Question 1

Which of the following statements best explains why glycine is unique among the 20 standard amino acids?

Accepted Answer

Glycine is the only amino acid that is optically inactive due to its side chain being a hydrogen atom.

Question 2

At physiological pH (7.4), which amino acid side chain is most likely to act as a buffer due to its pKa being close to this value?

Accepted Answer

Histidine

Question 3

Which of the following best describes the primary structure of a protein?

Accepted Answer

The sequence of amino acids linked by peptide bonds.

Question 4

Which type of bond is formed between the carboxyl group of one amino acid and the amino group of another during protein synthesis?

Accepted Answer

Peptide bond

Question 5

Why is the trans conformation of the peptide bond generally favored over the cis conformation?

Accepted Answer

The trans conformation minimizes steric clashes between side chains.

Question 6

Which amino acid is most likely to introduce a kink in an alpha helix, disrupting its regular structure?

Accepted Answer

Proline

Question 7

A protein is exposed to 8M urea. What is the most likely effect on the protein's structure?

Accepted Answer

Urea will disrupt hydrogen bonds, leading to denaturation of secondary and tertiary structures.

Question 8

Which of the following interactions is most important for stabilizing the hydrophobic core of a globular protein?

Accepted Answer

Hydrophobic interactions and van der Waals forces

Question 9

Which amino acid can form a covalent disulfide bond, and why is this important for protein structure?

Accepted Answer

Cysteine; it forms disulfide bridges that stabilize tertiary and quaternary structures.

Question 10

A mutation replaces a glutamate residue with lysine in the interior of a protein. What is the most likely effect?

Accepted Answer

The protein may misfold due to disruption of ionic interactions and introduction of a positive charge.

Question 11

Which equation describes the relationship between pH, pKa, and the ratio of deprotonated to protonated forms of an amino acid side chain?

Accepted Answer

$$pH = pK_a + \log \frac{[A^-]}{[HA]}$$

Question 12

Which of the following best describes the quaternary structure of a protein?

Accepted Answer

The arrangement and interaction of multiple polypeptide subunits.

Question 13

Which of the following is a consequence of denaturation of a globular protein?

Accepted Answer

The protein loses its biological activity due to loss of its native conformation.

Question 14

Which of the following amino acids is essential and must be supplied in the diet?

Accepted Answer

Lysine

Question 15

Which of the following best explains why van der Waals and hydrogen bonding interactions are more important than covalent disulfide bonds in stabilizing the tertiary structure of most proteins?

Accepted Answer

There are more opportunities for van der Waals and hydrogen bonding interactions due to the large number of amino acids and the aqueous environment.

Question 16

A protein is found to have a high melting temperature ($$T_m) $$that decreases significantly when its disulfide bonds are reduced. What does this indicate about the role of disulfide bonds?

Accepted Answer

Disulfide bonds greatly increase the thermal stability of the protein.

Question 17

Which of the following best describes the hydrophobic effect in protein folding?

Accepted Answer

Hydrophobic side chains cluster in the protein interior, releasing ordered water molecules and stabilizing the folded state.

Question 18

Which of the following is a correct statement about the directionality of protein synthesis?

Accepted Answer

Proteins are synthesized from the amino terminus to the carboxyl terminus.

Question 19

Which of the following amino acids is most likely to be found at the active site of an enzyme due to its ability to act as both a proton donor and acceptor at physiological pH?

Accepted Answer

Histidine

Protein Structure and Function: Comprehensive Study Notes

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