Question 1

Which level of protein structure is directly responsible for the biological activity of a protein, and why can a single amino acid substitution at this level cause diseases such as sickle-cell anemia?

Accepted Answer

Primary structure, because the sequence of amino acids determines the protein's 3D conformation and function.

Question 2

Which of the following bonds in a polypeptide backbone allows for free rotation, contributing to the flexibility of protein structure?

Accepted Answer

Bond between the alpha-carbon and the amino nitrogen in residue N

Question 3

The planarity and resonance of the peptide bond restrict rotation around which bond in the polypeptide backbone?

Accepted Answer

The bond between the carbonyl carbon and the amino nitrogen (peptide bond)

Question 4

Which amino acid is most likely to disrupt an alpha-helix due to its cyclic structure and lack of an N-H group for hydrogen bonding?

Accepted Answer

Proline

Question 5

In an alpha-helix, how are the hydrogen bonds oriented relative to the helical axis, and what is the typical number of amino acids per turn?

Accepted Answer

Hydrogen bonds are parallel to the helical axis; there are 3.6 amino acids per turn.

Question 6

Which of the following statements best describes the difference between parallel and antiparallel beta-sheets?

Accepted Answer

Antiparallel beta-sheets have hydrogen bonds that are more linear and thus stronger than those in parallel beta-sheets.

Question 7

Which type of interaction is primarily responsible for the formation of a hydrophobic core in globular proteins?

Accepted Answer

Hydrophobic interactions between nonpolar side chains

Question 8

Collagen is a fibrous protein with a unique triple helix structure. Which repeating sequence is characteristic of collagen's polypeptide chains?

Accepted Answer

Gly-X-Pro or Gly-X-Hyp, where X is any amino acid

Question 9

Which of the following best explains why proteins fold spontaneously in aqueous environments?

Accepted Answer

The hydrophobic effect drives nonpolar side chains to the protein core, minimizing exposure to water.

Question 10

Which statement about protein denaturation is correct?

Accepted Answer

Denaturation disrupts secondary, tertiary, and quaternary structures, leading to loss of biological activity.

Question 11

Which of the following is a common method for disrupting disulfide bonds during protein denaturation?

Accepted Answer

Treatment with mercaptoethanol

Question 12

What is the role of chaperone proteins in the cell?

Accepted Answer

They assist in the correct and timely folding of other proteins.

Question 13

Which equation describes the fraction of protein bound to ligand ($$	heta) in a $$simple binding equilibrium?

Accepted Answer

$$	heta = \frac{[L]}{[L] + K_d}$$

Question 14

Myoglobin and hemoglobin both bind oxygen, but their binding curves differ. Which statement best explains this difference?

Accepted Answer

Hemoglobin exhibits a sigmoidal binding curve due to positive cooperativity, while myoglobin shows a hyperbolic curve.

Question 15

The Hill coefficient ($$n) is $$used to describe cooperativity in ligand binding. What does a Hill coefficient $$n \u003e 1$$ indicate?

Accepted Answer

Positive cooperativity: ligand binding increases the affinity for additional ligand binding.

Question 16

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

Accepted Answer

A decrease in pH (increase in H	extsuperscript{+}) reduces hemoglobin's affinity for O	extsubscript{2}, facilitating oxygen release in tissues.

Question 17

Which molecule acts as an allosteric effector by stabilizing the deoxy (T) state of hemoglobin, thus promoting oxygen release?

Accepted Answer

2,3-bisphosphoglycerate (BPG)

Question 18

A patient with a mutation that reduces the ability of hemoglobin to undergo the T to R state transition would most likely experience which physiological effect?

Accepted Answer

Reduced oxygen delivery to tissues due to decreased cooperativity and affinity change.

Question 19

Which of the following is a key difference between fibrous and globular proteins?

Accepted Answer

Fibrous proteins are generally insoluble in water and serve structural roles, while globular proteins are soluble and often have catalytic or transport functions.

Protein Structure and Function: A Study Guide Ch 4

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