Mastering Genetics Ch 9 Pre-Questions
Which region of a tRNA molecule binds to amino acids?
3' end The 3′ end of a tRNA molecule contains the amino acid binding site.
What normally binds to an open A-site on the ribosome?
A tRNA that carries the next amino acid to be added to the polypeptide chain
Ribosomal subunits are large complexes composed of numerous polypeptides and at least one rRNA molecule. Which subunits include three rRNA molecules?
Eukaryotic large subunits Eukaryotic large ribosomal subunits include three rRNAs (28S, 5.8S, and 5S in mammals).
True or False: The enzyme EF‑Tu catalyzes the formation of a peptide bond between the amino acid held by the tRNA in the A site and the elongating amino acid chain held by the tRNA in the P site.
False Peptidyl transferase is the enzyme that catalyzes the formation of peptide bonds during translation. EF‑Tu is an elongation factor that facilitates the entry of charged tRNAs into the A site.
Which of the following statements best describes the function of aminoacyl tRNA synthetase?
It attaches a specific amino acid to a tRNA molecule. Aminoacyl tRNA synthetase catalyzes the charging reaction that links a specific amino acid to a tRNA molecule.
What result would you expect if a mutation eliminates one of the four arms of a tRNA?
The tRNA will not be recognized by tRNA synthetase and cannot be charged.
True or False: Each aminoacyl tRNA synthetase is specific for one amino acid and a small number of tRNAs.
True Each aminoacyl tRNA synthetase enzyme recognizes only one amino acid, but each enzyme can often recognize several tRNAs because there is usually more than one codon for each amino acid.
What is the final step of translational initiation in both bacteria and eukaryotes?
Union of the large subunit with the small subunit to form the intact ribosome In both bacteria and eukaryotes, the final step in translational initiation is the union of the large and small ribosomal subunits, coupled with GTP hydrolysis and release of initiation factors.
What is a charged tRNA?
a tRNA that carries a specific amino acid
What event occurs during translocation?
mRNA shifts in the 5' direction along the ribosome. Translocation is the process by which mRNA shifts by 3 bases in the 5' direction along the ribosome to bring another codon into the A site.
In eukaryotes, the initiation factor proteins eIF1A and eIF3 join with a ________ carrying the amino acid ______ to form the preinitiation complex.
tRNA; methionine
A signal sequence at the N-terminus of newly synthesized proteins will direct the protein to the ________ for protein packaging.
endoplasmic reticulum
How many different aminoacyl-tRNA synthetases can be found in a given cell?
20
What molecule provides the energy to form charged tRNAs?
ATP
At which site does the charged initiator tRNA bind during protein synthesis?
P site The initiator tRNAfmet binds to the mRNA codon in the P site of the ribosome. The initiator tRNA is the only one that binds in the P site; all other tRNAs bind the ribosome in the A site.
In the unlikely event that a tRNA has been charged with the wrong amino acid, what high-fidelity enzyme is likely to blame?
aminoacyl synthetase
