GenBio 1- Exam 3
47) In an experiment, DNA is allowed to replicate in an environment with all necessary enzymes, dATP, dCTP, dGTP, and radioactively labeled dTTP (³H thymidine) for several minutes and then switched to nonradioactive medium. It is then viewed by electron microscopy and autoradiography. The figure above represents the results. Which of the following is the most likely interpretation? A) There are two replication forks going in opposite directions. B) Thymidine is only being added where the DNA strands are furthest apart. C) Thymidine is only added at the very beginning of replication. D) Replication proceeds in one direction only.
A) There are two replication forks going in opposite directions.
Given a population that contains genetic variation, what is the correct sequence of the following events, under the influence of natural selection? 1. Well-adapted individuals leave more offspring than do poorly adapted individuals. 2. A change occurs in the environment. 3. Genetic frequencies within the population change. 4. Poorly adapted individuals have decreased survivorship.
2,4,1,3
During elongation, which site in the ribosome represents the location where a codon is being read?
A site
Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine? A) 8% B) 16% C) 31% D) 42% E) It cannot be determined from the information provided.
A) 8%
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) All organisms have experienced convergent evolution. C) DNA was the first genetic material. D) The same codons in different organisms translate into the different amino acids. E) Different organisms have different numbers of different types of amino acids.
A) A gene from an organism can theoretically be expressed by any other organism.
The "universal" genetic code is now known to have exceptions. Evidence for this can be found if which of the following is true? A) If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only). B) If one stop codon, such as UGA, is found to have a different effect on translation than another stop codon, such as UAA. C) If prokaryotic organisms are able to translate a eukaryotic mRNA and produce the same polypeptide. D) If several codons are found to translate to the same amino acid, such as serine. E) If a single mRNA molecule is found to translate to more than one polypeptide when there are two or more AUG sites.
A) If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only).
A mutation that inactivates the 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) inactivation of RNA polymerase by alteration of its active site. E) continuous translation of the mRNA because of alteration of its structure.
A) continuous transcription of the structural gene controlled by that regulator.
Most repressor proteins are allosteric. Which of the following binds with the repressor to alter its conformation? A) inducer B) promoter C) RNA polymerase D) transcription factor E) cAMP
A) inducer
he spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage? A) nuclease, DNA polymerase, DNA ligase B) telomerase, primase, DNA polymerase C) telomerase, helicase, single-strand binding protein D) DNA ligase, replication fork proteins, adenylyl cyclase E) nuclease, telomerase, primase
A) nuclease, DNA polymerase, DNA ligase
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 E) different five-carbon sugars
A) sequence of bases
Which of the following can be determined directly from X-ray diffraction photographs of crystallized DNA? A) the diameter of the helix B) the rate of replication C) the sequence of nucleotides D) the bond angles of the subunits E) the frequency of A vs. T nucleotides
A) the diameter of the helix
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.
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.
The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that A) the nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose. B) the nucleoside triphosphates have two phosphate groups; ATP has three phosphate groups. C) ATP contains three high-energy bonds; the nucleoside triphosphates have two. D) ATP is found only in human cells; the nucleoside triphosphates are found in all animal and plant cells. E) triphosphate monomers are active in the nucleoside triphosphates, but not in ATP.
A) the nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose.
The TATA sequence is found only several nucleotides away from the start site of transcription. This most probably relates to which of the following? A) the number of hydrogen bonds between A and T in DNA B) the triplet nature of the codon C) the ability of this sequence to bind to the start site D) the supercoiling of the DNA near the start site E) the 3-D shape of a DNA molecule
A) the number of hydrogen bonds between A and T in DNA
Which of the following variations on translation would be most disadvantageous for a cell? A) translating polypeptides directly from DNA B) using fewer kinds of tRNA C) having only one stop codon D) lengthening the half-life of mRNA E) having a second codon (besides AUG) as a start codon
A) translating polypeptides directly from DNA
Which of the following statements about the DNA in one of your brain cells is true? A. It is the same as the DNA in one of your heart cells. B. Many genes are grouped into operon-like clusters. C. The majority of genes are likely to be transcribed. D. Most of the DNA codes for protein. E. Each gene lies immediately adjacent to an enhancer.
A. It is the same as the DNA in one of your heart cells.
The nitrogenous base adenine is found in all members of which group?
ATP, RNA, and DNA
Which one of the following, if missing, would usually prevent translation from starting?
