ch16-18 Flashcards - Easy Notecards

1) In his transformation experiments, what did Griffith observe?
A) Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.
B) Mixing a heat-killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic.
C) Infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains.
D) Mice infected with a pathogenic strain of bacteria can spread the infection to other mice.

2) How do we describe transformation in bacteria?
A) the creation of a strand of DNA from an RNA molecule

B) the creation of a strand of RNA from a DNA molecule

C) the infection of cells by a phage DNA molecule

D) assimilation of external DNA into a cell

4) In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?
A) DNA contains sulfur, whereas protein does not.
B) DNA contains phosphorus, whereas protein does not.

C) DNA contains nitrogen, whereas protein does not.
D) DNA contains purines, whereas protein includes pyrimidines.

5) Which of the following investigators was (were) responsible for the following discovery?
In DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine.
A) Alfred Hershey and Martha Chase
B) Oswald Avery, Maclyn McCarty, and Colin MacLeod
C) Erwin Chargaff
D) Matthew Meselson and Franklin Stahl

7) It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in which of the following?

A) sequence of bases
B) phosphate-sugar backbones

C) complementary pairing of bases
D) side groups of nitrogenous bases

10) Hershey and Chase set out to determine what molecule served as the unit of inheritance. They completed a series of experiments in which E. coli was infected by a T2 virus. Which molecular component of the T2 virus actually ended up inside the cell?
A) protein

B) RNA
C) ribosome
D) DNA

11) In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and _____ of the last nucleotide in the polymer.
A) the 5' phosphate
B) C6

C) the 3' OH
D) a nitrogen from the nitrogen-containing base

12) Replication in prokaryotes differs from replication in eukaryotes for which of the following reasons?
A) Prokaryotic chromosomes have histones, whereas eukaryotic chromosomes do not.
B) Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.

C) The rate of elongation during DNA replication is slower in prokaryotes than in eukaryotes.

D) Prokaryotes produce Okazaki fragments during DNA replication, but eukaryotes do not.

14) Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?
A) One of the daughter cells, but not the other, would have radioactive DNA.
B) Neither of the two daughter cells would be radioactive.
C) All four bases of the DNA would be radioactive.
D) DNA in both daughter cells would be radioactive.

15) In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin. Which of the following would you expect as a result of this mutation?
A) Additional proofreading will occur.
B) No replication fork will be formed.

C) Replication will occur via RNA polymerase alone.
D) Replication will require a DNA template from another source.

16) In E. coli, which enzyme catalyzes the elongation of a new DNA strand in the 5' → 3' direction?
A) primase
B) DNA ligase

C) DNA polymerase III
D) helicase

17) Eukaryotic telomeres replicate differently than the rest of the chromosome. This is a consequence of which of the following?
A) the evolution of telomerase enzyme
B) DNA polymerase that cannot replicate the leading strand template to its end

C) gaps left at the 5' end of the lagging strand
D) gaps left at the 3' end of the lagging strand because of the need for a primer

18) How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?
A) It adds a single 5' cap structure that resists degradation by nucleases.
B) It causes specific double-strand DNA breaks that result in blunt ends on both strands.
C) It catalyzes the lengthening of telomeres, compensating for the shortening that could occur during replication without telomerase activity.

D) It adds numerous GC pairs, which resist hydrolysis and maintain chromosome integrity.

19) The DNA of telomeres has been highly conserved throughout the evolution of eukaryotes. This most likely reflects _____.
A) the low frequency of mutations occurring in this DNA
B) continued evolution of telomeres

C) that new mutations in telomeres have been advantageous

D) a critical function of telomeres

20) At a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork:

3' CCTAGGCTGCAATCC 5'
An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?
A) 5' GCCTAGG 3'
B) 5' ACGTTAGG 3'
C) 5' ACGUUAGG 3'
D) 5' GCCUAGG 3'

21) In E. coli, to repair a thymine dimer by nucleotide excision repair, in which order do the necessary enzymes act?
A) nuclease, DNA polymerase III, RNA primase
B) helicase, DNA polymerase I, DNA ligase

C) DNA ligase, nuclease, helicase
D) nuclease, DNA polymerase I, DNA ligase

22) In E. coli, what is the function of DNA polymerase III?

