Question 1

Which of the following best describes the bond that links two amino acids together in a polypeptide chain?

Accepted Answer

A peptide bond between the amino group of one amino acid and the carboxyl group of another

Question 2

A mutation changes a nonpolar amino acid in the hydrophobic core of a protein to a charged amino acid. What is the most likely effect on the protein's structure?

Accepted Answer

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

Question 3

Which of the following statements about protein secondary structure is correct?

Accepted Answer

It includes alpha helices and beta sheets stabilized by hydrogen bonds between backbone atoms

Question 4

Which amino acid is most likely to form a disulfide bond within a protein?

Accepted Answer

Cysteine

Question 5

A researcher is studying an enzyme-catalyzed reaction. She finds that the reaction rate increases rapidly with substrate concentration, but then levels off even as more substrate is added. Which equation best describes this behavior?

Accepted Answer

$$v = \frac{V_{max}[S]}{K_m + [S]}$$

Question 6

Which of the following best explains why enzymes are highly specific for their substrates?

Accepted Answer

Enzymes have active sites whose shape and chemical environment are complementary to the substrate

Question 7

A protein is regulated by phosphorylation. Which of the following enzymes is responsible for removing the phosphate group?

Accepted Answer

Phosphatase

Question 8

Which of the following is a correct statement about GTP-binding proteins (GTPases)?

Accepted Answer

They are active when bound to GTP and can hydrolyze GTP to turn themselves off

Question 9

A patient with a neurodegenerative disease is found to have aggregates of misfolded proteins in their brain tissue. Which process is most likely failing in this scenario?

Accepted Answer

Protein quality control and degradation

Question 10

Which of the following best describes the role of ubiquitin in the cell?

Accepted Answer

It is a small protein that tags other proteins for degradation

Question 11

Which of the following interactions is NOT typically involved in stabilizing the tertiary structure of a protein?

Accepted Answer

Peptide bonds between amino acids

Question 12

A protein is found to have a quaternary structure. Which of the following must be true?

Accepted Answer

It is composed of more than one polypeptide chain

Question 13

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

Accepted Answer

Aspartic acid

Question 14

Which of the following best explains why enzymes lower the activation energy of a reaction?

Accepted Answer

They stabilize the transition state, making it easier to form

Question 15

A scientist is studying a protein that can bind to multiple partners with different affinities. Which property of protein interactions does this illustrate?

Accepted Answer

Affinity

Question 16

Which of the following is a correct statement about the self-assembly of viral capsids?

Accepted Answer

It occurs spontaneously due to the properties of the protein subunits

Question 17

A protein kinase is most likely to regulate its target protein by which of the following mechanisms?

Accepted Answer

Adding a phosphate group to a specific amino acid residue

Question 18

Which of the following best describes the 'induced fit' model of enzyme function?

Accepted Answer

The enzyme changes shape slightly to better fit the substrate upon binding

Question 19

Which of the following is a likely consequence if a protein fails to be ubiquitylated in a cell?

Accepted Answer

It may accumulate and potentially form toxic aggregates

Question 20

A protein is found to be active only when bound to GTP, and inactive when bound to GDP. Which type of protein is this most likely to be?

Accepted Answer

A GTPase

Proteins: Structure, Function, and Regulation (Molecular Biology of the Cell, Ch. 3)

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