AUG codon
How many unique gametes could be produced through independent assortment by an individual with the genotype AaBbCCDdEE? A) 4 B) 8 C) 16 D) 32 E) 64
B) 8
Allolactose, an isomer of lactose, is formed in small amounts from lactose. An E. coli cell is presented for the first time with the sugar lactose (containing allolactose) as a potential food source. Which of the following occurs when the lactose enters the cell? A) The repressor protein attaches to the regulator. B) Allolactose binds to the repressor protein. C) Allolactose binds to the regulator gene. D) The repressor protein and allolactose bind to RNA polymerase. E) RNA polymerase attaches to the regulator.
B) Allolactose binds to the repressor protein.
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. E) The mass of histone in chromatin is approximately nine times the mass of DNA.
B) Histone H1 is not present in the nucleosome bead; instead, it draws the nucleosomes together.
Which of the following is a function of a poly-A signal sequence? A) It adds the poly-A tail to the 3' end of the mRNA. B) It codes for a sequence in eukaryotic transcripts that signals enzymatic cleavage ~1035 nucleotides away. C) It allows the 3' end of the mRNA to attach to the ribosome. D) It is a sequence that codes for the hydrolysis of the RNA polymerase. E) It adds a 7-methylguanosine cap to the 3' end of the mRNA.
B) It codes for a sequence in eukaryotic transcripts that signals enzymatic cleavage ~1035 nucleotides away.
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) No proofreading will occur. B) No replication fork will be formed. C) The DNA will supercoil. D) Replication will occur via RNA polymerase alone. E) Replication will require a DNA template from another source.
B) No replication fork will be formed.
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) Radioactive thymine would pair with nonradioactive guanine. E) DNA in both daughter cells would be radioactive.
E) DNA in both daughter cells would be radioactive.
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) Okazaki fragments prevent elongation in the 3' to 5' direction. C) the polarity of the DNA molecule prevents addition of nucleotides at the 3' end. D) replication must progress toward the replication fork. E) DNA polymerase can only add nucleotides to the free 3' end.
E) DNA polymerase can only add nucleotides to the free 3' end.
The role of a metabolite that controls a repressible operon is to A) bind to the promoter region and decrease the affinity of RNA polymerase for the promoter. B) bind to the operator region and block the attachment of RNA polymerase to the promoter. C) increase the production of inactive repressor proteins. D) bind to the repressor protein and inactivate it. E) bind to the repressor protein and activate it.
E) bind to the repressor protein and activate it.
A lack of which molecule would result in the cell's inability to "turn off" genes? A) operon B) inducer C) promoter D) ubiquitin E) corepressor
E) corepressor
To repair a thymine dimer by nucleotide excision repair, in which order do the necessary enzymes act? A) exonuclease, DNA polymerase III, RNA primase B) helicase, DNA polymerase I, DNA ligase C) DNA ligase, nuclease, helicase D) DNA polymerase I, DNA polymerase III, DNA ligase E) endonuclease, DNA polymerase I, DNA ligase
E) endonuclease, DNA polymerase I, DNA ligase
The DNA of telomeres has been found to be highly conserved throughout the evolution of eukaryotes. What does this most probably reflect? A) the inactivity of this DNA B) the low frequency of mutations occurring in this DNA C) that new evolution of telomeres continues D) that mutations in telomeres are relatively advantageous E) that the critical function of telomeres must be maintained
E) that the critical function of telomeres must be maintained
The tryptophan operon is a repressible operon that is A) permanently turned on. B) turned on only when tryptophan is present in the growth medium. C) turned off only when glucose is present in the growth medium. D) turned on only when glucose is present in the growth medium. E) turned off whenever tryptophan is added to the growth medium.
E) turned off whenever tryptophan is added to the growth medium.
A particular triplet of bases in a the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is
E. 3' UCA 5'.
Gene expression might be altered at the level of post-transcriptional processing in eukaryotes rather than prokaryotes because of which of the following?
Eukaryotic exons may be spliced in alternative patterns.
Use the following choices for the following questions: I. helicase II. DNA polymerase III III. ligase IV. DNA polymerase I V. primase Which of the enzymes separates the DNA strands during replication?
I. helicase II
Use the following choices for the following questions: I. helicase II. DNA polymerase III III. ligase IV. DNA polymerase I V. primase Which of the enzymes covalently connects segments of DNA?
III. ligase
Use the following choices for the following questions: I. helicase II. DNA polymerase III III. ligase IV. DNA polymerase I V. primase Which of the enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments?
IV. DNA polymerase
Which of the following statements describes the eukaryotic chromosome?
It consists of a single linear molecule of double stranded DNA plus proteins.
In the process of transcription, ___________________.
