$$ \text{Protein} + \text{ATP} \rightarrow \text{Phosphorylated Protein} + \text{ADP} $$

Question 1

Which of the following best describes post-translational modification (PTM) in proteins?

Accepted Answer

A modification of proteins after translation that can affect their function, stability, or localization.

Question 2

Which of the following is NOT a common type of post-translational modification?

Accepted Answer

Transcription

Question 3

Phosphorylation typically involves the addition of a phosphate group to which amino acid residues?

Accepted Answer

Serine, threonine, and tyrosine

Question 4

Which enzyme is responsible for removing phosphate groups from proteins?

Accepted Answer

Phosphatase

Question 5

Ubiquitination is a post-translational modification that often targets proteins for which cellular process?

Accepted Answer

Proteasomal degradation

Question 6

Which of the following equations correctly represents the general reaction for phosphorylation of a protein?

Accepted Answer

$$ 	ext{Protein} + 	ext{ATP} ightarrow 	ext{Phosphorylated Protein} + 	ext{ADP} $$

Question 7

Which post-translational modification is most commonly associated with histone proteins and regulation of gene expression?

Accepted Answer

Acetylation

Question 8

A mutation in a gene encoding a ubiquitin ligase would most likely affect which cellular process?

Accepted Answer

Protein degradation

Question 9

Which of the following statements about post-translational modifications is TRUE?

Accepted Answer

They can regulate protein activity, localization, and stability.

Question 10

Which post-translational modification involves the addition of a small protein to lysine residues, often marking the protein for degradation?

Accepted Answer

Ubiquitination

Question 11

Which of the following is a direct consequence of acetylation of histone proteins?

Accepted Answer

Relaxation of chromatin structure and increased gene expression

Question 12

A patient presents with a genetic disorder that impairs protein phosphorylation. Which cellular process is most likely to be affected?

Accepted Answer

Signal transduction

Question 13

Which of the following is NOT a function of post-translational modifications?

Accepted Answer

Directly synthesizing proteins from DNA

Question 14

Which enzyme catalyzes the transfer of an acetyl group to a protein?

Accepted Answer

Acetyltransferase

Question 15

Which of the following post-translational modifications is most likely to affect the half-life of a protein in the cell?

Accepted Answer

Ubiquitination

Question 16

Which of the following is a multi-step process involving the sequential addition of ubiquitin molecules to a substrate protein?

Accepted Answer

Polyubiquitination

Question 17

Which post-translational modification is most likely to be involved in the activation of enzymes in response to extracellular signals?

Accepted Answer

Phosphorylation

Question 18

Which of the following best explains why post-translational modifications are important in medicine?

Accepted Answer

They can be targeted by drugs to treat diseases such as cancer and neurodegeneration.

Question 19

Which of the following is a real-life example of a disease caused by abnormal post-translational modification?

Accepted Answer

Cystic fibrosis due to defective protein folding and ubiquitination

Question 20

Which of the following best describes the role of peptidases in post-translational modification?

Accepted Answer

They cleave peptide bonds to activate or deactivate proteins.

Post-Translational Modification of Proteins

Study Guide - Practice Questions