Bio chapter 13

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? ANSWER: 8% 16% 31% 42%

A

A new DNA strand elongates only in the 5' to 3' direction because ANSWER: DNA polymerase begins adding nucleotides at the 5' end of the template. DNA polymerase can only add nucleotides to the free 3' end. Okazaki fragments prevent elongation in the 3' to 5' direction. replication must progress toward the replication fork.

B

During DNA replication, which of the following enzymes covalently connects segments of DNA? ANSWER: helicase DNA polymerase III ligase DNA polymerase I primase

C

In DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine. Which of the following investigators was (were) responsible for this discovery? ANSWER: Matthew Meselson and Franklin Stahl Alfred Hershey and Martha Chase Erwin Chargaff Oswald Avery Frederick Griffith

C

At a specific area of a chromosome, the following sequence of nucleotides 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? ANSWER: 3' G C C T A G G 5' 5' A C G T T A G G 3' 5' G C C T A G G 3' 5' A C G U U A G G 3' 5' G C C U A G G 3'

D

In nucleotide excision repair, damaged DNA is excised by what enzyme(s)? ANSWER: DNA polymerases ligase helicase nuclease primase

D

What process repairs damage to a preexisting double helix? ANSWER: operon repair mismatch repair transformation nucleotide excision repair proofreading

D

Which of the following is an example of "recombinant DNA technology"? Hint 1. Consider what is being recombined. ANSWER: combining alternate alleles of a gene in a single cell manipulating a meiotic crossing-over event cloning genes from homologous pairs of chromosomes introducing a human gene into a bacterial plasmid alternate alleles assorting independently

D

A researcher is preparing to insert a human gene of interest into a bacterial plasmid in order to clone the human gene. She has genetically engineered the plasmid to carry a gene amp R , which confers resistance to the antibiotic ampicillin. She will include ampicillin in the plating medium when she grows the recombinant bacteria. Why has she engineered the plasmid to include an antibiotic resistance gene? Recombinant bacteria that have taken up the plasmid are vulnerable to infection and require antibiotic resistance. Recombinant bacteria that have taken up the plasmid can be recognized because they are able to survive in the presence of ampicillin. Recombinant bacteria that have taken up the plasmid can be recognized because the antibiotic resistance gene produces a blue color.

b

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized? ANSWER: Helicases and single-strand binding proteins work at the 5' end. The origins of replication occur only at the 5' end. DNA polymerase can join new nucleotides only to the 3' end of a preexisting strand. DNA ligase works only in the 3' → 5' direction.

c

Gel electrophoresis separates DNA fragments on the basis of what characteristic? ANSWER: length mutations charge restriction sites sequence

A

What are chromosomes made of? DNA and euchromatin DNA, RNA, and proteins DNA, heterochromatin, and histone proteins DNA DNA and proteins

E

Which enzyme catalyzes the elongation of a DNA strand in the 5' → 3' direction? ANSWER: helicase topoisomerase primase DNA ligase DNA polymerase III

E

DNA is a self-replicating molecule. What accounts for this important property of DNA? The nitrogenous bases of the double helix are paired in specific combinations: A with T and G with C. Replication is thermodynamically spontaneous and requires no enzymes. Its two strands are held together by easily broken covalent bonds.

A

During DNA replication, which of the following enzymes separates the DNA strands during replication? ANSWER: helicase DNA polymerase III ligase DNA polymerase I primase

A

Archaeologists unearthed a human skull with a small dried fragment of the scalp still attached. They extracted a tiny amount of DNA from the scalp tissue. How could they obtain sufficient DNA for an analysis of the ancient human's genes? ANSWER: Use a nucleic acid probe. Use the polymerase chain reaction. Subject the specimen to amniocentesis. Subject the DNA to electrophoresis. Subject the DNA to restriction enzymes

B

The figure shows circular, double-stranded DNA molecule which has double-strand break with cohesive ends made of AATT at each of 5 prime ends. Which enzyme was used to produce the molecule in the figure? ANSWER: ligase a restriction enzyme DNA polymerase RNA polymerase

B

Which of the following statements best describes the eukaryotic chromosome? ANSWER: It is composed of DNA alone. It consists of a single linear molecule of double-stranded DNA plus proteins. The number of genes on each chromosome is different in different cell types of an organism. The nucleosome is its most basic functional subunit.

