Question 1

Which of the following statements best describes a zwitterion form of an amino acid at physiological pH?

Accepted Answer

The amino group is protonated and the carboxyl group is deprotonated.

Question 2

Which amino acid is achiral and why?

Accepted Answer

Glycine, because its R group is a hydrogen atom.

Question 3

A patient with methemoglobinemia has hemoglobin with iron in which oxidation state, and what is the consequence for oxygen delivery?

Accepted Answer

Fe$$^{3+}$$; decreased oxygen delivery to tissues

Question 4

Which of the following amino acids is most likely to disrupt an alpha helix in a protein structure?

Accepted Answer

Proline

Question 5

What is the isoelectric point ($$pI) of an $$amino acid with no ionizable R group, given $$pK_1 = 2.3$ and pK_2$ = 9.6$$?

Accepted Answer

$$pI = \frac{2.3 + 9.6}{2} = 5.95$$

Question 6

Which of the following best explains why hemoglobin exhibits a sigmoidal oxygen binding curve?

Accepted Answer

Hemoglobin undergoes cooperative binding, where binding of one O$$_2$$ increases the affinity for the next.

Question 7

Which of the following amino acids can be phosphorylated by protein kinases?

Accepted Answer

Serine, Threonine, and Tyrosine

Question 8

A protein is found to consist of two alpha and two beta subunits. Which level of protein structure does this describe?

Accepted Answer

Quaternary structure

Question 9

Which of the following is a correct statement about the peptide bond?

Accepted Answer

It is a covalent bond formed by a dehydration reaction between the carboxyl group of one amino acid and the amino group of another.

Question 10

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

Accepted Answer

Hemoglobin’s oxygen binding affinity decreases as pH decreases and CO$$_2$$ increases.

Question 11

Which of the following amino acids is essential in the human diet?

Accepted Answer

Leucine

Question 12

A mutation replaces a hydrophobic amino acid in the core of a protein with a charged amino acid. What is the most likely effect?

Accepted Answer

The protein may misfold or become unstable due to disruption of the hydrophobic core.

Question 13

Which of the following best describes the role of chaperone proteins?

Accepted Answer

They assist in the folding and assembly of other proteins without remaining part of the final structure.

Question 14

Which of the following amino acids contains a sulfur atom in its side chain?

Accepted Answer

Methionine

Question 15

Which of the following is a correct statement about the secondary structure of proteins?

Accepted Answer

It is stabilized primarily by hydrogen bonds between backbone atoms.

Question 16

Which of the following best explains why oxygen dissociates from hemoglobin in active muscle tissue?

Accepted Answer

Active muscle tissue has lower pH and higher CO$$_2$$, which decreases hemoglobin’s affinity for oxygen.

Question 17

Which of the following best describes the difference between Michaelis-Menten and Hill kinetics in oxygen binding proteins?

Accepted Answer

Michaelis-Menten kinetics applies to monomeric proteins like myoglobin, while Hill kinetics applies to multimeric proteins like hemoglobin.

Question 18

Which of the following is a function of protein domains?

Accepted Answer

They perform specific chemical or physical tasks within a protein, such as DNA binding or ligand binding.

Question 19

Which of the following best describes the effect of 2,3-bisphosphoglycerate (2,3-BPG) on hemoglobin?

Accepted Answer

It binds to deoxygenated hemoglobin and decreases its affinity for oxygen, promoting oxygen release.

Amino Acids and Protein Structure: Foundations for Biochemistry

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