Proteins and Enzymes

ID #1622

Can you please explain why this is true: In a dipeptide, the bond that links the carboxyl group of the N-terminal amino acid to the amino group of the C-terminal amino acid is called a peptide bond. I thought that the carboxyl group is in the C-terminal and the amino group is in the N-terminal? Or do I have that backwards?


You're right that the C-terminus of an amino acid or protein is the end with the unoccupied carboxyl group, and the N-terminus is the end with the unoccupied amino group. But in a dipeptide, one of those amino acids is at the N-terminus of the peptide and the other is at the C-terminus. When these were joined, as with all protein synthesis, it was the amino group of the incoming amino acid that gets joined with the carboxyl group of the last link in the chain (or in this case, the only other one).

 

Basically, it's an issue of understanding that the individual amino acids have N- and C-termini, but so does the whole polypeptide.

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