A) to unwind the DNA helix during replication
B) to seal together the broken ends of DNA strands
C) to add nucleotides to the 3' end of a growing DNA strand

D) to degrade damaged DNA molecules

24) The leading and the lagging strands differ in that _____.
A) the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction
B) the leading strand is synthesized by adding nucleotides to the 3' end of the growing strand, and the lagging strand is synthesized by adding nucleotides to the 5' end
C) the lagging strand is synthesized continuously, whereas the leading strand is synthesized in short fragments that are ultimately stitched together
D) the leading strand is synthesized at twice the rate of the lagging strand

25) A new DNA strand elongates only in the 5' to 3' direction because _____.
A) DNA polymerase begins adding nucleotides at the 5' end of the template
B) the polarity of the DNA molecule prevents addition of nucleotides at the 3' end

C) replication must progress toward the replication fork
D) DNA polymerase can add nucleotides only to the free 3' end

27) What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?
A) It synthesizes RNA nucleotides to make a primer.
B) It joins Okazaki fragments together.

C) It unwinds the parental double helix.
D) It stabilizes the unwound parental DNA.

28) Which of the following help(s) to hold the DNA strands apart while they are being replicated?
A) primase
B) ligase

C) DNA polymerase
D) single-strand DNA binding proteins

29) Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. This occurs because their cells cannot_____.
A) replicate DNA
B) undergo mitosis

C) exchange DNA with other cells
D) repair thymine dimers

30) Which of the following would you expect of a eukaryote lacking telomerase?

A) a high probability of somatic cells becoming cancerous
B) an inability to produce Okazaki fragments
C) an inability to repair thymine dimers

D) a reduction in chromosome length in gametes

35) Within a double-stranded DNA molecule, adenine forms hydrogen bonds with thymine and cytosine forms hydrogen bonds with guanine. This arrangement _____.
A) allows variable width of the double helix
B) permits complementary base pairing

C) determines the tertiary structure of a DNA molecule

D) determines the type of protein produced

38) Who performed classic experiments that supported the semiconservative model of DNA replication?
A) Watson and Crick
B) Meselson and Stahl

C) Hershey and Chase
D) Franklin and Wilkins

39) DNA contains the template needed to copy itself, but it has no catalytic activity in cells. What catalyzes the formation of phosphodiester bonds between adjacent nucleotides in the DNA polymer being formed?
A) ribozymes
B) DNA polymerase
C) ATP
D) deoxyribonucleotide triphosphates

40) What provides the energy for the polymerization reactions in DNA synthesis?

A) ATP
B) DNA polymerase
C) breaking the hydrogen bonds between complementary DNA strands

D) the deoxyribonucleotide triphosphate substrates

44) What is a telomere?
A) the mechanism that holds two sister chromatids together

B) DNA replication during telophase
C) the site of origin of DNA replication
D) the ends of linear chromosomes

45) Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span of cultured human cells. How might adding telomerase affect cellular aging?
A) Telomerase will speed up the rate of cell proliferation.

B) Telomerase eliminates telomere shortening and retards aging.

C) Telomerase shortens telomeres, which delays cellular aging.

D) Telomerase would have no effect on cellular aging.

46) Telomere shortening is a problem in which types of cells?

A) only prokaryotic cells
B) only eukaryotic cells
C) cells in prokaryotes and eukaryotes

47) Which of the following cells have reduced or very little active telomerase activity?

A) most normal somatic cells
B) most normal germ cells
C) most cancer cells

48) Researchers found E. coli that had mutation rates one hundred times higher than normal. Which of the following is the most likely cause of these results?
A) The single-stranded binding proteins were malfunctioning.
B) There were one or more mismatches in the RNA primer.

C) The proofreading mechanism of DNA polymerase was not working properly.
D) The DNA polymerase was unable to add bases to the end of the growing nucleic acid chain.

