GRE Subject Test: Biology : Understanding mRNA and Protein Modifications

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding M Rna And Protein Modifications

Which of the following post-transcriptional modifications occur in the nucleus?

I. 5' capping

II. Splicing

III. Polyadenylation

Possible Answers:

I and III

II and III

I and II

I, II, and III

Correct answer:

I, II, and III

Explanation:

All of the post-transcriptional modifications listed occur in the nucleus. Each is important in the process of turning pre-mRNA into mature mRNA that can successfully exit the nucleus and enter into translation. These modifications allow for the appropriate recognition by ribosomes and serve to enhance the stability of the mRNA molecule.

The 5' guanosine cap is added to one end of the RNA strand, and a poly-A tail is added to the other. These modifications serve to help with ribosome recognition and prevent degradation. Spicing involves the removal of non-coding introns from the RNA transcript, allowing for translation of the proper sequence.

Example Question #2 : Understanding M Rna And Protein Modifications

Which of the following post-translation modifications cannot be classified as lipidation?

Possible Answers:

Myristoylation

Prenylation

Ubiquitination 

Palmityolation

Addition of GPI-anchor

Correct answer:

Ubiquitination 

Explanation:

Ubiquitination is the only option in which the modification to the protein does not include the binding of a lipid group to a protein. Rather, it is the addition of another peptide to the existing protein.

Example Question #3 : Understanding M Rna And Protein Modifications

The process of polyadenylation results in the addition of a poly-A tail to mRNA after transcription. The poly-A tail consists of approximately 150-200 adenine bases at the 3' end of the mRNA. Which of the following best describes the purpose of polyadenylation in mRNA processing?

Possible Answers:

Protection against degradation in the cytoplasm

Transport of mRNA into the nucleus

Enhancement of intron splicing

Coupling mRNA to the spliceosome

Initiation of transcription

Correct answer:

Protection against degradation in the cytoplasm

Explanation:

Polyadenylation results in a long chain of adenosine monophosphate residues being added to the 3' end of a pre-mRNA as transcription is terminating. The poly-A tail provides stability to the mRNA molecule as it is transported through the cell to its ultimate location. Without this modification, the shorter mRNA would be degraded by enzymes within the cytoplasm. The other functions listed as answers are in no part dependent on the poly-A tail. 

Example Question #4 : Understanding M Rna And Protein Modifications

Which of the following post-translational modifications has most typically been associated with protein degradation via activation of the cell's proteasome system? 

Possible Answers:

Acylation

Ubiquitination

Gamma-carboxylation

Palmitoylation

Lipoylation

Correct answer:

Ubiquitination

Explanation:

Conjugation of ubiquitin molecules to a protein activates the ubiquitin proteasome system, which is required by cells to break down proteins into their component amino acid residues to be reallocated in protein building as necessary. While the other modifications may contribute to some degradation pathway, ubiquitin is classically considered a marker of protein destruction via the proteasome system. 

Example Question #5 : Understanding M Rna And Protein Modifications

__________ is the addition of a long tail of adenine bases to an mRNA during mRNA processing, and this step is crucial for the stability of the mRNA as it gets exported to other parts of the cell.

Possible Answers:

Methylation

Ribonucleation

mRNA splicing

Polyadenylation

5' capping

Correct answer:

Polyadenylation

Explanation:

Polyadenylation is the process in which a "Poly-a tail," or a tail of adenine bases, is added to the 3' end of an mRNA. The other processes listed do not carry out this function.

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