Test 4 Chapter 10 Flashcards
Which of the following terms accurately describes the replication of DNA in vivo?
semidiscontinuous
DNA polymerase III adds nucleotides ________.
to the 3’ end of the RNA primer
DNA polymerase I is thought to add nucleotides ________.
in the place of the primer RNA after it is removed
Which terms accurately reflect the nature of replication of the chromosome in E. Coli?
bidirectional and fixed point of initiation
Which cluster of terms accurately reflects the nature of DNA replication in prokaryotes?
fixed point of initiation, bidirectional, semiconservative
The discontinuous aspect of replication of DNA in vivo is caused by ________.
the 5’ to 3’ polarity restriction
Structures located at the ends of eukaryotic chromosomes are called ________.
telomeres
Assume that a culture of E. coli was grown for approximately 50 generations in 15N (provided in the medium in the ammonium ion), which is a heavy isotope of nitrogen (14N). You extract the DNA from the culture, and it has a density of 1.723 gm/cm3 (water = 1.00 gm/cm3). From the literature, you determine that DNA containing only the common form of nitrogen, 14N, has a density of 1.700 gm/cm3. Bacteria from the 15N culture were washed in buffer and transferred to 14N medium for one generation immediately after which the DNA was extracted and its density determined
(a) What would be the expected density of the extracted DNA?
approximately 1.712
Assume that a culture of E. coli was grown for approximately 50 generations in 15N (provided in the medium in the ammonium ion), which is a heavy isotope of nitrogen (14N). You extract the DNA from the culture, and it has a density of 1.723 gm/cm3 (water = 1.00 gm/cm3). From the literature, you determine that DNA containing only the common form of nitrogen, 14N, has a density of 1.700 gm/cm3. Bacteria from the 15N culture were washed in buffer and transferred to 14N medium for one generation immediately after which the DNA was extracted and its density determined
After you heat the extracted DNA until it completely denatures (95°C for 15 minutes), what would you expect the density of the DNA in the denatured extract to be? For the purposes of this question, assume that DNA has the same density regardless of whether it is single- or double-stranded.
1.723 and 1.700
Assume that a culture of E. coli was grown for approximately 50 generations in 15N (provided in the medium in the ammonium ion), which is a heavy isotope of nitrogen (14N). You extract the DNA from the culture, and it has a density of 1.723 gm/cm3 (water = 1.00 gm/cm3). From the literature, you determine that DNA containing only the common form of nitrogen, 14N, has a density of 1.700 gm/cm3. Bacteria from the 15N culture were washed in buffer and transferred to 14N medium for one generation immediately after which the DNA was extracted and its density determined
Assuming that the molar percentage of adenine in the extracted DNA was 20%, what would be the expected molar percentages of the other nitrogenous bases in this DNA?
thymine = 20%, guanine = 30%, cytosine = 30%
Assume that a culture of E. coli was grown for approximately 50 generations in 15N (provided in the medium in the ammonium ion), which is a heavy isotope of nitrogen (14N). You extract the DNA from the culture, and it has a density of 1.723 gm/cm3 (water = 1.00 gm/cm3). From the literature, you determine that DNA containing only the common form of nitrogen, 14N, has a density of 1.700 gm/cm3. Bacteria from the 15N culture were washed in buffer and transferred to 14N medium for one generation immediately after which the DNA was extracted and its density determined
Assume that a fraction of the extracted DNA was digested to completion with the enzyme snake venom diesterase. This enzyme cleaves between the phosphate and the 3’ carbon. Present a “simplified” diagram that would illustrate the structure of the predominant resulting molecule.
Section 10.1 Its a diagram
What three possible models were suggested to originally describe the nature of DNA replication?
conservative, semiconservative, dispersive
The Meselson and Stahl experiment provided conclusive evidence for the semiconservative replication of DNA in E. Coli. What pattern of bands would occur in a CsCl gradient for conservative replication?
After one generation in the 14N, there would be two bands, one heavy and one light (no intermediate). After the second generation in the 14N, there would also be two bands, one heavy and one light (no intermediate).
Meselson and Stahl determined that DNA replication in E. coli is semiconservative. What additive did they initially supply to the medium in order to distinguish “new” from “old” DNA?
15N
Briefly describe what is meant by the term autoradiography and identify a classic experiment that used autoradiography to determine the replicative nature of DNA in eukaryotes.
Autoradiography is a technique that allows an isotope to be detected within a cell; the Taylor, Woods, and Hughes (1957) experiment used 3H-thymidine.
What primary ingredients, coupled with DNA polymerase I, are needed for the in vitro synthesis of DNA?
dNTP, DNA template, primer DNA or RNA, Mg++ (appropriate buffering, temperature, and salt concentrations might be considered “secondary” ingredients)
DNA replication in vivo requires a primer with a free 3’ end. What molecular species provides this 3’ end, and how is it provided?
The free 3’ end is provided by an RNA primer; it is provided by the enzymatic activity of RNA primase.
Given the diagram below, assume that a G1 chromosome (left) underwent one round of replication in 3H-thymidine and the metaphase chromosome (right) had both chromatids labeled. Which of the following replicative models (conservative, dispersive, semiconservative) could be eliminated by this observation?
conservative
Each of the following terms refers to the replication of chromosomes. Describe the role (relationship) of each in (to) chromosome replication.
Okazaki fragment
Okazaki fragment is a short single-stranded stretch of DNA on the lagging strand.
Each of the following terms refers to the replication of chromosomes. Describe the role (relationship) of each in (to) chromosome replication.
lagging strand
Lagging strand is the side of the replication fork where synthesis is discontinuous.
Each of the following terms refers to the replication of chromosomes. Describe the role (relationship) of each in (to) chromosome replication.
bidirectional
Bidirectional indicates that from the point of initiation, replication occurs in both directions along the DNA.
List four enzymes known to be involved in the replication of DNA in bacteria.
Appropriate answers would include any four of the following: DNA polymerase I, DNA polymerase III, ligase, RNA primase, helicase, gyrase
Which structural circumstance in DNA sets up the requirement for the semidiscontinuous nature of its replication?
5’ > 3’ polarity restrictions of DNA synthesis and the antiparallel orientation of the DNA strands in DNA
As unwinding of the helix occurs during DNA replication, tension is created ahead of the replication fork. Describe the nature of this tension and state the manner in which it is resolved.
supercoiling; DNA gyrase