49) In a healthy cell, the rate of DNA repair is equal to the rate of DNA mutation. When the rate of repair lags behind the rate of mutation, what is a possible fate of the cell?
A) The cell can be transformed to a cancerous cell.
B) RNA may be used instead of DNA as inheritance material.

C) The cell will become embryonic.
D) DNA synthesis will continue by a new mechanism.

50) Which of the following statements describes a eukaryotic chromosome?
A) a single strand of DNA
B) a series of nucleosomes wrapped around two DNA molecules
C) a chromosome with different numbers of genes in different cell types of an organism

D) a single linear molecule of double-stranded DNA plus proteins

51) If a cell were unable to produce histone proteins, which of the following would be a likely effect?
A) There would be an increase in the amount of "satellite" DNA produced during centrifugation.

B) The cell's DNA couldn't be packed into its nucleus.

C) Spindle fibers would not form during prophase.
D) Amplification of other genes would compensate for the lack of histones.

52) Which of the following statements is true of histones?
A) Each nucleosome consists of two molecules of histone H1.
B) Histone H1 is not present in the nucleosome bead; instead, it draws the nucleosomes together.

C) The carboxyl end of each histone extends outward from the nucleosome and is called a "histone tail."
D) Histones are found in mammals, but not in other animals or in plants or fungi.

53) Why do histones bind tightly to DNA?
A) Histones are positively charged, and DNA is negatively charged.

B) Histones are negatively charged, and DNA is positively charged.

C) Both histones and DNA are strongly hydrophobic.
D) Histones are covalently linked to the DNA.

54) Which of the following represents the order of increasingly higher levels of organization of chromatin?
A) nucleosome, 30-nm chromatin fiber, looped domain
B) looped domain, 30-nm chromatin fiber, nucleosome

C) nucleosome, looped domain, 30-nm chromatin fiber

D) 30-nm chromatin fiber, nucleosome, looped domain

56) Which of the following is most critical for the association between histones and DNA? A) Histones are small proteins.
B) Histones are highly conserved (that is, histones are very similar in every eukaryote).
C) There are at least five different histone proteins in every eukaryote.

D) Histones are positively charged.

57) In E. coli replication the enzyme primase is used to attach a 5 to 10 base ribonucleotide strand complementary to the parental DNA strand. The RNA strand serves as a starting point for the DNA
polymerase that replicates the DNA. If a mutation occurred in the primase gene, which of the following would you expect?
A) Replication would only occur on the leading strand.
B) Replication would only occur on the lagging strand.
C) Replication would not occur on either the leading or lagging strand.
D) Replication would not be affected as the enzyme primase in involved with RNA synthesis.

58) Hershey and Chase used a DNA-based virus for their work. What would the results have been if they had used an RNA virus?
A) With an RNA virus radioactive protein would have been in the final pellet.
B) With an RNA virus radioactive RNA would have been in the final pellet.

C) With an RNA virus neither sample would have had a radioactive pellet.
D) With an RNA virus the protein shell would have been radioactive in both samples.

59) The lagging strand is characterized by a series of short segments of DNA (Okazaki fragments) that will be joined together to form a finished lagging strand. The experiments that led to the discovery of Okazaki
fragments gave evidence for which of the following ideas?
A) DNA polymerase is a directional enzyme that synthesizes leading and lagging strands during replication.
B) DNA is a polymer consisting of four monomers: adenine, thymine, guanine, and cytosine.

C) DNA is the genetic material.
D) Bacterial replication is fundamentally different from eukaryotic replication. The key shouldn’t be way longer than the distractors.

42) What is the difference between the leading strand and the lagging strand in DNA replication?

A) The leading strand is synthesized in the 3' → 5' direction in a discontinuous fashion, while the lagging strand is synthesized in the 5' → 3' direction in a continuous fashion.
B) The leading strand is synthesized continuously in the 5' → 3' direction, while the lagging strand is synthesized discontinuously in the 5' → 3' direction.

C) The leading strand requires an RNA primer, whereas the lagging strand does not.
D) There are different DNA polymerases involved in elongation of the leading strand and the lagging strand.

