GRE Subject Test: Biology : Understanding mRNA and Protein Modifications
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Example Questions
Example Question #57 : Genetics, Dna, And Molecular Biology
Which of the following post-transcriptional modifications occur in the nucleus?
I. 5' capping
II. Splicing
III. Polyadenylation
II and III
I and III
I, II, and III
I and II
I, II, and III
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 #58 : Genetics, Dna, And Molecular Biology
Which of the following post-translation modifications cannot be classified as lipidation?
Ubiquitination
Addition of GPI-anchor
Myristoylation
Palmityolation
Prenylation
Ubiquitination
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 #1 : 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?
Coupling mRNA to the spliceosome
Protection against degradation in the cytoplasm
Initiation of transcription
Transport of mRNA into the nucleus
Enhancement of intron splicing
Protection against degradation in the cytoplasm
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?
Lipoylation
Gamma-carboxylation
Palmitoylation
Ubiquitination
Acylation
Ubiquitination
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.
Methylation
5' capping
Polyadenylation
mRNA splicing
Ribonucleation
Polyadenylation
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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