Chapter 16 BIOL-102-11
A sample of double-stranded DNA contains 28% thymine. Approximately what percent of the nucleotides in this sample will be guanine?
Answer: 22%
Suppose a 100-base-pair, double-stranded DNA molecule consists of 15% thymine bases. How many total hydrogen bonds are holding the two strands together?
Answer: 270
Use the figure to answer the following question. Referring to the figure, what bases will be added as DNA replication proceeds on the bottom strand?
Answer: 5′ A, G, A, C, G, A, C 3′
A sample of double-stranded DNA contains 42% cytosine. Approximately what percent of the nucleotides in this sample will be thymine?
Answer: 8%
What is the Chargaff's rule?
Answer: A (adenine) pairs with T (thymine) / G (guanine) pairs with C (cytosine).
Which of the following combinations of base pairs will be found in a molecule of DNA?
Answer: A + C = G + T
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
DNA strands are antiparallel. Which of the following statements defines "antiparallel"?
Answer: A 5' to 3' DNA strand is paired with the 3' to 5' DNA strand.
Use the figure to answer the following question. A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in "heavy" (radioactive) nitrogen (15N) for several generations and then transfer them to 14N medium. Which pattern in the figure would you expect if the DNA was replicated in a conservative manner?
Answer: B
What is the 5′ → 3′ sequence on the anticodon of the Tryptophan (Trp) tRNA?
Answer: CCA
Use the figure to answer the following question. In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" (radioactive) nitrogen (15N) and then transferred them to a medium containing 14N (non-radioactive). Which of the results in the figure would be expected after one round of DNA replication in the presence of 14N?
Answer: D
A student isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds 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 she probably left out of the mixture?
Answer: DNA ligase
In bacteria, which of the following proteins is responsible for removing nucleotides from the RNA primer that is used for initiation DNA synthesis?
Answer: DNA pol I
What catalyzes the formation of phosphodiester bonds between a DNA strand and a new nucleotide being added during DNA replication?
Answer: DNA polymerase
In E. coli, which enzyme catalyzes the elongation of a new DNA strand in the 5' → 3' direction?
Answer: DNA polymerase III
Which of the following is a reason that a new DNA strand elongates only in the 5' to 3' direction during DNA replication?
Answer: DNA polymerase begins adding nucleotides at the 3' end of the template.
What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?
Answer: DNA polymerase can join new nucleotides only to the 3' end of a pre-existing strand, and the strands are antiparallel.
The lagging strand is characterized by a series of short segments of DNA (Okazaki fragments) that are 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?
Answer: DNA polymerase synthesizes leading and lagging strands during replication only in one direction.
Which of the following statements correctly describes the structure of chromatin?
Answer: Heterochromatin is highly condensed, whereas euchromatin is less compact.
Which answer best describes the role of telomerase in replicating the ends of linear chromosomes?
Answer: It catalyzes the lengthening of telomeres, compensating for the shortening that could occur during replication without telomerase activity.
Which of the following statements accurately describes the structure of a eukaryotic chromosome?
Answer: It is a single linear molecule of double-stranded DNA plus proteins.
What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?
Answer: It joins Okazaki fragments together
Within a double-stranded DNA molecule, if adenine forms hydrogen bonds with thymine, and cytosine forms hydrogen bonds with guanine what consequence in the structure of the DNA?
Answer: It permits complementary base pairing.
Consider the replication bubble diagrammed at the right. Which letters represent strands with Okazaki fragments?
Answer: M and N
Which of the following statements accurately describes differences between DNA replication in prokaryotes and DNA replication in eukaryotes?
Answer: Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.
Which of the following is a reason that the low error rate of DNA replication is important to evolution?
Answer: Rare errors are the source of variation.
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. Which of the following best explains the effect of telomerase on cellular aging?
Answer: Telomerase can eliminate telomere shortening and slows aging.
Which of the following statements correctly describes the difference between the leading strand and the lagging strand in DNA replication?
Answer: The leading strand is synthesized continuously in the 5'→ 3' direction, while the lagging strand is synthesized discontinuously in the 5'→ 3' direction.
Which of the following statements correctly describes the difference between the leading and the lagging strands of DNA in DNA replication?
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.
Which of the following statements correctly describes the difference between ATP used in metabolism and the nucleotides used as a building block during DNA synthesis?
Answer: The nucleotides have the sugar deoxyribose; ATP has the sugar ribose.
Semiconservative model?
Answer: When a double helix replicates, each daughter molecule will have one old strand and one newly made strand.
A replication error results in a zygote that has inactive telomerase, which of the following characteristics would you expect to see in the organism that develops?
Answer: a reduction in chromosome length in gametes
The elongation of the leading strand during DNA synthesis ________.
Answer: depends on the action of DNA polymerase
In a nucleosome, the DNA is wrapped around ________.
Answer: histones
DNA is isolated from bacteria undergoing DNA replication. After heat treatment to disrupt H-bonds the DNA is centrifuged and it separates into two classes. One class of 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). Which types of DNA do the two classes most likely represent?
Answer: leading strands and Okazaki fragments
Which list the provides the correct enzyme order required for nucleotide excision repair of a thymine dimer?
Answer: nuclease, DNA polymerase, DNA ligase
Which of the following lists represents the order of increasingly higher levels of organization of chromatin?
Answer: nucleosome, 30-nm chromatin fiber, looped domain
E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment?
Answer: one low-density and one intermediate-density band
Semiconservative replication involves a template. Which of the following best describes the template molecule?
Answer: one strand of the DNA molecule
What is the function of the enzyme topoisomerase in DNA replication?
Answer: relieving strain in the DNA ahead of the replication fork caused by the untwisting of the double helix
Which of the following types of molecules help to hold the DNA strands apart while they are being replicated?
Answer: single-strand DNA binding proteins
In DNA polymerization, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and which of the following atoms or molecules of the last nucleotide in the polymer?
Answer: the 3' OH
What are telomeres?
Answer: the ends of linear chromosomes
In bacteria, what is the function of DNA polymerase III?
Answer: to add nucleotides to the 3' end of a growing DNA strand