43) What is a major difference between eukaryotic DNA replication and prokaryotic DNA replication?
A) Prokaryotic replication does not require a primer.
B) Prokaryotic chromosomes have a single origin of replication, while eukaryotic chromosomes have multiple origins of replication.

C) DNA replication in prokaryotic cells is conservative. DNA replication in eukaryotic cells is semi-conservative.

D) DNA polymerases of prokaryotes can add nucleotides to both 3' and 5' ends of DNA strands while those of eukaryotes function only in the 5' → 3' direction.

3) The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following?
A) A gene from an organism can theoretically be expressed by any other organism.
B) DNA was the first genetic material.

C) The same codons in different organisms translate into different amino acids.

D) Different organisms have different types of amino acids.

4) The figure above shows a simple metabolic pathway. According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway?
A) 1
B) 2

C) 3
D) It cannot be determined from the pathway.

5) Refer to the metabolic pathway illustrated above. If A, B, and C are all required for growth, a strain that is mutant for the gene-encoding enzyme A would be able to grow on medium supplemented with _____.
A) nutrient A only

B) nutrient B only

C) nutrient C only

D) nutrients A and C

6) Refer to the metabolic pathway illustrated above. If A, B, and C are all required for growth, a strain mutant for the gene-encoding enzyme B would be able to grow on medium supplemented with _____.
A) nutrient A only

B) nutrient B only

C) nutrient C only

D) nutrients A and C

10) Which of the following contradicts the one-gene, one-enzyme hypothesis?
A) A mutation in a single gene can result in a defective protein.
B) Alkaptonuria results when individuals lack a single enzyme involved in the catalysis of homogentisic acid.
C) Sickle-cell anemia results in defective hemoglobin.
D) A single antibody gene can code for different related proteins, depending on the splicing that takes place post-transcriptionally.

11) Which of the following is directly related to a single amino acid?

A) the base sequence of the tRNA
B) the amino acetyl tRNA synthase
C) the three-base sequence of mRNA

D) the complementarity of DNA and RNA

12) In the process of transcription, _____.

A) DNA is replicated
B) RNA is synthesized
C) proteins are synthesized

D) mRNA attaches to ribosomes

13) Codons are part of the molecular structure of _____.

A) a protein
B) mRNA
C) tRNA

D) rRNA

14) What does it mean when we say the genetic code is redundant?
A) A single codon can specify the addition of more than one amino acid.

B) The genetic code is different for different domains of organisms.
C) The genetic code is universal (the same for all organisms).
D) More than one codon can specify the addition of the same amino acid.

15) Once researchers identified DNA as the unit of inheritance, they asked how information was transferred from the DNA in the nucleus to the site of protein synthesis in the cytoplasm. What is the mechanism of information transfer in eukarotes?
A) DNA from a single gene is replicated and transferred to the cytoplasm, where it serves as a template for protein synthesis.

B) Messenger RNA is transcribed from a single gene and transfers information from the DNA in the nucleus to the cytoplasm, where protein synthesis takes place.
C) Proteins transfer information from the nucleus to the ribosome, where protein synthesis takes place.

D) Transfer RNA takes information from DNA directly to a ribosome, where protein synthesis takes place.

16) According to the central dogma, what molecule should go in the blank? DNA → _____ → Proteins
A) mtDNA
B) rRNA

C) mRNA
D) tRNA

17) Codons are three-base sequences that specify the addition of a single amino acid. How do eukaryotic codons and prokaryotic codons compare?
A) Prokaryotic codons usually contain different bases than those of eukaryotes.
B) Prokaryotic codons usually specify different amino acids than those of eukaryotes.

C) The translation of codons is mediated by tRNAs in eukaryotes, but translation requires no intermediate molecules such as tRNAs in prokaryotes.
D) Codons are a nearly universal language among all organisms.

18) Which of the following occurs in prokaryotes but not in eukaryotes?

