Deck 11: DNA Biology and Technology

Question 1

For a DNA strand that is two nucleotides long, how many different sequences are possible?

A) 2
B) 4
C) 8
D) 16
E) 64 There are four possible bases that could occur in each position, so this means that there are 4², or sixteen, possible combinations of these four bases that could occur.

Answer 1

D

Question 2

If an organism's DNA contains 20% adenine nucleotides, what percentage of its DNA is composed of thymine nucleotides?

A) 10%
B) 15%
C) 20%
D) 30%
E) 40% By Chargaff's rules, A=T and G=C; thus, 20% of the DNA will consist of thymine nucleotides.

Answer 2

C

Question 3

The central dogma of molecular biology states that the information contained within genes flows in which direction?

A) DNA to DNA to protein
B) mRNA to DNA to protein
C) DNA to mRNA to protein
D) DNA to tRNA to mRNA to protein
E) DNA to rRNA to protein Information contained within genes is transcribed into mRNA. The information contained within the mRNA is then translated by a ribosome into a protein.

Answer 3

C

Question 4

During the elongation cycle of translation, the A site on a ribosome functions in

A) receiving a new tRNA with the correct amino acid.
B) holding a polypeptide as amino acids are added.
C) attaching the small subunits of rRNA to the large subunit.
D) releasing the completed polypeptide.
E) processing the rRNA. During the elongation cycle, an incoming tRNA carrying the specified amino acid binds to the anticodon of the mRNA at the A site of the ribosome.

Question 5

For a DNA strand that contains the sequence AGT in the 5' to 3' direction, what nucleotides are found on the other DNA strand in the 5' to 3' direction?

A) ACT
B) TGA
C) AGT
D) TCA
E) GTA By Chargaff's rules, T hydrogen bonds with A, C with G, and A with T. Since the opposite strand runs antiparallel, the correct order of these nucleotides is ACT.

Question 6

The genetic code in bacteria is different than the genetic code in animals and plants.

Question 7

tRNAs carrying the correct amino acid recognize the proper codons on the mRNA because

A) the anticodon of the tRNA hydrogen binds to the codon of the mRNA by complementary base pairing.
B) the codon of the tRNA binds to the anticodon of the ribosome by complementary base pairing.
C) the anticodon of the tRNA carries the correct amino acid.
D) the amino acid binds to the anticodon of the mRNA and brings the correct tRNA with it.
E) the codon of the mRNA binds the correct amino acid, and the tRNA stabilizes this interaction. The anticodon of the tRNA binds to the codon of the mRNA by complementary base pairing. The tRNA carries the encoded amino acid.

Question 8

A defect in DNA ligase would most likely cause

A) normal replication, but gaps remain in the sugar-phosphate DNA backbone.
B) failure to remove introns from the primary mRNA.
C) incompletely processed primary mRNA that does not get translated properly.
D) translation to initiate normally but fail to proceed to elongation.
E) DNA strands to separate normally but fail to join nucleotides in the growing nucleotide chain. DNA ligase is needed during DNA replication to seal breaks in the sugar-phosphate backbone after DNA polymerase joins nucleotides into a new chain. If it is defective, all other processes may occur normally, but there will be gaps remaining in the sugar-phosphate DNA backbone when DNA replication occurs.

Question 9

The three steps that are required for DNA replication are

A) unwinding, complementary base pairing, and joining.
B) base doubling, unwinding, and joining.
C) complementary base pairing, transcription, and translation.
D) unwinding, transcription, and translation.
E) unwinding, base doubling, and base pairing. In DNA replication, the DNA is first unwound by helicase. Then, new complementary nucleotides are positioned by complementary base pairing to each strand. The new nucleotides are then joined into a new strand.

Question 10

If an organism's DNA contains 17% adenine nucleotides and 33% guanine nucleotides, what percentage of its DNA is composed of cytosine nucleotides?

A) 8.5%
B) 17%
C) 25%
D) 33%
E) 50% By Chargaff's rules, the amount of G=C, so the DNA is also 33% cytosine.

Question 11

This figure represents

A) replication.
B) translation.
C) transcription.
D) transformation.
E) base pairing.

