Question

7. a). Why should the core of most globular and membrane proteins consist almost entirely of α-helix and β-

sheets?

b). Name the structural and functional advantages of having proteins with a quaternary structure.

c). In a protein, what amino acids (polar or non-polar) would mostly be in the interior folds?

Give a reason for your answer.

d) On the surface of a folded protein, amino acids with what properties would be more predominant?

Give a reason for your answer.

Answer 1

a) Highly polar N-H and C=O moieties of the peptide backbone must be neutralized in the hydrophobic core of the protein. Therefore the globular and membrane proteins consist almost entirely of α-helix and β- sheets.

b) The Structural and functional advantages of quaternary structure are as following:

              i) The quaternary structure gives extra stability to the protein molecule.

              ii) This structure provides genetic economy and efficiency during coding.

              iii) This structure helps in Host-Guest interaction gor enzymatic activities.

              iv) The quternary structure promotes copperativity between the units as one unit influences the other.

c) The interior folds contain mostly amino acids with hydrophobic side chain like

• Alanine - Ala - A
• Isoleucine - Ile - I
• Leucine - Leu - L
• Phenylalanine - Phe - F
• Valine - Val - V
• Proline - Pro - P
• Glycine - Gly - G

d) The outer surface contain mostly amino acids with polar side chain like

• Glutamine - Gln - Q
  • Asparagine - Asn - N
  • Histidine - His - H
  • Serine - Ser - S
  • Threonine - Thr - T
  • Tyrosine - Tyr - Y
  • Cysteine - Cys - C
  • Methionine - Met - M
  • Tryptophan - Trp - W