Biochem ch 30

mikebewo's version from 2015-05-19 23:18


Question Answer
The adapter molecule that interacts specifically with both nucleic acids and amino acids is:
a. rRNA.
b. tRNA.
c. mRNA.
d. ssRNA.
e. all are true.
The linkage between the amino acid and the tRNA in an amino-acyl tRNA complex is:
a. an amide
b. an acyl phosphate
c. a hydroxylamine
d. an ether
e. an ester
The genetic code is said to be degenerate, which means that:
a. Each codon codes for more than one amino acid.
b. An anticodon can interact with more than one codon in the mRNA in which the codon may differ in any or all of the three nucleotides.
c. Most amino acids are coded for by more than one codon.
d. The code is universally used by virtually all species.
e. None are true.
Codons representing the same amino acid or chemically similar amino acids tend to be similar in sequence, often differing only in the third base. This feature is called:
a. home-base degeneracy.
b. first-base similarity.
c. second-base type similarity.
d. third-base degeneracy.
e. all are true.
Which of the following is/are true regarding the genetic code?
a. codons are read 5' to 3'
b. there are 20 total "sense" codons, one for each amino acid
c. there are three nonsense codons; these are "stop" signals
d. a and c are true
e. a, b, and c are true
An important difference between a class I and class II aminoacyl-tRNA synthetase is:
a. The two classes proceed through different aminoacyl-AMP intermediates.
b. Class I synthetases first attach the amino acid to the 2'-hydroxyl on ribose, whereas class II attach them to the 3'-hydroxyl.
c. Class I synthetases attach amino acids to the 5'-end of the tRNA, whereas class II attach them to the 3'-end.
d. The 5'-end of the tRNA molecule is phosphorylated only for those tRNAs recognized by class I synthetases.
e. None are true.
The anticodon of a tRNA is 5'UUG. What codon(s) can be theoretically recognized by this tRNA?
a. 5'CAA only
b. 5'CAA & 5'CAG
c. 5'AAC only
d. 5'AAC & 5' GAC
e. 5'CAC only
All of the statements about the tRNA molecule with the anticodon 5'CAU are correct EXCEPT:
a. It is the anticodon for tRNAfmet.
b. The wobble base in the anticodon would be cytosine.
c. Its anticodon can theoretically base pair with up to three different codons.
d. Its anticodon can base pair to the codon 5'AUG.
e. All are correct.
All members of a set of tRNAs specific for a particular amino acid - termed ____ tRNA - are served by one ____.
a. companion; codon family
b. companion; tRNA binding site
c. isoacid; tRNA family
d. isoacceptor; aminoacyl tRNA synthetase
e. none are true
Nonsense suppression is the production of isoacceptor tRNAs called ____ tRNAs that read ____ codons and insert an amino acid.
a. nonsense; nonsense
b. suppressor; nonsense
c. suppressor; suppressive
d. nonsense; suppressive
e. codon; anticodon
____ are the agents of protein synthesis.
a. Nuclei
b. Mitochondria
c. Chloroplasts
d. Ribosomes
e. Plasma membranes
Which of the following statements is true regarding ribosomes?
a. they are found in the cytosol and nucleus of all cells
b. prokaryotic ribosomes consist of a 30S and a 50S subunit while eukaryotic ribosomes consist of a 60S and an 80S subunit
c. ribosomes consist of both protein and ribonucleic acid with the majority of the mass from the protein component
d. since the peptidyl transferase activity is perfomed by RNA, it can be considered a ribozyme
e. all are true
Ribosomal proteins are typically rich in the amino acids ____ and ____ to interact with ____ RNAs.
a. asp; glu; polycationic
b. asp; ala; polycationic
c. lys; ala; polyanionic
d. ala; arg; polyanionic
e. arg; lys; polyanionic
Ribosomes constitute about ____ of the dry cell mass of an E. coli cell.
a. 1%
b. 5%
c. 10%
d. 20%
e. 40%
All are characteristics of ribosomal subunit assembly under appropriate conditions of pH and ionic strength EXCEPT:
a. ribosomes self-assemble spontaneously
b. no intervention by any additional factors or chaperones is required
c. ribosomal proteins bind in a specific order.
d. rRNA acts as a scaffold upon which various ribosomal proteins convene
e. all are true
The 30S subunit of E. coli ribosomes has all the following anatomical characteristics EXCEPT:
a. "head".
b. "body" or "base".
c. "platform".
d. "legs".
e. all are true.
Peptidyl transferase is the catalytic center of the ribosome and is located:
a. on the 30 S subunit near the decoding center.
b. on the 30 S subunit near the head.
c. on the 50 S subunit near the center protuberance.
d. on the 50 S subunit at the bottom of a deep cleft.
e. on the 50 S subunit at the cleft of the L7/L12 ridge.
Mitochondrial and chloroplastic ribosomes resemble ____ ribosomes.
a. prokaryotic
b. lower eukaryotic
c. higher eukaryotic
d. no other
e. none are true
All are components required for peptide chain initiation EXCEPT:
a. mRNA.
b. 30S and 50S ribosomal subunits.
c. initiation factors.
