C nomenclature in aminoacids

[mather]

hello!

biological aminoacids are named a-aminoacids, because their functional unit is in a-carbon

what is called a-carbon?

thanks!

 

[Borek]

α (Greek alpha), not a.

http://en.wikipedia.org/wiki/Alpha_and_beta_carbon

 

[mather]

> The alpha carbon in organic chemistry refers to the first carbon that attaches to a functional group (the carbon is attached at the first, or alpha, position).

1) the first starting from where?
2) in aminoacids, why isn't the C of the COOH, the first carbon, since that carbon holds an OH, which is a functional group?

 

[AGNuke]

1) Starting from functional group. In the example of ethyl alcohol, the carbon attached to -OH is alpha carbon.

2) The -COOH is collectively a carboxylic functional group. -OH is Hydroxyl group, different from Carboxylic.

C=O and C-O-H are attached to the same Carbon. So, the Carbon attached to this carbon is considered alpha carbon.

Also, read the protein section in the link given by Borek. Alpha Carbon is "backbone" carbon attached to Carbonyl (C=O) group.

 

[mather]

1) Starting from functional group.

which functional group exactly? is there a hierarchy of functional groups that we start first from?

Also, read the protein section in the link given by Borek. Alpha Carbon is "backbone" carbon attached to Carbonyl (C=O) group.

so only backbone carbons are considered?

 

[Borek]

which functional group exactly? is there a hierarchy of functional groups that we start first from?

Answered in the wikipedia article.

 

[mather]

ok, so exclusively in proteins and despite what happens in other molecules, we consider a-carbon, the carbon where the COOH binds to, just that

but why "Polypeptide chains are described by starting at the amino terminus (known as the N-terminus) and sequentially naming each residue until the carboxyl terminus (the C-terminus) is reached" ?