Question 12

RNA differs from DNA because RNA

A) is double-stranded, whereas DNA is not.
B) may double back and base pair with itself, whereas DNA does not.
C) is never single-stranded, whereas DNA may or may not be.
D) can self-replicate, whereas DNA replication requires enzymes.
E) is replicated along with DNA but does not require strand separation like DNA does.

Question 13

The X-ray diffraction pattern of DNA discovered by Rosalind Franklin showed that DNA

A) is helical.
B) has a repeated pattern.
C) is both helical and has a repeated pattern.
D) contains beta sheets arranged in a repeated pattern.
E) contains alpha helices and beta sheets. Rosalind Franklin's DNA diffraction data demonstrated that it is helical, from the X pattern in the center, and that it is repeated over and over, from the dark portions at the top and bottom edges. James Watson and Francis Crick incorporated Franklin and Chargaff's work into their description of the structure of DNA.

Question 14

For a DNA strand composed of the sequence AGT in the 5' to 3' direction, the free phosphate is on the ________ nucleotide and the free hydroxyl is on the ________ nucleotide.

A) T; A
B) A; G
C) A; A
D) G; T
E) A; T By convention, DNA sequences are written 5' to 3' from left to right. The free phosphate is thus found on the adenine nucleotide, and the free hydroxyl is found on the thymine nucleotide.

Question 15

DNA replication is called semiconservative because

A) one of the two resulting DNA molecules is new.
B) the two resulting DNA molecules each have one new DNA strand and one old strand from the original DNA molecule.
C) both of the resulting DNA molecules are composed of new strands of nucleotides.
D) no extra nucleotides are incorporated into the replicated DNA molecules.
E) the sequence of nucleotides in one strand is conserved, whereas the new DNA molecule consists of a unique sequence of nucleotides. At the end of replication, each new DNA molecule contains one old DNA strand and one new DNA strand. The old strand was used as a template to build the new strand.

Question 16

mRNA must be processed in the cytoplasm before being used in protein synthesis.

Question 17

Which base is found in DNA, but not in RNA?

A) cytosine
B) uracil
C) thymine
D) adenine
E) guanine In RNA, uracil replaces thymine.

Question 18

If an organism's DNA contains 20% adenine nucleotides, what percentage of its DNA is composed of guanine nucleotides?

A) 10%
B) 15%
C) 20%
D) 30%
E) 40% Since 20% of the organism's DNA consists of adenine nucleotides, 20% consists of thymine nucleotides. The other 60% consists of guanine and cytosine. Since the amount of G=C, the DNA is 30% guanine and 30% cytosine.

Question 19

Which of the following enzymes is needed to reseal breaks in the sugar-phosphate backbone during replication?

A) DNA polymerase
B) RNA polymerase
C) RNA ligase
D) helicase
E) DNA ligase DNA ligase reseals breaks in the sugar-phosphate backbone of DNA.

Question 20

What chemical force must be overcome in order to separate the two DNA strands during replication?

A) hydrophobic interactions
B) intrastrand folding
C) ionic bonds
D) phosphodiester bonds
E) hydrogen bonds DNA helicase helps to disrupt the hydrogen bonds between base pairs that hold the two strands together.

Question 21

The protein derived from a particular gene is different when it is found in a neuron than in a muscle cell. This is most likely due to

A) alternative mRNA processing.
B) regulation of mRNA translation.
C) alteration of protein activity.
D) mRNA editing.
E) DNA excision. Exon inclusion or exclusion, or intron inclusion, as a result of alternative mRNA processing may yield different mRNA transcripts from the same gene, giving rise to multiple proteins from the same gene.

Question 22

Which process requires the participation of all three types of RNA?

A) transcription
B) translation
C) RNA processing
D) replication
E) complementary base pairing During translation, an mRNA is translated by a ribosome, which contains rRNA, and tRNA brings the specified amino acids to the ribosome.

Question 23

Using three bases to represent each amino acid in a polypeptide

A) ensures that all amino acids are represented at least once by the code.
B) ensures that other organisms can read the code too.
C) ensures that DNA can replicate properly.
D) prevents the wrong amino acid from being incorporated into a protein.
E) prevents early termination of transcription.

Question 24

The information contained within a gene is not directly copied into which of the following chemical forms?

A) tRNA, rRNA
B) mRNA, tRNA
C) rRNA, protein
D) mRNA, protein
E) tRNA, protein The information contained within a gene is transcribed into mRNA, and then into a protein. The other forms of RNA, tRNA, and rRNA, are necessary for the process of translation.

