Week 2

Question 1

parts of an amino acid

Answer 1

• alpha carbon to which all other atoms and groups are attached
• amino group (NH2)
• carboxyl group (COOH)
• R group - side chain

Question 2

how is a peptide bond formed?

Answer 2

• there is a reaction between the carboxyl group on one amino acid and the amino group on the other.
• the OH group on the carboxyl end of one amino acid reacts with the hydrogen atom on the amino group of the other to eliminate a molecule of water

Question 3

what two features are always present in polypeptides, even in short chains?

Answer 3

an amino end (N-terminus) and a carboxyl end (C-terminus)

Question 4

residues

Answer 4

what amino acids are referred to as once they have joined together into a polypeptide chain

Question 5

in an alpha helix, where does hydrogen bonding occur between residues?

Answer 5

• there is hydrogen bonding between an oxygen atom of the carbonyl group of residue ‘n’ and the hydrogen atom of the amide group of the residue ‘n+4’ on the same polypeptide chain
• this is repeated in a regular fashion (1 and 5, 2 and 6, 3 and 7)
• the peptide chain thus twists around on itself and forms a cylindrical structure (a stable alpha helix)

Question 6

are R-groups involved in the formation of alpha helices?

Answer 6

no