B

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? ANSWER: No proofreading will occur. The DNA will supercoil. The DNA strands at the origin of replication will separate, but replication will not progress. Replication will require a DNA template from another source.

C

During DNA replication, which of the following enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments? ANSWER: helicase DNA polymerase III ligase DNA polymerase I primase

D

Cold case detectives are investigating a homicide that took place 30 years ago. In reexamining the evidence, they find a tiny spot of blood on the victim's clothing that was likely left by the murderer. The DNA in the blood has partially degraded over time. What technique(s) would the blood lab technicians use in their examination of this tiny, degraded blood sample? They would use reverse transcriptase-polymerase chain reaction (RT-PCR) to determine the genes expressed in this DNA. They would use a restriction enzyme and DNA ligase to make recombinant DNA from this sample. They would use PCR to amplify the DNA.

c

A student isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. After adding some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has the student probably LEFT OUT of the mixture? ANSWER: DNA ligase primase DNA polymerase Okazaki fragments

A

What is the role of DNA ligase in the elongation of the lagging strand during DNA replication? ANSWER: It stabilizes the unwound parental DNA. It joins Okazaki fragments together. It catalyzes the lengthening of telomeres. It synthesizes RNA nucleotides to make a primer. It unwinds the parental double helix.

B

In an analysis of the nucleotide composition of DNA, which of the following will be found? ANSWER: G + C = T + A A = C A + C = G + T A = G and C = T

C

An Okazaki fragment has which of the following arrangements? ANSWER: 5' RNA nucleotides, DNA nucleotides 3' primase, polymerase, ligase 5' DNA to 3' 3' RNA nucleotides, DNA nucleotides 5' DNA polymerase I, DNA polymerase III

A

The elongation of the leading strand during DNA synthesis __________. ANSWER: depends on the action of DNA polymerase progresses away from the replication fork occurs in the 3' → 5' direction produces Okazaki fragments

A

In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules? ANSWER: A + G = C + T A = C A = G A + T = G + C

A + G = C + T

During DNA replication, the leading strand is synthesized continuously, whereas the lagging strand is synthesized as Okazaki fragments. Why is this so? ANSWER: DNA synthesis can take place only in the 5' to 3' direction. DNA polymerases can bind to only one strand at a time. There are thousands of origins of replication on the lagging strand but only one on the leading strand.

A

For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the phosphates. Why won't this experiment work? ANSWER: Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins. Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra neutrons; therefore, they are more radioactive. There is no radioactive isotope of nitrogen. Avery et al. have already concluded that this experiment showed inconclusive results.

A

In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts? ANSWER: DNA contains phosphorus, whereas protein does not. DNA contains nitrogen, whereas protein does not. DNA contains purines, whereas protein includes pyrimidines. RNA includes ribose, whereas DNA includes deoxyribose sugars. DNA contains sulfur, whereas protein does not.

A

The leading and the lagging strands of DNA formed during DNA replication differ in that ANSWER: 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 leading strand is synthesized at twice the rate of the lagging strand. 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. the lagging strand is synthesized continuously, whereas the leading strand is synthesized in short fragments that are ultimately stitched together.

A

DNA replication is said to be semiconservative. What does this mean? The old double helix is degraded, and half of its nucleotides are used in the construction of two new double helices. Each new double helix consists of one old and one new strand. One of the two resulting double helices is made of two old strands, and the other is made of two new strands. Half of the old strand is degraded, and half is used as a template for the replication of a new strand. One strand of the new double helix is made of DNA, and the other strand is made of RNA.

B

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information based on which of the following characteristics? ANSWER: phosphate-sugar backbones the sequence of bases complementary pairing of bases different five-carbon sugars

B

The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that ANSWER: triphosphate monomers are active in the nucleoside triphosphates, but not in ATP. the nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose. the nucleoside triphosphates have two phosphate groups; ATP has three phosphate groups. ATP is found only in human cells; the nucleoside triphosphates are found in all animal and plant cells. ATP contains three high-energy bonds; the nucleoside triphosphates have two.