RNA is synthesized
Within six months of effectively using methicillin to treat S. aureus infections in a community, all new infections were caused by MRSA. How can this result be explained?
Some drug-resistant bacteria were present at the start of treatment, and natural selection increased their frequency.
What is meant by the description "antiparallel" regarding the strands that make up DNA?
The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.
Over evolutionary time, many cave-dwelling organisms have lost their eyes. Tapeworms have lost their digestive systems. Whales have lost their hind limbs. How can natural selection account for these losses?
Under particular circumstances that persisted for long periods, each of these structures presented greater costs than benefits.
Use the following choices for the following questions: I. helicase II. DNA polymerase III III. ligase IV. DNA polymerase I V. primase Which of the enzymes synthesizes short segments of RNA?
V. primase
How does termination of translation take place?
a stop codon is reached
Three populations of crickets look very similar, but the males have courtship songs that sound different. What function would this difference in song likely serve if the populations came in contact?
behavioral reproductive isolating mechanism
In eukaryotes, general transcription factors ______________.
bind to other proteins or to the TATA box
What would occur if the repressor of an inducible operon were mutated so that it could not bind to the operator?
continuous transcription of the operon's genes
Which of the following is the best modern definition of evolution?
descent with modification
In seedcracker finches from Cameroon, small and large billed birds specialize in cracking soft and hard seeds, respectively. If long-term climatic change resulted in a all seeds becoming hard, what type of selection would then operate on the finch population?
directional selection
An enhancer is located _______________ to the promoter.
distal
DNA methylation and histone acetylation are examples of _____________________.
epigenetic phenomena
Rocky Mountain juniper (Juniperus scopulorum) and one-seeded juniper (J. monosperma) have overlapping ranges. Pollen grains (which contain sperm cells) from one speicies are unable to germinate and make pollen tubes on female ovules (which contain egg cells) of the other species. These two juniper species are kept separate by _______________.
gametic isolation
Which of the following must exist in a population before natural selection can act upon that population?
genetic variation among individuals
In a nucleosome, the DNA is wrapped around
histones
In modern terminology, diversity is understood to be a result of genetic variation. Which of the following is a recognized source of variation for evolution?
recombination by crossing over in meiosis
Two species of frogs belonging to the same genus occasionally mate, but the embryos stop developing after a day and then die. These two frog species separate by _____________.
reduced hybrid viability
What is the function of topoisomerase?
relieving strain in the DNA ahead of the replication fork
If a particular operon encodes enzymes for making an essential amino acid and is regulated like the lac operon, then _____________________________________.
the amino acid acts as a corepressor
The lactose operon is likely to be transcribed when _____________.
the cyclic AMP and lactose levels are both high within the cell
The leading and lagging strands differ in that
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.
Which of the following is directly related to a single amino acid?
the three-base sequence of mRNA
The functioning of enhancers is an example of _______________________.
transcriptional control of gene expression
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. E) Prokaryotes have telomeres, and eukaryotes do not.
B) Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.
An Okazaki fragment has which of the following arrangements? A) primase, polymerase, ligase B) 3' RNA nucleotides, DNA nucleotides 5' C) 5' RNA nucleotides, DNA nucleotides 3' D) DNA polymerase I, DNA polymerase III E) 5' DNA to 3'
C) 5' RNA nucleotides, DNA nucleotides 3'
In an analysis of the nucleotide composition of DNA, which of the following will be found? A) A = C B) A = G and C = T C) A + C = G + T D) G + C = T + A
C) A + C = G + T
t a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork: 3' C C T A G G C T G C A A T C C 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' G C C T A G G 3' B) 3' G C C T A G G 5' C) 5' A C G T T A G G 3' D) 5' A C G U U A G G 3' E) 5' G C C U A G G 3'
D) 5' A C G U U A G G 3'
Which of the following provides some evidence that RNA probably evolved before DNA? A) RNA polymerase uses DNA as a template. B) RNA polymerase makes a single-stranded molecule. C) RNA polymerase does not require localized unwinding of the DNA. D) DNA polymerase uses primer, usually made of RNA. E) DNA polymerase has proofreading function.
D) DNA polymerase uses primer, usually made of RNA.
Which of the following statements describes the eukaryotic chromosome? A) It is composed of DNA alone. B) The nucleosome is its most basic functional subunit. C) The number of genes on each chromosome is different in different cell types of an organism. D) It consists of a single linear molecule of double-stranded DNA plus proteins. E) Active transcription occurs on heterochromatin but not euchromatin.
D) It consists of a single linear molecule of double-stranded DNA plus proteins.
