$$\text{Asn}-\text{Any AA}-\text{Ser or Thr}$$

Question 1

Which of the following statements best describes the role of post-translational modifications (PTMs) in proteome complexity?

Accepted Answer

PTMs allow a single gene to produce multiple protein variants by modifying proteins after translation.

Question 2

Which amino acid sequence is required for N-linked glycosylation in proteins?

Accepted Answer

$$	ext{Asn}-	ext{Any AA}-	ext{Ser or Thr}$$

Question 3

Which enzyme is responsible for catalyzing the addition of a phosphate group to a protein during phosphorylation?

Accepted Answer

Kinase

Question 4

What is the primary function of ubiquitination in cells?

Accepted Answer

Targeting proteins for degradation via the proteasome pathway

Question 5

Which of the following post-translational modifications is most frequently reported on lysine residues and is essential for chromatin stability?

Accepted Answer

Acetylation

Question 6

A defect in glycosylation can lead to which of the following diseases?

Accepted Answer

Alzheimer’s disease

Question 7

Which of the following is TRUE regarding O-linked glycosylation?

Accepted Answer

It involves the attachment of N-acetylgalactosamine to serine or threonine residues.

Question 8

Which post-translational modification is involved in the regulation of gene expression by controlling chromatin structure?

Accepted Answer

Methylation

Question 9

During lysosomal enzyme sorting, which glycosylation motif is attached to proteins in the Golgi to direct them to the lysosome?

Accepted Answer

Mannose-6-phosphate

Question 10

Which of the following best explains why phosphorylation is a reversible modification?

Accepted Answer

Phosphorylation can be reversed by phosphatases, which hydrolyze the phosphate group.

Question 11

Which of the following is a consequence of phosphorylation on serine, threonine, or tyrosine residues?

Accepted Answer

It adds a strong negative charge and increases bulk.

Question 12

Which of the following is NOT a function of glycosylation?

Accepted Answer

Directing proteins for degradation via the proteasome

Question 13

Which enzyme is responsible for removing an acetyl group from lysine side chains?

Accepted Answer

Histone deacetylase (HDAC)

Question 14

Which of the following best describes the process of protein ubiquitination?

Accepted Answer

Ubiquitin is activated by E1, transferred to E2, and then attached to the substrate by E3 ligase.

Question 15

Which post-translational modification is most important for the determination of blood group antigens?

Accepted Answer

Glycosylation

Question 16

A protein is found to be polyubiquitylated. What is the most likely fate of this protein?

Accepted Answer

It will be targeted for degradation by the proteasome.

Question 17

Which of the following is a real-life example of phosphorylation regulating enzyme activity?

Accepted Answer

Activation of glycogen phosphorylase by phosphorylation

Question 18

Which post-translational modification is most commonly associated with the regulation of transcription and epigenetic silencing?

Accepted Answer

Methylation

Question 19

Which of the following is TRUE regarding the reversibility of post-translational modifications?

Accepted Answer

Some PTMs, such as phosphorylation and ubiquitination, are reversible and can be removed by specific enzymes.

Question 20

Which of the following best describes the effect of glycosylation on protein folding in the endoplasmic reticulum?

Accepted Answer

Glycosylation acts as a quality control mechanism to ensure only properly folded proteins are trafficked to the Golgi.

Fundamentals of Protein Structure: Post-Translational Modifications (PTMs)

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