Chapter 9 Reading Assignment

Which of the following steps in translation is NOT facilitated by elongation factors? A) Recruitment of charged tRNAs to the A-site B) Translocation of the ribosome along the mRNA. C) Binding of initiator tRNA to the AUG start codon D) All of the above.

C) Binding of initiator tRNA to the AUG start codon Binding of initiator tRNA to the start codon is facilitated by initiation factors.

Ribosomal subunits are large complexes composed of numerous polypeptides and at least one rRNA molecule. Which subunits include three rRNA molecules? A) Bacterial large subunits B) Prokaryotic small subunits C) Eukaryotic large subunits D) Eukaryotic small subunits

C) Eukaryotic large subunits Eukaryotic large ribosomal subunits include three rRNAs (28S, 5.8S, and 5S in mammals).

What is the Shine-Dalgarno sequence? A) a short conserved nucleotide sequence upstream of the AUG start codon that binds initiator tRNA B) a conserved nucleotide sequence that identifies a transcriptional start site C) a short conserved nucleotide sequence downstream of the stop codon that signals termination of translation D) a short conserved nucleotide sequence upstream of the AUG start codon that serves to align the mRNA on the bacterial small ribosomal subunit

D) a short conserved nucleotide sequence upstream of the AUG start codon that serves to align the mRNA on the bacterial small ribosomal subunit The Shine-Dalgarno sequence is a purine-rich sequence of six nucleotides localized three to nine nucleotides upstream of the AUG start codon.

What is a charged tRNA? A) a tRNA that is bound to an initiation factor (IF) B) a tRNA that is bound to the small ribosomal subunit C) an ionic form of a tRNA D) a tRNA that carries a specific amino acid

D) a tRNA that carries a specific amino acid

What is polycistronic mRNA? A) mRNA that is present in many copies in the cell B) mRNA that includes multiple coding segments (exons) interrupted by intervening sequences (introns) C) mRNA that is being translated by multiple ribosomes simultaneously D) mRNA that encodes multiple different polypeptide products

D) mRNA that encodes multiple different polypeptide products See Figure 9.12.

In the early 1960s, a number of investigators conducted a series of elegant experiments that helped to decipher the genetic code. Which of the following describes a bona fide property of the genetic code? A) The genetic code consists of nonoverlapping codons. B) The genetic code consists of overlapping codons. C) Spacers or markers separate codons from one another. D) The genetic code is a doublet code composed of two nucleotides per codon.

A) The genetic code consists of nonoverlapping codons. Experiments by Hans Fraenkel-Conrat in 1960 demonstrated that the genetic code consists of nonoverlapping codons.

What is the final step of translational initiation in both bacteria and eukaryotes? A) Union of the large subunit with the small subunit to form the intact ribosome B) Binding of GTP to the intact ribosome C) Binding of the intact ribosome to the 5' cap on the mRNA D) Binding of the initiator tRNA to the AUG start codon

A) 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.

Aminoacyl-tRNA synthetases are the enzymes responsible for attaching the correct amino acid to the corresponding tRNA molecule. How many different tRNA synthetase enzymes are typically required to accomplish this task in the cell? A) 1 B) 20 C) 61 D) 64

B) 20 There is one tRNA synthetase enzyme for each amino acid. Each enzyme is responsible for charging all iso-accepting tRNAs with the specific corresponding amino acid.

What normally binds to an open A-site on the ribosome? A) The 3' UTR (untranslated region) of the mRNA B) A tRNA that carries the next amino acid to be added to the polypeptide chain C) The initiator tRNA that carries the first amino acid in the polypeptide chain D) An empty tRNA after its amino acid has been added to the polypeptide chain

B) A tRNA that carries the next amino acid to be added to the polypeptide chain

In the process of translational initiation in bacteria, where does the initiator tRNA first bind to the ribosome? A) to the partial P site on the large ribosomal subunit B) to the partial P site on the small ribosomal subunit C) to the partial A site on the small ribosomal subunit D) to the partial A site on the large ribosomal subunit

B) to the partial P site on the small ribosomal subunit See Figure 9.6.