Why did the F₁ offspring of Mendel's classic pea cross always look like one of the two parental varieties? A) No genes interacted to produce the parental phenotype. B) Each allele affected phenotypic expression. C) The traits blended together during fertilization. D) One phenotype was completely dominant over another. E) Different genes interacted to produce the parental phenotype.
D) One phenotype was completely dominant over another.
Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. This occurs because their cells are impaired in what way? A) They cannot replicate DNA. B) They cannot undergo mitosis. C) They cannot exchange DNA with other cells. D) They cannot repair thymine dimers. E) They do not recombine homologous chromosomes during meiosis.
D) They cannot repair thymine dimers.
Duchenne muscular dystrophy (DMD) is caused by a gene on the human X chromosome. The patients have muscles that weaken over time because they have absent or decreased dystrophin, a muscle protein. They rarely live past their 20s. How likely is it for a woman to have this condition? A) Women can never have this condition. B) One-half of the daughters of an affected man could have this condition. C) One-fourth of the children of an affected father and a carrier mother could have this condition. D) Very rarely would a woman have this condition; the condition would be due to a chromosome error. E) Only if a woman is XXX could she have this condition.
D) Very rarely would a woman have this condition; the condition would be due to a chromosome error.
Which of the following would you expect of a eukaryote lacking telomerase? A) a high probability of somatic cells becoming cancerous B) production of Okazaki fragments C) inability to repair thymine dimers D) a reduction in chromosome length in gametes E) high sensitivity to sunlight
D) a reduction in chromosome length in gametes
Which of the following nucleotide triplets best represents a codon? A) a triplet separated spatially from other triplets B) a triplet that has no corresponding amino acid C) a triplet at the opposite end of tRNA from the attachment site of the amino acid D) a triplet in the same reading frame as an upstream AUG E) a sequence in tRNA at the 3' end
D) a triplet in the same reading frame as an upstream AUG
The enzyme telomerase solves the problem of replication at the ends of linear chromosomes by which method? A) adding a single 5' cap structure that resists degradation by nucleases B) causing specific double-strand DNA breaks that result in blunt ends on both strands C) causing linear ends of the newly replicated DNA to circularize D) adding numerous short DNA sequences such as TTAGGG, which form a hairpin turn E) adding numerous GC pairs which resist hydrolysis and maintain chromosome integrity
D) adding numerous short DNA sequences such as TTAGGG, which form a hairpin turn
Which of the following is a protein produced by a regulatory gene? A) operon B) inducer C) promoter D) repressor E) corepressor
D) repressor
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 binding proteins E) exonuclease
D) single-strand binding proteins
In a linear eukaryotic chromatin sample, which of the following strands is looped into domains by scaffolding? A) DNA without attached histones B) DNA with H1 only C) the 10-nm chromatin fiber D) the 30-nm chromatin fiber E) the metaphase chromosome
D) the 30-nm chromatin fiber
The lactose operon is likely to be transcribed when A) there is more glucose in the cell than lactose. B) the cyclic AMP levels are low. C) there is glucose but no lactose in the cell. D) the cyclic AMP and lactose levels are both high within the cell. E) the cAMP level is high and the lactose level is low.
D) the cyclic AMP and lactose levels are both high within the cell.
Which of the following does not occur in prokaryotic gene expression, but does occur in eukaryotic gene expression? A. RNA polymerase binds to the promoter. B. RNA polymerase requires a primer to elongate the molecule. C. mRNA, tRNA, and rRNA are transcribed. D. A cap is added to the 5' end of the mRNA.
D. A cap is added to the 5' end of the mRNA.
Two potential devices that eukaryotic cells use to regulate transcription are
DNA methylation and histone modification.
Which enzyme catalyzes the elongation of a DNA strand in the 5' to 3' direction?
DNA polymerase III
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) RNA polymerase transcribes through an intron, and the snRNPs cause the polymerase to let go of the transcript. D) Once transcription has initiated, RNA polymerase transcribes until it reaches the end of the chromosome. E) RNA polymerase transcribes through a stop codon, causing the polymerase to stop advancing through the gene and release the mRNA.
B) RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.
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. E) Pseudogenes would be transcribed to compensate for the decreased protein in the cell.
B) The cell's DNA couldn't be packed into its nucleus
Studies of nucleosomes have shown that histones (except H1) exist in each nucleosome as two kinds of tetramers: one of 2 H2A molecules and 2 H2B molecules, and the other as 2 H3 and 2 H4 molecules. Which of the following is supported by this data? A) DNA can wind itself around either of the two kinds of tetramers. B) The two types of tetramers associate to form an octamer. C) DNA has to associate with individual histones before they form tetramers. D) Only H2A can form associations with DNA molecules. E) The structure of H3 and H4 molecules is not basic like that of the other histones.