Question 25

Which of the DNA sequences shown in the figure is/are bound by a regulatory protein?

A) 1
B) 2
C) 3
D) 1 and 4
E) 2 and 3

Question 26

The stages of translation are

A) transcription, mRNA processing, and termination.
B) DNA replication, transcription, and termination.
C) initiation, transcription, elongation cycle, and termination.
D) initiation, elongation cycle, and termination.
E) initiation, transcription, mRNA processing, and termination.

Question 27

Prokaryotes cannot regulate gene expression at which of the following levels?

A) mRNA transcription and mRNA translation
B) mRNA translation
C) alternative mRNA processing and chromatin compaction
D) mRNA translation and longevity of mRNA
E) mRNA transcription and longevity of mRNA

Question 28

Which of the following events in gene expression control does not occur in the nucleus?

A) chromatin condensation
B) mRNA translation
C) DNA transcription
D) mRNA processing
E) transcription factor binding

Question 29

Which of the following allows a cell to decipher the genetic code?

A) rRNA
B) tRNA
C) mRNA
D) DNA
E) protein In translation, the anticodon of a tRNA carrying an amino acid hydrogen bonds with the codon on the mRNA. Thus, tRNA acts as an adaptor to enable the cell to read the genetic code contained within the mRNA.

Question 30

Which of the following processes does not occur within the nucleus?

A) DNA replication
B) transcription
C) intron removal
D) translation
E) primary mRNA splicing Translation occurs on ribosomes within the cytoplasm, or at the membrane of the rough endoplasmic reticulum.

Question 31

Heterochromatin differs from euchromatin in that heterochromatin

A) is transcriptionally active, whereas euchromatin is not.
B) is not found in Barr bodies.
C) is transcriptionally inactive.
D) is the result of the unpacking of euchromatin.
E) contains DNA with accessible promoters. Heterochromatin is highly condensed chromatin that is transcriptionally inactive, because promoters are inaccessible to RNA polymerase. When it is unpacked, it becomes euchromatin.

Question 32

What would be the most likely result on the regulation of the lac operon from a nonfunctional repressor protein?

A) transcription of the lactose metabolizing genes, even when lactose is absent
B) no transcription of the lactose metabolizing genes, even when lactose is present
C) binding of the repressor protein to the operator, even when lactose is present
D) binding of the repressor protein to the regulatory gene in both the presence and absence of lactose
E) no transcription of the regulatory gene, even in the presence of lactose

Question 33

DNA replication makes an) ________ copy of the DNA strand, while transcription makes an) ________ copy of the DNA strand.

A) mRNA; DNA
B) DNA; mRNA
C) DNA; tRNA
D) mRNA; tRNA
E) mRNA; rRNA Transcription and DNA replication are separate processes. Transcription transfers the information contained within DNA into an mRNA, while DNA replication simply copies the information into another DNA molecule.

Question 34

The two DNA strands must be separated before DNA replication or transcription can occur.

Question 35

A point mutation in the operator of the lac operon would most likely cause

A) no transcription of the lactose metabolizing genes, even when lactose is absent.
B) no transcription of the lactose metabolizing genes, even when lactose is present.
C) no binding of the repressor protein to the operator, even when lactose is absent.
D) binding of the repressor protein to the regulatory gene in both the presence and absence of lactose.
E) no transcription of the regulatory gene, even in the presence of lactose. The repressor binds the operator when lactose is absent. Like a faulty repressor, a mutation in the operator would likely cause the repressor not to bind the operator, regardless of whether lactose is present.

Question 36

Failure to remove introns from a primary mRNA would most likely cause

A) irregularities in transcription.
B) abnormal translation.
C) DNA to mutate.
D) DNA replication to fail.
E) transcription to terminate early. The exons of a eukaryotic primary mRNA contain the protein coding region of the gene, and thus the introns must be removed during primary mRNA splicing so that a usable message is obtained. If they are not removed, the protein that would result from translating the mRNA will be altered.

Question 37

The unpacking of heterochromatin into euchromatin does not immediately result in DNA transcription because

A) Barr bodies are still present.
B) histones still block the binding of RNA polymerase to the promoter.
C) euchromatin is always transcriptionally inactive.
D) transcription factors still block the binding of RNA polymerase to the promoter.
E) heterochromatin contains DNA with accessible promoters. Even euchromatin is inaccessible unless the nucleosomes are moved to make the promoter accessible to RNA polymerase.

