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Question
Which of the following statements explains why methotrexate is effective as a cancer chemotherapeutic?a. it serves as an analog of p-aminobenzoic acid and block bacterial synthesis of folate
b. acts as an inhibitor of dihydrofolate reductase, thus preventing production of tetrahydrofolate
c. it acts as a suicide substrates for the enzyme dihydropteroate synthetase
d. prevents the conversion of N5,N10-methenyl THF to N10-formyl THF which is required in 2 steps of the purine synthesis pathway
e. both b and d are correct
Answer
This answer is hidden. It contains 1 characters.
Related questions
Q:
In general, proteins whose folding is chaperone-dependent start the folding process first with ____ and then are passed as ____ folded intermediates to ____.
a. Hsp40; un-; Hsp70
b. Hsp90; un-; chaperonin
c. Hsp70; partially; chaperonin
d. Hsp40; partially; Hsp70
e. Hsp60; partially; Hsp40
Q:
Which of the following is responsible for Alzheimer's disease?
a. polyglutamine aggregates
b. neurofibrillary tangles of polymeric microtubule-binding protein tau
c. extracellular deposits of amyloid-ï¢ and intracellular neurofibrillary tangles of microtubule-binding protein tau
d. mutation in the huntingtin gene
e. none of the above
Q:
Which of the following correctly describes the order of events in the class I aminoacyl-tRNA synthetase reaction?I. displacement of AMPII. transesterificationIII. nucleophilic attack by 2'-hydroxyl of the tRNA on the acyl adenylateIV. formation of acyl adenylate by reaction of amino acid with ATPV. displacement and subsequent hydrolysis of pyrophosphatea. III, I, IV, V, IIb. III, V, IV, I, IIc. IV, II, I, III, Vd. IV, V, III, I, IIe. IV, I, III, II, V
Q:
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 moleculeb. 3'-hydroxyl of the nucleotide on the 5' end of the tRNA moleculec. 2'-hydroxyl of the nucleotide on the 5' end of the tRNA moleculed. 3'-hydroxyl of the nucleotide on the 3' end of the tRNA moleculee. 2'-hydroxyl of the nucleotide on the 3' end of the tRNA molecule
Q:
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
Q:
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
Q:
Termination of translation in prokaryotic cells requires:
a. binding of the terminator tRNA to the termination codon.
b. interaction of release factors with the termination codon.
c. ternary interaction of the release factor and the termination tRNA with the termination codon.
d. release factor interaction with the Shine-Dalgarno sequence and subsequent dissociation of the two ribosomal subunits.
e. displacement of EF-G by EF-Tu:aminoacyl-tRNA.
Q:
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.
Q:
Which of the following statements is true regarding the formylmethionine that serves as the first amino acid in bacterial protein synthesis?
a. the formyl group is removed during protein synthesis leaving methionine as the first residue in all bacterial proteins
b. the tRNA that carries formylmethionine is the same tRNA for methionine
c. the formyl group donor is N10-formyl-tetrahydrofolate
d. an aminoacyl-tRNA synthetase that is specific for formylmethionine attaches formylmethionine to the tRNA
e. none of the above.
Q:
Mitochondrial and chloroplastic ribosomes resemble ____ ribosomes.
a. prokaryotic
b. lower eukaryotic
c. higher eukaryotic
d. no other
e. none are true
Q:
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
Q:
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
Q:
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
Q:
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
Q:
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.
Q:
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
Q:
The araBAD operon allows for the use of what metabolite by E. coli?
a. arachidonic acid
b. arabinose
c. allose
d. altrose
e. none of the above
Q:
Spliceosomes include all of the following EXCEPT:
a. snRNPs.
b. RNA-annealing proteins.
c. ATP-dependent RNA-unwinding proteins.
d. enzymes catalyzing transesterification of phosphoesters.
e. all are components.
Q:
Transcription of a typical gene encoding a polypeptide in eukaryotes involves all of the following EXCEPT:
a. the splicing together of a number of exons in the DNA prior to transcription.
b. synthesis by RNA polymerase II.
c. transcription of DNA corresponding to both introns and exons.
d. transcription of the DNA which encodes the N-terminal of the polypeptide prior to DNA encoding to the C-terminal.
e. addition of the poly(A)+ tail.
Q:
The base-pair edges in the ____ groove act as a(n) ____ identifiable through ____ with specific proteins.
a. minor; enhancer; H-bonding
b. minor; recognition matrix; H-bonding
c. major; recognition matrix; H-bonding
d. major; repressor; ionic binding
e. major; transcriptional silencer; ionic bonding
Q:
The eukaryotic transcription factor that exhibits a sequence specificity for the TATA box is:
a. TFIIB.
b. TFIIC.
c. TFIID/TBP.
d. RNA polymerase II.
e. TFIIH.
Q:
All are correct about enhancer sequences in eukaryotic cells EXCEPT:
a. they can occur either upstream or downstream of the gene.
b. they can be in either orientation (bi-directional).
c. enhancer function is dependent on recognition by a specific transcription factor.
d. specific transcription factor binding at an enhancer stimulates transcription by interacting with RNA polymerase II.
e. all are correct.
Q:
All are characteristics of catabolic activator protein (CAP) EXCEPT:
a. ensures that the operons necessary for metabolism for alternate energy sources remains repressed until the supply of glucose is exhausted.
b. overrides the influence of any inducer that might be present.
c. cAMP enhances CAP's affinity for DNA.
d. N-terminal end binds cAMP and C-terminal end binds DNA.
e. all are true.
Q:
Characteristics of rho factor include all EXCEPT that it:a. recognizes and binds C-rich regions of RNA transcripts.b. binding regions must be ribosome free.c. advances in the 5'->3' direction to the transcription bubble.d. unwinds transcript and template to free nascent RNA.e. all are true.
Q:
The base in DNA that specifies the first base in the RNA transcript is called a(n) ____ and is numbered ____.a. promoter; -5b. enhancer; -35c. transcription start site; 0d. transcription start site; +1e. promoter complex; +5
Q:
Which of the following would most likely cause a frameshift mutation?
a. an alkylating agent such as methyl iodide
b. a base analog such as 5-bromouracil
c. a chemical mutagen such as nitrous acid
d. an intercalation agent such as acridine orange
e. none of the above
Q:
Which of the following statements explains why the adenine analog, 2-aminopurine (2-AP), can cause mutations in DNA when it is inserted in place of a site normally occupied by A?
a. 2-AP forms 2 hydrogen bonds with thymine
b. 2-AP undergoes oxidative deaminiation to hypoxanthine which basepairs with C
c. 2-AP can form a single hydrogen bond with C
d. 2-AP is often found as a schiff base that crosslinks with T
e. none of the above
Q:
Misincorporation of all subsequent amino acids results from ____ mutations.
a. chemical
b. base shift
c. frameshift
d. transition
e. all are true
Q:
Mutations in DNA may result from all of the following EXCEPT:
a. spontaneous mutations due to errors in replication.
b. physical insults on the cell, such as UV light.
c. errors in transcription.
d. chemical mutagens.
e. introduction of a base analog into DNA.
Q:
A transition mutation would be replacing A by:
a. T.
b. C.
c. U.
d. G.
e. either T or C