B) The two types of tetramers associate to form an octamer.
In response to chemical signals, prokaryotes can do which of the following? A) turn off translation of their mRNA B) alter the level of production of various enzymes C) increase the number and responsiveness of their ribosomes D) inactivate their mRNA molecules E) alter the sequence of amino acids in certain proteins
B) alter the level of production of various enzymes
What is a ribozyme? A) an enzyme that uses RNA as a substrate B) an RNA with enzymatic 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 E) an enzyme that synthesizes RNA primers during DNA replication
B) an RNA with enzymatic activity
Alternative RNA splicing A) is a mechanism for increasing the rate of transcription. B) can allow the production of proteins of different sizes from a single mRNA. C) can allow the production of similar proteins from different RNAs. D) increases the rate of transcription. E) is due to the presence or absence of particular snRNPs.
B) can allow the production of proteins of different sizes from a single mRNA.
Which of the following, when taken up by the cell, binds to the repressor so that the repressor no longer binds to the operator? A) ubiquitin B) inducer C) promoter D) repressor E) corepressor
B) inducer
Polytene chromosomes of Drosophila salivary glands each consist of multiple identical DNA strands that are aligned in parallel arrays. How could these arise? A) replication followed by mitosis B) replication without separation C) meiosis followed by mitosis D) fertilization by multiple sperm E) special association with histone proteins
B) replication without separation
Transcription of the 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. E) does not result in the production of enzymes.
B) starts when the pathway's substrate is present.
What do we mean when we use the terms monohybrid cross and dihybrid cross? A) A monohybrid cross involves a single parent, whereas a dihybrid cross involves two parents. B) A monohybrid cross produces a single progeny, whereas a dihybrid cross produces two progeny. C) A dihybrid cross involves organisms that are heterozygous for two characters and a monohybrid cross involves only one. D) A monohybrid cross is performed for one generation, whereas a dihybrid cross is performed for two generations. E) A monohybrid cross results in a 9:3:3:1 ratio whereas a dihybrid cross gives a 3:1 ratio.
C) A dihybrid cross involves organisms that are heterozygous for two characters and a monohybrid cross involves only one.
A part of the promoter, called the TATA box, is said to be highly conserved in evolution. Which of the following might this illustrate? A) The sequence evolves very rapidly. B) The sequence does not mutate. C) Any mutation in the sequence is selected against. D) The sequence is found in many but not all promoters. E) The sequence is transcribed at the start of every gene.
C) Any mutation in the sequence is selected against.
Which enzyme catalyzes the elongation of a DNA strand in the 5' → 3' direction? A) primase B) DNA ligase C) DNA polymerase III D) topoisomerase E) helicase
C) DNA polymerase III
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 catalyzes the lengthening of telomeres. C) It joins Okazaki fragments together. D) It unwinds the parental double helix. E) It stabilizes the unwound parental DNA.
C) It joins Okazaki fragments together.
During splicing, which molecular component of the spliceosome catalyzes the excision reaction? A) protein B) DNA C) RNA D) lipid E) sugar
C) RNA
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 cannot be present, and the repressor must be inactive. E) RNA polymerase must not occupy the promoter, and the repressor must be inactive.
C) RNA polymerase must bind to the promoter, and the repressor must be inactive.
Altering patterns of gene expression in prokaryotes would most likely serve the organism's survival in which of the following ways? 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 the organism to adjust to changes in environmental conditions D) allowing young organisms to respond differently from more mature organisms E) allowing environmental changes to alter the prokaryote's genome
C) allowing the organism to adjust to changes in environmental conditions
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 5' 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 E) the "no ends" of a circular chromosome
C) gaps left at the 5' end of the lagging strand
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 restriction enzyme cutting sites E) the number of start sites for transcription
C) the various domains of the polypeptide product
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 E) to rejoin the two DNA strands (one new and one old) after replication
C) to add nucleotides to the 3' end of a growing DNA strand
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. Unlike eukaryotes, prokaryotes require no initiation or elongation factors. C. Translation can begin while transcription is still in progress. D. Prokaryotic cells have complicated mechanisms for targeting proteins to the appropriate cellular organelles.
C. Translation can begin while transcription is still in progress.
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 substitution of the third nucleotide in an ACC codon B. an insertion of a codon C. a deletion of two nucleotides D. a substitution of the first nucleotide of a GGG codon E. a deletion of a codon
C. a deletion of two nucleotides