d. GTP and f-Met-tRNAifMet.
e. all are true.
Elongation factor Tu (EF-Tu):
a. binds GTP promoting translocation of ribosomes along mRNA.
b. displaces GDP from the elongation complex.
c. binds aminoacyl-tRNA in the presence of GTP.
d. binds initiator tRNA and GTP.
e. binds to 30 S subunit and drives mRNA binding.
Which of the following does not reqire GTP hydrolysis?
a. the formation of the initiation complex (translationally active 70 S ribosome complex).
b. the binding of the aminoacyl tRNA to the A site during elongation
c. translocation with release of the uncharged tRNA during elongation
d. the dissociation of release factors from the ribosome.
e. all of the above require GTP hydrolysis.
The actual peptide bond-forming step in translation is referred to as ____, and is catalyzed by ____.
a. peptide bond-formation; peptidase
b. transpeptidation; transpeptidase
c. peptidyl transfer; peptidyl transferase
d. translocation; translocase
e. none of the above
Peptidyl transferase catalyzes the reaction in which the nucleophile is:
a. oxygen in the carboxylate group of the aminoacyl-tRNA.
b. amino nitrogen in the aminoacyl-tRNA.
c. amino nitrogen from the peptidyl-tRNA.
d. oxygen in the carboxylate group of the peptidyl-tRNA.
e. electron pair on a ring N atom of the purine A2451.
The energy expenditure for protein synthesis is at least ____ high-energy phosphoric anhydride bonds per amino acid.
a. 0
b. 1
c. 2
d. 3
e. 4
The termination signal complex transforms the ribosomal peptidyl transferase into a/an:
a. lyase.
b. isomerase.
c. hydrolase.
d. transferase.
e. ligase.
Ribosome:mRNA:P-site tRNA complex, with the help of ____, is disassembled by ____ which is an excellent molecular mimic of a(n) ____.
a. ATP; tRNA terminator; GTP
b. tRNA; ribosome recycling factor; mRNA
c. EF-G; ribosome recycling factor; tRNA
d. mRNA; elongation factor; EF-G
e. none are true
Which of the following proteins is NOT correctly defined?
a. IF-2: G-protein that binds to the initial f-met tRNA
b. EF-Tu: G-protein that binds aminoacyl-tRNA
c. EF-Ts: G-protein that promotes translocation of mRNA
d. RF-3: G-protein that is a structural mimic of tRNA
e. all are true.
Intact 70S ribosomes are ____ in initiation of protein synthesis because ____ 30S subunits can interact with initiation factors.
a. active; bound
b. inactive; only free
c. active; open
d. inactive; mRNA bound
e. all are true
All are characteristics of eukaryotic mRNA EXCEPT:
a. poly (A) tail.
b. no Shine-Dalgarno sequence.
c. codon-binding directs for an initiator tRNA carrying met.
d. 5'-7methyl-GTP cap.
e. all are characteristics.
Each of the following statements regarding ways in which eukaryotic protein synthesis differs from prokaryotic protein synthesis is true EXCEPT:
a. prokaryote protein synthesis is initiated by f-Met, while eukaryotic is initiated by Met
b. prokaryotes use a 30S small ribosomal subunit, while eukaryotes use a 40S small ribosomal subunit
c. prokaryotic and eukaryotic translation initiation differ significantly in mechanism and process
d. prokaryotic termination involves three release factors, while eukaryotic termination involves one
e. all of the above are true statements
Which inhibitor of protein synthesis competes with aminoacyl-tRNAs for binding to the A-site of the ribosome?
a. puromycin
b. erythromycin
c. streptomycin
d. cycloheximide
e. tetracycline
A protein synthesis inhibitor that catalytically inactivates 28S rRNA and is very toxic in eukaryotic cells is:
a. ricin.
b. puromycin.
c. cycloheximide.
d. streptomycin.
e. tetracycline.
Diphtheria toxin is extremely potent and only a few micrograms causes death because it:
a. inhibits f-Met-tRNAimet binding.
b. is an enzyme and can catalytically modify a number of GTP-dependent enzymes.
c. inhibits translocation of peptidyl-tRNA.
d. catalyzes inactivation of 28 S tRNA.
e. inhibits EF-G:GTP dissociation from ribosomes.
In a class I aminoacyl-tRNA synthetase, which of the following reacts with the acyl phosphate formed during the reaction of ATP with the amino acid?
a. 5′-hydroxyl of the nucleotide on the 5′ end of the tRNA molecule
b. 3′-hydroxyl of the nucleotide on the 5′ end of the tRNA molecule
c. 2′-hydroxyl of the nucleotide on the 5′ end of the tRNA molecule
d. 3′-hydroxyl of the nucleotide on the 3′ end of the tRNA molecule
e. 2′-hydroxyl of the nucleotide on the 3′ end of the tRNA molecule
Which of the following correctly describes the order of events in the class I aminoacyl-tRNA synthetase reaction?

I. displacement of AMP
II. transesterification
III. nucleophilic attack by 2′-hydroxyl of the tRNA on the acyl adenylate
IV. formation of acyl adenylate by reaction of amino acid with ATP
V. displacement and subsequent hydrolysis of pyrophosphate

a. III, I, IV, V, II
b. III, V, IV, I, II
c. IV, II, I, III, V
d. IV, V, III, I, II
e. IV, I, III, II, V

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