Proteins

Question 1

Explain why maltase catalyses only this reaction?

Hydrolysis of maltose

Answer 1

Active site of enzyme has specific shape

Complementary to the substrate

Question 2

Describe the structure of proteins (5 marks)

Answer 2

1. Polymer of amino acids;
2. Joined by peptide bonds;
3. Formed by condensation;
4. Primary structure is order of amino acids;
5. Secondary structure is folding of polypeptide chain due to hydrogen
   bonding;
   Accept alpha helix / pleated sheet
6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic /disulfide bonds;
7. Quaternary structure is two or more polypeptide chains

Question 3

Name the type of reaction that joins amino acid monomers together?

Answer 3

Condensation reaction

Question 4

Compare and contrast the molecular structures of globular and fibrous proteins? (4 marks)

Answer 4

Both are chains of amino acids joined by peptide bonds
Both contain hydrogen bonds, holding it in a 3d shape
Globular proteins have hydrophilic groups on the outside and hydrophobic groups on the inside
Globular proteins have a tertiary or quaternary structure, whereas fibrous proteins have little or no tertiary structure
Globular proteins are folded into compact spheres, whereas fibrous proteins are long chains

Question 5

Give an example of a fibrous protein?

Answer 5

Cellulose

Question 6

Suggest how these two amino acids could be brought closer together to form part of the active site of this enzyme?

Answer 6

Formation of tertiary structure
Ionic + hydrogen + disulfide bonds
Between R groups

Question 7

How is a peptide bond formed? (2m)

Answer 7

A condensation reaction

Between the carboxyl group of one amino acid and the amine group of an adjacent amino acid