Module 4, Lectures 7,8

Question 1

Describe peptide bonds?

Answer 1

Amino acids are bonded together via nucleophilic acyl substitution reactions of the amine group (the nucleophile) on one with the carboxylic acid group (the acid derivative) on the other to form peptides. The bond formed is an amide bond, but, in this context, it is called a
peptide bond.

Question 2

How are peptides illustrated?

Answer 2

By convention when we draw the peptide with the unreacted amine group (the Terminal) on the left and the unreacted carboxylic acid group (the C-terminal) on the right.

Question 3

Structure of peptides?

Answer 3

<75 amino acids
primary structure
secondary structure 
tertiary structure
Quaternary Structure

Question 4

What is peptide hydrolysis?

Answer 4

A peptide bond can be broken by hydrolysis. However it is difficult as it is an unreactive acid derivative and water is a poor nucleophile.

Question 5

What is peptide synthesis

Answer 5

Formation of peptide bonds. Must use protecting groups to temporarily stop groups being able to react – just
have the correct amine and carboxylic acid groups combining to form the peptide bond.

Question 6

What initiates hydrolysis of peptide bonds?

Answer 6

Free amino acids are required for many biological processes so a variety of enzymes called proteases are synthesised to enable the efficient hydrolysis of peptide bonds

Question 7

Chymotrypsin?

Answer 7

• breaks peptide bonds on the carboxyl side of ‘aromatic’ amino acids (ones whose side chain contains a benzene
  ring)
• Active site contains a “catalytic triad” of amino acids

Question 8

Carboxypeptidase

Answer 8

• breaks peptide bonds to remove the C-terminal amino acid

- Metalloenzyme – contains a Zn2+ ion which is key to the catalysis of the reaction