A) post-transcriptional splicing
B) concurrent transcription and translation
C) translation in the absence of a ribosome

D) gene regulation

19) Which of the following statements best describes the termination of transcription in prokaryotes?
A) RNA polymerase transcribes through the polyadenylation signal, causing proteins to associate with the transcript and cut it free from the polymerase.
B) RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.
C) Once transcription has initiated, RNA polymerase transcribes until it reaches the end of the chromosome.
D) RNA polymerase transcribes through a stop codon, causing the polymerase to stop advancing through the gene and release the mRNA.

20) In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein?
A) RNA polymerase I
B) RNA polymerase II

C) RNA polymerase III

D) primate

21) Transcription in eukaryotes requires which of the following in addition to RNA polymerase?

A) start and stop codons
B) ribosomes and tRNA
C) several transcription factors

D) aminoacyl-tRNA synthetase

22) Which of the following best describes the significance of the TATA box in eukaryotic promoters?
A) It is the recognition site for a specific transcription factor.
B) It sets the reading frame of the mRNA.

C) It is the recognition site for ribosomal binding.

D) Its significance has not yet been determined.

23) Which of the following does not occur in prokaryotic gene expression, but does occur in eukaryotic gene expression?
A) mRNA, tRNA, and rRNA are transcribed.
B) RNA polymerase binds to the promoter.

C) A cap is added to the 5' end of the mRNA.
D) RNA polymerase requires a primer to elongate the molecule.

24) A ribozyme is _____.
A) a catalyst that uses RNA as a substrate
B) an RNA with catalytic activity
C) an enzyme that catalyzes the association between the large and small ribosomal subunits

D) an enzyme that synthesizes RNA as part of the transcription process

25) Alternative RNA splicing _____.
A) is a mechanism for increasing the rate of translation
B) can allow the production of proteins of different sizes and functions from a single mRNA

C) can allow the production of similar proteins from different RNAs
D) increases the rate of transcription

26) In the structural organization of many eukaryotic genes, individual exons may be related to which of the following?
A) the sequence of the intron that immediately precedes each exon
B) the number of polypeptides making up the functional protein

C) the various domains of the polypeptide product

D) the number of start sites for transcription

27) In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after she has removed its 5' cap and poly-A tail. Which of the following would you expect her to find?
A) The mRNA is quickly converted into a ribosomal subunit.
B) The cell adds a new poly-A tail to the mRNA.
C) The mRNA attaches to a ribosome and is translated, but more slowly.
D) The molecule is digested by enzymes because it is not protected at the 5' end.

29) Which one of the following statements about RNA processing is true?

A) Exons are cut out before mRNA leaves the nucleus.
B) Ribozymes may function in RNA splicing.
C) RNA splicing can be catalyzed by tRNA.

D) A primary transcript is often much shorter than the final RNA molecule that leaves the nucleus.

30) A primary transcript in the nucleus of a eukaryotic cell is _____ the functional mRNA, while a primary transcript in a prokaryotic cell is _____ the functional mRNA.
A) the same size as; smaller than
B) larger than; the same size as

C) larger than; smaller than
D) the same size as; larger than

31) A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is _____.
A) TTT
B) UUA

C) UUU
D) AAA

32) Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the _____.
A) binding of ribosomes to mRNA
B) binding of the anticodon to small subunit of the ribosome

C) attachment of amino acids to rRNAs
D) binding of the anticodon to the codon and the attachment of amino acids to tRNAs

33) A mutant bacterial cell has a defective aminoacyl-tRNA synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal phenylalanine. The consequence of this for the cell will be that _____.
A) none of the proteins in the cell will contain phenylalanine

B) proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU
C) the cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine- specifying anticodons

D) the ribosome will skip a codon every time a UUU is encountered

34) There are sixty-one mRNA codons that specify an amino acid, but only forty-five tRNAs. This is best explained by the fact that _____.
A) some tRNAs have anticodons that recognize four or more different codons
B) the rules for base pairing between the third base of a codon and tRNA are flexible

C) many codons are never used, so the tRNAs that recognize them are dispensable D) the DNA codes for all sixty-one tRNAs, but some are then destroyed

35) Which of the following is the first event to take place in translation in eukaryotes? A) base pairing of activated methionine-tRNA to AUG of the messenger RNA
B) binding of the larger ribosomal subunit to smaller ribosomal subunits
C) covalent bonding between the first two amino acids