Question 38

The sequence of the peptide that would result from transcribing and translating the gene pictured would be

A) Tyr-Ala-Asn.
B) Ile-Ser-Val.
C) no peptide would be made; the first codon means "stop."
D) Met-Arg-Leu.
E) Tyr-Ser-Val.

Question 39

Transcription activators are different from transcription factors in that

A) transcription activators are required for RNA polymerase binding, while transcription factors slow RNA polymerase binding.
B) transcription activators accelerate transcription, while transcription factors assist RNA polymerase binding.
C) transcription activators slow transcription, while transcription factors accelerate transcription.
D) transcription factors prevent RNA polymerase binding, while transcription activators assist RNA polymerase binding.
E) transcription factors are required for RNA polymerase binding, while transcription activators accelerate transcription. Transcription factors are proteins that are required for RNA polymerase to bind to a promoter. RNA polymerase can bind a promoter and transcribe a gene when transcription activators are not present, but their presence accelerates the process when they bind DNA and promote transcription.

Question 40

If RNA polymerase malfunctions,

A) one of the subunits of rRNA will not be transcribed from DNA.
B) amino acids will not be joined to their tRNA.
C) mRNA cannot bind to rRNA.
D) an mRNA will not be formed.
E) mRNA cannot copy itself. RNA polymerase makes an mRNA transcript of the gene being transcribed. If RNA polymerase malfunctions, the mRNA is not made.

Question 41

Female mammals form Barr bodies because

A) compacting the chromatin of one of their X chromosomes allows them to inactivate it and produce the same amount of gene product as a male.
B) unpacking one of their X chromosomes allows them to produce more gene product than a male.
C) compacting the chromatin in one of their X chromosomes allows them to conserve histone proteins.
D) compacting the chromatin in one of their X chromosomes allows them to produce more gene product than a male from the other X chromosome.
E) unpacking one of their X chromosomes allows them to choose which allele they wish to express, which a male cannot do. Barr bodies are formed because otherwise, a female would produce twice as much gene product as a male from genes on the X chromosome, and too much of some gene products can be harmful.

Question 42

Prokaryotes regulate gene expression with a promoter.

Question 43

What is the hereditary material found in all cells?

A) DNA
B) rRNA
C) mRNA
D) tRNA
E) ATP While mRNA, tRNA, and rRNA are all necessary to express the genetic code of an organism, it is DNA that carries the information to make the other molecules and to make the proteins that carry out the necessary functions of the cell.

Question 44

In eukaryotes, one gene may specify the construction of several proteins.

Question 45

Which of the following series of events are in the correct order?

A) chemical binds to receptor, signal transduction pathway stimulates transcription activator, target gene is transcribed and translated
B) signal transduction pathway stimulates receptor, transcription activator is activated by target gene
C) chemical binds to receptor, target gene is transcribed and translated, signal transduction pathway stimulates proteins that bring about desired changes
D) signal transduction pathway activates receptor, chemical binds to receptor, target gene stimulates transcription activator
E) chemical binds to receptor, signal transduction pathway stimulates target gene, target gene stimulates transcription activator Signal transduction pathways are initiated by the binding of a chemical signal by a receptor, which initiates the pathway. The pathway usually ends with the stimulation of a transcription activator, which brings about the needed response in the cell by causing the transcription of needed genes.

Question 46

An intervening sequence of DNA that is not expressed is called an)

A) intron.
B) exon.
C) gene.
D) replicon.
E) promoter. During mRNA processing, segments of the mRNA that do not code for an amino acid necessary for the protein are removed. These noncoding sequences that interrupt the "message" of the mRNA are called introns.

Question 47

Histone displacement is necessary for transcription to occur in euchromatin.

Question 48

Proteins are active immediately after translation occurs.

Question 49

Which section of the DNA is inactive?

A) heterochromatin
B) intron
C) exon
D) euchromatin
E) nucleosome

Question 50

If the maternal X chromosome is inactive and becomes the Barr body in one cell, then the maternal X chromosome becomes the Barr body in every cell of that woman's body.

Question 51

Signal transduction pathways can stimulate transcription activators.