GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Translation Processes
Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology
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Example Questions
Example Question #1 : Translation And Proteins
Which of the following is not a type of modification that can occur after translation?
Proteasomal degradation
Trimming
Phosphorylation
5' capping
5' capping
Post-translational modifications that may occur after a protein is translated include numerous processes to alter the structure or function of the protein. Trimming modification involves removal of the N- or C - terminal propeptides from zymogens to generate mature proteins. Covalent alterations, including phosphorylation, glycosylation and hydroxylation, are frequently used to modify the structure or energy state of a protein. Proteasomal degradation requires the attachment of ubiquitin to defective proteins to tag them for degradation and digestion. Amino acids from degraded proteins can often be recycled to generate new molecules.
5' capping occurs in the nucleus after transcription and is required for transport of RNA out of the nucleus prior to translation.
Example Question #3 : Translation And Proteins
Which of the following is not a phase in translation?
Termination
Modification
Elongation
Initiation
Modification
There are four phases in translation: activation, initiation, elongation, and termination. Activation is the process that joins the correct amino acid to the correct tRNA. When the tRNA has an amino acid bound to it, it is "charged." Initiation occurs when the small ribosomal subunit binds the 5' end of mRNA, with the help of initiation factors and other proteins. The structure then recruits a methionine tRNA to the start codon to begin the elongation process. Elongation occurs as charged tRNA molecules transfer their amino acids to the growing polypeptide. Termination results when a stop codon is recognized by release factors and the completed protein is released from the ribosome.
Modification of the transcript occurs after translation has been completed.
Example Question #8 : Translation And Proteins
Which of the following ensures that viral gene translation occurs even when host translation is inhibited?
5' untranslated region (UTR)
Promoter
Internal Ribosomal Entry Sites (IRES)
5' guanine cap
3' poly-A tail
Internal Ribosomal Entry Sites (IRES)
Viruses utilize IRES to allow translation to occur in a 5' cap-independent manner. Translational machinery (ribosomes) are located to the IRES so that translation can occur. 5' guanine cap and 3' poly-A tails are mRNA modifications that are normally necessary to initiate translation, but are cap-dependent. The promoter regulates genes expression on the level of transcription, whereas the 5' UTR regulates translation.
Example Question #7 : Translation And Proteins
Which amino acid is the "start" amino acid in a peptide chain?
Tyrosine
Threonine
Arginine
Methionine
Lysine
Methionine
The correct answer is methionine. The ATG codon triplet in a mRNA strand codes for the start of the peptide, and this first amino acid that is coded by ATG is methionine.
Example Question #11 : Translation And Proteins
Most translation occurs by a mRNA cap-dependent mechanism, however, translation can occur by cap-independent initiation. One mechanism by which eukaryotic cells can initiate cap-independent translation is by which of the following approaches?
5' mRNA cap
Internal ribosome entry site
Poly(A)-binding protein
elF4F initiation complex
None of these
Internal ribosome entry site
The correct answer is the internal ribosome entry site. This site is a specific nucleotide sequence that allows for translation initiation in the middle of a mRNA sequence, rather than at the 5' end, and does not require the cap-dependent elF4F initiation complex or the 5'cap. The poly(A)-binding protein complexes with the 3' end of mRNA strands during translation initiation via the cap-dependent mechanism.
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