D) the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA

36) A signal peptide _____.
A) directs an mRNA molecule into the cisternal space of the ER

B) terminates translation of messenger RNA
C) helps target a protein to the ER
D) signals the initiation of transcription

37) The release factor (RF) _____.
A) binds to the stop codon in the A site in place of a tRNA
B) releases the amino acid from its tRNA to allow the amino acid to form a peptide bond C) supplies a source of energy for termination of translation
D) releases the ribosome from the ER to allow polypeptides into the cytosol

43) What must occur before a newly made polypeptide is secreted from a cell?
A) It must be translated by a ribosome that remains free within the cytosol.
B) Its signal sequence must target it to the ER, after which it goes to the Golgi.
C) Its signal sequence must be cleaved off before the polypeptide can enter the ER.
D) Its signal sequence must target it to the plasma membrane, where it causes exocytosis.

44) Translation requires _____.
A) mRNA, tRNA, DNA, and rRNA
B) mRNA, DNA, and rRNA
C) mRNA, tRNA, and rRNA
D) mRNA, tRNA, and DNA

45) During elongation, which site in the ribosome represents the location where a codon is being read?
A) E site
B) P site

C) A site
D) the small ribosomal subunit

46) Once a peptide has been formed between the amino acid attached to the tRNA in the P site and the amino acid associated with the tRNA in the A site, what occurs next?
A) translocation
B) reading of the next codon of mRNA

C) initiation
D) The codon-anticodon hydrogen bonds holding the tRNA in the A site are broken.

47) Which one of the following, if missing, would usually prevent translation from starting?

A) exon
B) 5' cap
C) AUG codon

D) poly-A tail

48) Put the following events of elongation in prokaryotic translation in chronological order. 1. Binding of mRNA with small ribosomal subunit
2. Recognition of initiation codon
3. Complementary base pairing between initiator codon and anticodon of initiator tRNA

4. Base pairing of the mRNA codon following the initiator codon with its complementary tRNA 5. Attachment of the large subunit
A) 1, 2, 3, 4, 5
B) 2, 1, 4, 3, 5

C) 5, 4, 3, 2, 1
D) 1, 2, 3, 5, 4

49) How does termination of translation take place?

A) The end of the mRNA molecule is reached.
B) A stop codon is reached.
C) The 5' cap is reached.

D) The poly-A tail is reached.

50) Post-translational modifications of proteins may include the _____.

A) removal of introns
B) addition of a 5’ cap
C) addition of a poly-A tail

D) addition of carbohydrates to form a glycoprotein

51) Which of the following statements is true about protein synthesis in prokaryotes?
A) Extensive RNA processing is required before prokaryotic transcripts can be translated.

B) Translation can begin while transcription is still in progress.
C) Prokaryotic cells have complicated mechanisms for targeting proteins to the appropriate cellular organelles.
D) Unlike eukaryotes, prokaryotes require no initiation or elongation factors.

52) Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the most serious effect on the polypeptide product? A) a deletion of a codon
B) a deletion of two nucleotides

C) a substitution of the third nucleotide in an ACC codon

D) a substitution of the first nucleotide of a GGG codon

53) A nonsense mutation in a gene _____.
A) changes an amino acid in the encoded protein
B) has no effect on the amino acid sequence of the encoded protein

C) introduces a premature stop codon into the mRNA
D) alters the reading frame of the mRNA

54) Which of the following DNA mutations is most likely to damage the protein it specifies?

A) a base-pair deletion
B) an addition of three nucleotides
C) a substitution in the last base of a codon

D) a codon deletion

55) The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in _____.
A) a base-pair substitution
B) a frameshift mutation

C) a polypeptide missing an amino acid

D) a nonsense mutation

56) Of the following, which is the most current description of a gene?
A) a unit of heredity that causes formation of a phenotypic characteristic
B) a DNA subunit that codes for a single complete protein
C) a DNA sequence that is expressed to form a functional product: either RNA or polypeptide

D) a discrete unit of hereditary information that consists of a sequence of amino acids

57) How might a single base substitution in the sequence of a gene affect the amino acid sequence of a protein encoded by the gene, and why?
A) Only a single amino acid could change, because the reading frame is unaffected.
B) The amino acid sequence would be substantially altered, because the reading frame would change with a single base substitution.

