an acetyl group (C2H3O), and that glutamine is a polar amino acid -- however it's uncharged at pH 7 and I can't see how the addition of an acetyl group would affect the charge of the molecule or the pI in anyway. We haven't covered acetylation in any of our lectures, so I'm really not sure about this at all. Please help! Thanks in advance, rorosingsong.