B

What are the repetitive DNA sequences present at the ends of eukaryotic chromosomes called? chromomeres telomeres polypeptides centromeres sarcomeres

B

Which of the following is true of DNA during interphase? ANSWER: It is in the form of highly condensed chromosomes and is unavailable for gene expression. It exists as chromatin and is less condensed than mitotic chromosomes. It is in the form of highly condensed chromosomes; it is called heterochromatin. It exists as chromatin; it is completely uncoiled and loose. It exists as chromatin and is unavailable for gene expression.

B

You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). These two classes of DNA probably represent ANSWER: Okazaki fragments and RNA primers. leading strands and Okazaki fragments. leading strands and RNA primers. RNA primers and mitochondrial DNA. lagging strands and Okazaki fragments.

B

What is meant by the description "antiparallel" regarding the two strands of nucleic acids that make up DNA? ANSWER: The twisting nature of DNA creates nonparallel strands. One strand contains only purines and the other contains only pyrimidines. The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand. Base pairings create unequal spacing between the two DNA strands.

C

What is the function of DNA polymerase III? ANSWER: to seal together the broken ends of DNA strands to unwind the DNA helix during replication to add nucleotides to the 3' end of a growing DNA strand to degrade damaged DNA molecules to rejoin the two DNA strands (one new and one old) after replication

C

Which of the following characteristics can be determined directly from X-ray diffraction photographs of crystallized DNA? ANSWER: the frequency of A versus T nucleotides the rate of replication the diameter of the helix the sequence of nucleotides

C

Which of the following modifications is most likely to alter the rate at which a DNA fragment moves through a gel during electrophoresis? ANSWER: altering the nucleotide sequence of the DNA fragment without adding or removing nucleotides radioactively labeling the cytosine bases within the DNA fragment increasing the length of the DNA fragment leaving the length of the DNA fragment the same

C

Which of the following sets of materials is required by both eukaryotes and prokaryotes for DNA replication? ANSWER: G-C rich regions, polymerases, chromosome nicks topoisomerases, telomerases, polymerases double-stranded DNA, four kinds of DNA nucleotides, primers, origins of replication ligase, primers, nucleases nucleosome loosening, four kinds of DNA nucleotides, four kinds of RNA nucleotides

C

In recombinant DNA experiments, what is used to cut pieces of DNA and what joins the resulting fragments to form recombinant DNA? ANSWER: a transposon ... a plasmid a transposon ... a restriction enzyme a plasmid ... DNA ligase a restriction enzyme ... DNA ligase DNA ligase ... a restriction enzyme

D

In the Hershey and Chase experiment that helped confirm that DNA, not protein, was the hereditary material, what was the key finding? Radioactively labeled sulfur was found outside of the infected bacteria. Radioactively labeled phosphorus was found outside of the infected bacteria. Radioactively labeled sulfur was present inside the infected bacteria. Radioactively labeled phosphorus was present inside the infected bacteria. Radioactively labeled carbon was present inside the infected bacteria.

D

What is the function of helicase in DNA replication? ANSWER: It adds nucleotides to the new strand in the 5' to 3' direction. It joins together Okazaki fragments. It checks for errors in the newly synthesized DNA strand. It untwists the double helix and separates the two DNA strands. It relieves strain from twisting of the double helix as it is unwound.

D

What is the function of topoisomerase? ANSWER: stabilizing single-stranded DNA at the replication fork unwinding of the double helix elongating new DNA at a replication fork by adding nucleotides to the existing chain relieving strain in the DNA ahead of the replication fork adding methyl groups to bases of DNA

D

Which of the following enzymes synthesizes short segments of RNA? ANSWER: helicase DNA polymerase III ligase DNA polymerase I primase

E

Which of the following statements accurately describes why Taq polymerase is used in PCR? ANSWER: It has regions that are complementary to the primers. It is heat stable, and it binds more readily than other polymerases to the primers. It binds more readily than other polymerases to the primers. Only minute amounts are needed for each cycle of PCR. It is heat stable and can withstand the heating step of PCR.

E

Who conducted the X-ray diffraction studies that were key to the discovery of the structure of DNA? McClintock Griffith Chargaff Meselson and Stahl Franklin

E