C) All amino acids following the substitution would be affected, because the reading frame would be shifted.
D) It is not possible for a single base substitution to affect protein structure, because each codon is three bases long.

58) An original section of DNA has the base sequence AGCGTTACCGT. A mutation in this DNA strand results in the base sequence AGGCGTTACCGT. This change represents _____.

A) a missense mutation
B) a point mutation

C) a silent mutation
D) frameshift mutation

59) A single base substitution mutation is least likely to be deleterious when the base change results in _____.
A) a stop codon
B) a codon that specifies the same amino acid as the original codon

C) an amino acid substitution that alters the tertiary structure of the protein

D) an amino acid substitution at the active site of an enzyme

60) Rank the following one-base point mutations (from most likely to least likely) with respect to their likelihood of affecting the structure of the corresponding polypeptide.
1. insertion mutation deep within an intron
2. substitution mutation at the third position of an exonic codon

3. substitution mutation at the second position of an exonic codon

4. deletion mutation within the first exon of the gene
A) 1, 2, 3, 4
B) 4, 3, 2, 1

C) 2, 1, 4, 3
D) 3, 1, 4, 2

1) Which of the following is a protein produced by a regulatory gene?

A) operon
B) inducer
C) promoter

D) repressor

2) A lack of which molecule would result in a cell's inability to "turn off" genes?

A) operon
B) inducer
C) promoter

D) corepressor

3) Which of the following, when taken up by a cell, binds to a repressor so that the repressor no longer binds to the operator?
A) inducer
B) promoter

C) repressor
D) corepressor

4) Most repressor proteins are allosteric. Which of the following binds with the repressor to alter its conformation?
A) inducer
B) promoter

C) transcription factor
D) cAMP

5) A mutation that inactivates a regulatory gene of a repressible operon in an E. coli cell would result in _____.
A) continuous transcription of the structural gene controlled by that regulator
B) complete inhibition of transcription of the structural gene controlled by that regulator

C) irreversible binding of the repressor to the operator
D) continuous translation of the mRNA because of alteration of its structure

6) The lactose operon is likely to be transcribed when _____.
A) there is more glucose in the cell than lactose
B) there is glucose but no lactose in the cell
C) the cyclic AMP and lactose levels are both high within the cell

D) the cAMP level is high and the lactose level is low

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7) Transcription of structural genes in an inducible operon _____.

A) occurs continuously in the cell
B) starts when the pathway's substrate is present
C) starts when the pathway's product is present

D) stops when the pathway's product is present

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8) For a repressible operon to be transcribed, which of the following must occur?
A) A corepressor must be present.
B) RNA polymerase and the active repressor must be present.
C) RNA polymerase must bind to the promoter, and the repressor must be inactive.
D) RNA polymerase must not occupy the promoter, and the repressor must be inactive.

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9) Altering patterns of gene expression in prokaryotes would most likely serve an organism's survival by _____.
A) organizing gene expression, so that genes are expressed in a given order
B) allowing each gene to be expressed an equal number of times

C) allowing an organism to adjust to changes in environmental conditions

D) allowing environmental changes to alter a prokaryote's genome

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10) In positive control of several sugar-metabolism-related operons, the catabolite activator protein (CAP) binds to DNA to stimulate transcription. What causes an increase in CAP activity in stimulating transcription?
A) an increase in glucose and an increase in cAMP
B) a decrease in glucose and an increase in cAMP
C) an increase in glucose and a decrease in cAMP
D) a decrease in glucose and a decrease in the repressor

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11) There is a mutation in the repressor that results in a molecule known as a super-repressor because it represses the lac operon permanently. Which of these would characterize such a mutant?
A) It cannot bind to the operator.

B) It cannot make a functional repressor.

C) It cannot bind to the inducer.
D) It makes a repressor that binds CAP.

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