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Which of the following is not a phase in translation?
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.
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Which of the following is not a type of modification that can occur after translation?
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.
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Which of the following ensures that viral gene translation occurs even when host translation is inhibited?
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.
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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?
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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Which amino acid is the "start" amino acid in a peptide chain?
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.
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