Chapter 11: DNA Replication & Recombination Flashcards
True or False?
The data obtained from the Meselson–Stahl experiment after one generation of replication eliminated the dispersive model of DNA replication.
False
The data obtained from the Meselson–Stahl experiment after one generation was consistent with both the semiconservative and the dispersive model of DNA replication. The conservative model of DNA replication was eliminated because it predicted that there would be two bands representing the original DNA at one density and the newly replicated DNA at a different density.
Which enzyme catalyzes the addition of nucleotides to a growing DNA chain?
DNA polymerase catalyzes the addition of nucleotides to a growing DNA chain.
Single‑strand binding proteins stabilize the open conformation of the unwound DNA.
Once helicase unwinds the double helix, single‑strand binding proteins bind to the open DNA and prevent it from winding together again.
The results of the Meselson-Stahl experiments relied on all of the following:
a cesium chloride gradient
a means of distinguishing among the distribution patterns of newly synthesized and parent molecule DNA possible
that a heavy isotope of nitrogen could be incorporated into replicating DNA molecules
The results of the Meselson-Stahl experiments relied on all of the following except _______.
the fact that DNA is the genetic material
This fact had already been established and was not of any consequence in these experiments.
After observing the results of one round of replication, the scientists obtained results from a second round. The purpose of one additional round of replication was to _______.
distinguish between semi-conservative and dispersive replication.
After one round of replication, the results of these two possibilities are indistinguishable. A second round was required to distinguish between these two possibilities.
Which of the following would result from a third round of replication using the methods of Meselson and Stahl?
One light band and one intermediate band
Of the molecules generated in the third round, 75% are completely light, 25% are intermediate.
In the Meselson-Stahl experiment, which mode of replication was eliminated based on data derived after one generation of replication?
conservative
The conservative replication theory says that parental strands reanneal with parental strands, and daughter strands reanneal with daughter strands after DNA replication. This experiment showed that this was not the case.
Both the dispersive and semi-conservative models predicted that after one round of replication, there would be one half-heavy band. In the dispersive model, the original heavy band has been dispersed evenly into the two daughter molecules, both of which also contain ½ light nitrogen. In the semi-conservative model, each new daughter molecule contains one heavy strand (from the parent molecule) and one light strand (newly synthesized). Since the DNA does not denature on the gradient, one half-heavy band would be predicted by both models, which is what was seen. The conservative model predicted that there would be two bands: one heavy (containing both original heavy parent strands) and one light band (both strands newly synthesized). Thus, the first-round data ruled it out.
After two rounds of replication, the semi-conservative model predicts two bands: one light band (daughter molecules with all new nucleotides) and one half-heavy band (containing one of the parent strands and one new, light strand) while the dispersive model predicts only one ¼ heavy band. Since one-half heavy and one light band was seen, the dispersive model was eliminated and the semi-conservative model was supported.
True or False?
In the Meselson and Stahl (1958) experiment, bean plants (Vicia faba) were radioactively labeled so that autoradiographs could be made of chromosomes.
False
What enzyme or function is being affected in Mutant (a), causing many mismatched base pairs?
Mutant (a): Newly synthesized DNA contains many mismatched base pairs.
no DNA repair
What enzyme or function is being affected in Mutant (b), causing the accumulation of Okazaki fragments and failure to complete DNA synthesis?
Mutant (b): Okazaki fragments accumulate, and DNA synthesis is never completed.
no DNA ligase activity
What enzyme or function is being affected in Mutant (c), causing DNA synthesis to never be initiated?
Mutant (c): No initiation occurs.
no Primase activity
What enzyme or function is being affected in Mutant (d), causing DNA synthesis to be very slow?
Mutant (d): Synthesis is very slow.
only DNA polymerase I activity
What enzyme or function is being affected in Mutant (e), causing supercoiled DNA to remain after replication?
Mutant (e): Supercoiled strands remain after replication, which is never completed.
no DNA gyrase activity
What are the requirements for in vitro synthesis of DNA under the direction of DNA polymerase I?
DNA template, a divalent cation (Mg++ ), and all 4 of the deoxyribonucleoside triphosphates: dATP, dCTP, dTTP, and dGTP.
All of the following are differences between eukaryotic and prokaryotic DNA replication:
the rate of DNA synthesis
the number of replication origins
the type and number of polymerases involved in DNA synthesis
Which of the following is NOT different between eukaryotic and prokaryotic DNA replication?
the ability to form a replication fork
Both prokaryotes and eukaryotes form replication forks during DNA replication.
All of the following are related to telomeres:
telomerase enzyme
links to the aging process
short tandem repeats located at the ends of telomeres
True or False?
Telomeres are found in eukaryotes and prokaryotes.
FALSE
Telomeres are found in eukaryotes but not prokaryotes.
Structures located at the ends of eukaryotic chromosomes are called ________.
telomeres
True or False?
Telomerase is an RNA-containing enzyme that adds telomeric DNA sequences onto the ends of linear chromosomes.
True
Which structures can be involved in recombination?
Chromatids of homologous chromosomes
Chromatids of homologous chromosomes can recombine during meiosis.
The process that determines the length of heteroduplex DNA on the chromatids is called branch migration.
True
The crossbridge DNA structure formed after the initial nick is sealed can migrate along the chromatid. This process is called branch migration, and it increases the length of heteroduplex DNA.
Which process does not occur during recombination?
DNA polymerization
Recombination does not include the synthesis of new DNA.