Question 1

Which of the following statements best explains why the peptide bond in proteins is planar and rigid?

Accepted Answer

The peptide bond has partial double bond character due to resonance between the carbonyl oxygen and the amide nitrogen.

Question 2

A solution contains a peptide with the sequence Ala-Glu-Lys. Given the following pKa values: N-terminus = 9.0, C-terminus = 2.0, Glu side chain = 4.1, Lys side chain = 10.5. What is the isoelectric point ($$pI) of $$this peptide?

Accepted Answer

$$pI = \frac{4.1 + 10.5}{2} = 7.3$$

Question 3

Which of the following best describes the role of 2,3-bisphosphoglycerate (2,3-BPG) in hemoglobin function?

Accepted Answer

2,3-BPG binds to the T form of hemoglobin, stabilizing it and promoting oxygen release in tissues.

Question 4

A protein is purified using ion exchange chromatography. The protein has a net negative charge at pH 7. Which type of resin and elution condition would be most effective for its purification?

Accepted Answer

Anion exchange resin; elute with increasing salt concentration.

Question 5

Which of the following amino acids is most likely to be found in the turn region of a protein's secondary structure?

Accepted Answer

Proline

Question 6

A researcher uses SDS-PAGE to analyze a protein sample. What information does this technique primarily provide?

Accepted Answer

The protein's molecular weight

Question 7

Which of the following best describes the Bohr effect in hemoglobin?

Accepted Answer

A decrease in pH decreases hemoglobin's affinity for oxygen, promoting oxygen release in tissues.

Question 8

Which of the following statements about the Edman degradation is correct?

Accepted Answer

It uses phenylisothiocyanate (PITC) to label the N-terminal amino acid, which is then cleaved and identified.

Question 9

Given a peptide with the sequence Lys-Gly-Phe-Arg, which enzyme would cleave this peptide into two fragments, and at which position?

Accepted Answer

Chymotrypsin; after Phe

Question 10

A solution contains 0.1 M acetic acid ($$pK_a = 4.76) $$and 0.1 M sodium acetate. What is the pH of the solution according to the Henderson-Hasselbalch equation?

Accepted Answer

$$pH = 4.76 + \log\left(\frac{0.1}{0.1}\right) = 4.76$$

Question 11

Which of the following best explains why silk is strong and flexible?

Accepted Answer

It is composed of antiparallel $$\beta-$$sheets stabilized by extensive hydrogen bonding.

Question 12

Which of the following statements about the quaternary structure of hemoglobin is correct?

Accepted Answer

Hemoglobin consists of four subunits: two $$\alpha$$ and two $$\beta$$ chains.

Question 13

Which of the following amino acids is most likely to be found in the interior of a globular protein?

Accepted Answer

Leucine

Question 14

A protein sample is treated with 2-mercaptoethanol and iodoacetate before sequencing. What is the purpose of this treatment?

Accepted Answer

To reduce disulfide bonds and prevent their reformation by blocking sulfhydryl groups.

Question 15

Which of the following best describes the Hill coefficient in the context of hemoglobin's oxygen binding?

Accepted Answer

It quantifies the degree of cooperativity in oxygen binding.

Question 16

Which of the following statements about the L and D isomers of amino acids is correct?

Accepted Answer

L-amino acids are the predominant form found in proteins in living organisms.

Question 17

Which of the following best explains why collagen has high tensile strength?

Accepted Answer

It is composed of triple helical structures with a high content of glycine and proline.

Question 18

A protein is found to require a heme group for its function. The heme group is best described as:

Accepted Answer

A cofactor

Question 19

Which of the following best describes the effect of increasing temperature on the oxygen binding curve of hemoglobin?

Accepted Answer

The curve shifts to the right, indicating decreased oxygen affinity.

Amino Acids, Proteins, and Hemoglobin: Structure, Properties, and Function

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