Q: A mutation replaces a glycine residue with proline in the middle of an $b1$-helix. What is the most likely effect on the protein's secondary structure?

The $b1$-helix will be disrupted because proline introduces a kink.

Q: Which of the following best describes the entropy change ($9S$) when hydrophobic amino acid residues are buried inside a protein during folding?

$9S$ of the protein decreases, $9S$ of water increases

Question 1

Which of the following best explains why nonpolar amino acid side chains are typically found in the interior of globular proteins in aqueous environments?

Accepted Answer

They are hydrophobic and their burial increases the entropy of surrounding water molecules.

Question 2

A researcher is studying a protein that contains several disulfide bonds. Which amino acid is directly involved in the formation of these bonds, and what type of reaction forms them?

Accepted Answer

Cysteine; oxidation

Question 3

At physiological pH ($pH = 7.4$), what is the net charge of the amino acid glutamic acid?

Accepted Answer

$-1$

Question 4

Which of the following statements about peptide bond formation is correct?

Accepted Answer

It is a condensation reaction that releases a molecule of water.

Question 5

A solution contains a mixture of glycine and lysine. The $pK_a$ values for glycine are $pK_{a,1} = 2.3$ and $pK_{a,2} = 9.6$. The $pK_a$ values for lysine are $pK_{a,1} = 2.2$, $pK_{a,2} = 9.0$, and $pK_{a,3} = 10.5$ (side chain). At $pH = 7.0$, which statement is true?

Accepted Answer

Glycine is a zwitterion and lysine has a net positive charge.

Question 6

Which level of protein structure is most directly determined by the sequence of nucleotides in a gene?

Accepted Answer

Primary structure

Question 7

A protein is exposed to a solution of 8 M urea. Which of the following is most likely to occur?

Accepted Answer

The protein will denature, losing its tertiary and quaternary structure.

Question 8

Which of the following amino acids contains a side chain that can be ionized at physiological pH?

Accepted Answer

Histidine

Question 9

A mutation replaces a glycine residue with proline in the middle of an $b1$-helix. What is the most likely effect on the protein's secondary structure?

Accepted Answer

The $b1$-helix will be disrupted because proline introduces a kink.

Question 10

Which of the following best describes the entropy change ($9S$) when hydrophobic amino acid residues are buried inside a protein during folding?

Accepted Answer

$9S$ of the protein decreases, $9S$ of water increases

Question 11

Which of the following is a function of quaternary protein structure?

Accepted Answer

Allowing cooperative binding and allosteric regulation

Question 12

A protein is found to have a prosthetic group containing iron. This protein is most likely classified as a:

Accepted Answer

Metalloprotein

Question 13

Which of the following amino acids is most likely to be found at the surface of a soluble, cytosolic protein?

Accepted Answer

Aspartate

Question 14

The isoelectric point ($pI$) of an amino acid with a non-ionizable side chain can be calculated as:

Accepted Answer

$pI = \frac{pK_{a,1} + pK_{a,2}}{2}$

Question 15

Which of the following best describes the effect of heating a protein to $100^{\circ}C$?

Accepted Answer

It disrupts hydrophobic interactions, leading to denaturation.

Question 16

A scientist wants to separate a mixture of proteins based on their isoelectric points. Which technique would be most appropriate?

Accepted Answer

Isoelectric focusing

Question 17

Which of the following amino acids is most likely to be found in high concentration in collagen, a protein with a triple helix structure?

Accepted Answer

Glycine

Question 18

A protein is found to consist of two identical polypeptide chains. Which level of structure is directly responsible for the arrangement of these chains?

Accepted Answer

Quaternary structure

Question 19

Which of the following amino acids has a side chain that contains a chiral center?

Accepted Answer

Threonine

Question 20

During protein synthesis, which functional group of one amino acid reacts with which functional group of another to form a peptide bond?

Accepted Answer

The amino group of one and the carboxyl group of another

Kaplan ch 1

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