Structure and Properties of Peptides – Section 1

26. Hemoglobin has a quaternary structure and is made up of

A. six polypeptide chains, two α-chains and four β-chains
B. two polypeptide chains, one α-chains and one β-chains
C. four polypeptide chains, two α-chains and two β-chains
D. five polypeptide chains, two α-chains and three β-chains

Correct Answer: C. four polypeptide chains, two α-chains and two β-chains

27. When pO2= Kd of myoglobin, the fractional saturation (YO2 ) is about

A. 0.1
B. 0.5
C. 0.9
D. 1.7

Correct Answer: B. 0.5

28. Peptides in the fully extended chain conformation

A. have Y = F = 180°
B. do not occur in nature
C. also have a cis geometry in their peptide bonds
D. are equivalent to the (3-sheet structure

Correct Answer: A. have Y = F = 180°

29. The oxygen in hemoglobin and myoglobin is bound to

A. the iron atom in the heme group
B. the nitrogen atoms on the heme
C. histidine residues in the protein
D. lysine residues in the protein

Correct Answer: A. the iron atom in the heme group

30. Which of the three subunits of the G proteins binds GDP and GTP?

A. Alpha
B. Beta
C. Gamma
D. Delta

Correct Answer: A. Alpha

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