GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Protein Degradation

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

varsity tutors app store varsity tutors android store

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

1 Diagnostic Test 201 Practice Tests Question of the Day Flashcards Learn by Concept

Example Questions

Example Question #1 : Help With Protein Degradation

Which of the following are means of controlling protein concentrations?

Possible Answers:

RNAi

Gene silencing

Polyubiquination 

All of these are means of controlling protein concentration

Correct answer:

All of these are means of controlling protein concentration

Explanation:

All of the given answers are ways that a cell may regulate protein concentrations. Polyubiquination is a signal for the protein to be degraded by a proteasome. Gene silencing will prevent transcription, which will lower the amount of mRNA template that can be translated into a protein. RNAi will degrade specific mRNAs or prevent the translation of specific mRNAs into proteins.

Example Question #2 : Help With Protein Degradation

Proteins are brought to a __________ for degradation after they undergo __________

Possible Answers:

lysosome . . . glycosylation

proteasome . . . glycosylation

proteasome . . . polyubiquination

lysosome . . . polyubiquination

Correct answer:

proteasome . . . polyubiquination

Explanation:

Polyubiquination is a modification results from the binding of small ubiquitin residues to a protein. Polyubiquination of a protein signals damage or problems with functionality, and triggers the mechanisms that result in protein degradation. The polyubiquinated protein is then brought to a proteasome (a complex of proteins) that will degrade the protein.

Glycosylation involves the attachment of a carbohydrate complex to a protein. The identity of the carbohydrate is essential for determining the functional outcome of glycosylation, but generally results in signaling and transport labels for the protein. Glycosylation is not by itself a signal to be brought to either a proteasome or a lysosome.

Example Question #3 : Help With Protein Degradation

Which of the following answers best describes the sequence of events carried out by enzymes E1, E2, and E3 in the ubiquitin-proteasome pathway?

Possible Answers:

E1 senses cellular stress and activates E2, which phosphorylates E3 to conjugate ubiquitin to proteins to target them for post-translational modifications like acetylation. 

E1 transfers ATP to target proteins, E2 processes target proteins, and E3 degrades proteins through ATP-dependent complexes. 

E1 activates autophagosomes which fuse with proteins marked for degradation. E2 adds ubiquitin molecules to proteins within the autophagosome, and E3 activates acids to degrade the marked proteins. 

E1, E2, and E3 are all redundant in their activity within the protein destruction pathway; each covalently attach ubiquitin to target proteins to mark them for degradation by the proteasome. 

E1 activates ubiquitin molecules, E2 carries activated ubiquitin molecules to E3, and E3 covalently attaches activated ubiquitin molecules to a protein to mark it for degradation by a protease complex.

Correct answer:

E1 activates ubiquitin molecules, E2 carries activated ubiquitin molecules to E3, and E3 covalently attaches activated ubiquitin molecules to a protein to mark it for degradation by a protease complex.

Explanation:

E1, E2, and E3 all have unique activities that progress step-wise to activate ubiquitin and then attach those ubiquitins to mark a protein for degradation. Their functions are not redundant, nor do they activate acids, autophagosomes or ATP complexes over the course of their pathways. 

Example Question #4 : Help With Protein Degradation

Ubiquitination of a protein is one way to mediate protein degradation, however, ubiquitination is only a signal. What is ultimately responsible for ubiquitin-mediated degradation of a protein?

Possible Answers:

Peroxisome

None of these

Proteasome

Lysosome

Hydrolysis

Correct answer:

Proteasome

Explanation:

The correct answer is proteasome. Ubiquitination of a protein signals for the proteasome to degrade it and recycle the ubiquitin. Alternatively, the lysosome does degrade proteins, however, this process is independent of ubiquitin. The peroxisome is responsible for the degradation of fatty acids, certain amino acids, and reactive oxygen species. Hydrolysis simply refers to a chemical mechanism that splits apart a compound by the addition of water, it does not however, describe an organelle or cellular compartment that is reponsible for protein degradation. 

Example Question #5 : Help With Protein Degradation

The ubiquitin-mediated protein degradation process targets proteins to which cellular structure for degradation? 

Possible Answers:

Vesicle 

Golgi

Proteasome

Endoplasmic reticulum

Lysosome 

Correct answer:

Proteasome

Explanation:

The correct answer is proteasome. There are two general protein degradation processes: the first involving the lysosome and the second involving the proteasome. Lysosomal protein degradation is non-selective and occurs during cell starvation. Degradation through the proteasome is dependent on ubiquitination of the target protein, and as such, ensures protein-specific degradation. 

Example Question #6 : Help With Protein Degradation

How does ubiquitination of a protein facilitate its degradation? 

Possible Answers:

Recognition of ubiquitin by the proteasome

Promotes reprocessing through the Golgi apparatus

Recognition of ubiquitin by the lysosome

None of the other answers 

Promotes exocytosis of the protein

Correct answer:

Recognition of ubiquitin by the proteasome

Explanation:

The correct answer is recognition of ubiquitin by the proteasome. Ubiquitin-mediated protein degradation by the proteasome is a well characterized method of specific protein degradation. The protein targeted for degradation is phosphorylated, then ubiquitinated. The proteasome recognizes these distinct ubiquitin chains and degrades the protein. Protein degradation can also occur through the lysosome, but this is independent of ubiquitination and is less specific. The golgi complex is involved in protein folding and modification of recently translated amino acid chains. 

Example Question #7 : Help With Protein Degradation

What is the difference between proteolysis and ubiquitin-mediated protein degradation? 

Possible Answers:

Proteolysis occurs in only in the nucleus, but ubiquitin-mediated protein degradation occurs only in the cytoplasm

These two processes are synonymous 

Proteolysis occurs in the lysosome but ubiquitin-mediated protein degradation is in the proteasome

Proteolysis is the degradation of organelles whereas proteins are degraded through ubiquitin-dependent mechanisms

Correct answer:

Proteolysis occurs in the lysosome but ubiquitin-mediated protein degradation is in the proteasome

Explanation:

The correct answer is that proteolysis occurs in the lysosome but ubiquitin-mediated protein degradation is in the proteasome. Proteolysis-lysosomal degradation is non-selective and is activated upon cellular starvation. ubiquitin-mediated protein degradation is highly specific and functions to promote a wide range of cellular processes. 

Example Question #8 : Help With Protein Degradation

Which of the following additions to a protein will signal the cell to degrade it?

Possible Answers:

Ubiquitination

Glycosylation

Hydroxylation

Glycation

Correct answer:

Ubiquitination

Explanation:

Older proteins in our bodies need to be degraded once they become damaged or no longer necessary. One way that the cell tags these proteins is by adding a ubiquitin tag, which can then be recognized by a proteasome, leading to the proteins' deconstruction.

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

1 Diagnostic Test 201 Practice Tests Question of the Day Flashcards Learn by Concept
Learning Tools by Varsity Tutors

Incompatible Browser

Please upgrade or download one of the following browsers to use Instant Tutoring: