Meselson and Stahl Experiments on DNA Replication

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Questions and Answers

What type of DNA replication gives rise to two duplexes, one containing two old strands and the other containing two new strands?

  • Initiation replication
  • Semiconservative replication
  • Conservative replication (correct)
  • Dispersive replication

What did the experiments by Meselson and Stahl (1958) support in terms of DNA replication?

  • Initiation of replication
  • Dispersive replication model
  • Semiconservative replication model (correct)
  • Conservative replication model

In DNA replication, what gives rise to two replication forks?

  • Prokaryotic cells
  • Origin of replication (correct)
  • Eukaryotic cells
  • Semiconservative replication

In the fourth generation of DNA, what would be the composition in terms of low- and intermediate-density?

<p>One low-density and one intermediate-density strand (A)</p> Signup and view all the answers

What did Alfred Hershey and Martha Chase's experiment demonstrate?

<p>DNA is the genetic material (B)</p> Signup and view all the answers

Which isotopic medium was used to label the viral proteins in Alfred Hershey and Martha Chase's experiment?

<p>Radioactive sulphur (35S) (C)</p> Signup and view all the answers

What viral component was radioactively labeled when using radioactive phosphorus (32P) in the experiment?

<p>DNA (A)</p> Signup and view all the answers

How is DNA replication described?

<p>Semiconservative replication gives two duplex DNA molecules, each of which contains one old strand and one new strand (A)</p> Signup and view all the answers

What is the main focus of Dr. Mark Carlile's lecture on DNA replication?

<p>Nucleic acid biochemistry (C)</p> Signup and view all the answers

According to Dr. Mark Carlile, what knowledge should students gain about DNA replication?

<p>The biochemical processes used in DNA replication (C)</p> Signup and view all the answers

In Watson and Crick's paper, what did they suggest about the genetic material?

<p>It has a copying mechanism (A)</p> Signup and view all the answers

Why is DNA a helix, according to Dr. Mark Carlile?

<p>Chemical reasons (B)</p> Signup and view all the answers

What is the role of the primer in DNA replication?

<p>To proofread the newly synthesized strand (D)</p> Signup and view all the answers

How is the primer removed during DNA replication?

<p>By exonuclease activity of the polymerase complex (A)</p> Signup and view all the answers

What is the function of the topoisomerase enzymes in DNA replication?

<p>To introduce a break in one strand and pass the other strand through (C)</p> Signup and view all the answers

Which enzyme is responsible for joining the Okazaki fragments in DNA replication?

<p>Ligase enzyme (D)</p> Signup and view all the answers

What happens to DNA polymerase III during the joining of Okazaki fragments?

<p>It is replaced by another polymerase (Pol I) (D)</p> Signup and view all the answers

Why do replication forks require topoisomerases during DNA replication?

<p>To alleviate topological problems caused by over-winding of the double helix (D)</p> Signup and view all the answers

What was the result of Alfred Hershey and Martha Chase's experiment using radioactive phosphorus (32P)?

<p>The bacterial pellet was non-radioactive when infected by the 35S–viruses. (C)</p> Signup and view all the answers

What was the viral component that was radioactively labeled when using radioactive sulphur (35S) in Alfred Hershey and Martha Chase's experiment?

<p>Proteins (C)</p> Signup and view all the answers

What is the description of semiconservative replication, as mentioned by Dr. Mark Carlile?

<p>It gives rise to two duplex DNA molecules, each containing one old strand and one new strand. (B)</p> Signup and view all the answers

In DNA replication, what is the function of topoisomerases?

<p>To unwind the DNA double helix. (D)</p> Signup and view all the answers

What is the role of the primer in DNA replication?

<p>To initiate DNA replication by providing a starting point for DNA polymerase (A)</p> Signup and view all the answers

Why are two DNA polymerase enzymes tethered together during DNA replication?

<p>To replicate both strands of DNA simultaneously (D)</p> Signup and view all the answers

What is the function of topoisomerase enzymes during DNA replication?

<p>To alleviate topological problems by resolving over-winding of the double helix (C)</p> Signup and view all the answers

Which enzyme is responsible for removing the RNA primer on the Okazaki fragment prior to ligation?

<p>DNA polymerase I (D)</p> Signup and view all the answers

What problem do replication forks face if they progress a short distance without topoisomerases?

<p>Over-winding of the double helix (D)</p> Signup and view all the answers

What is the enzyme that joins the Okazaki fragments together during DNA replication?

<p>Ligase (C)</p> Signup and view all the answers

What role does the regulatory mechanism play in E. coli DNA replication?

<p>It signals the completion of DNA replication once the replicons meet at a specific point (C)</p> Signup and view all the answers

What is a distinguishing factor between eukaryotic and prokaryotic DNA replication forks?

<p>Eukaryotic replication forks move at around 50 base pairs per second due to the complexity of eukaryotic DNA structures (A)</p> Signup and view all the answers

What is the function of topoisomerase enzymes in DNA replication?

<p>They are responsible for unlinking the interlinked daughter DNA molecules (B)</p> Signup and view all the answers

What happens to the separated DNA molecules after unlinking by topoisomerase enzymes?

<p>They are segregated and await cell division, where each cell will receive a DNA molecule (C)</p> Signup and view all the answers

What is the function of DnaA proteins in the initiation of DNA replication in prokaryotes?

<p>They open up a local AT-rich region of the DNA via torsional stress. (A)</p> Signup and view all the answers

What is the primary function of SSBs (single-stranded binding proteins) during DNA replication initiation in prokaryotes?

<p>To prevent the strands from re-annealing and protect the DNA from attack by free radicals and nuclease enzymes. (D)</p> Signup and view all the answers

What is the role of the DNA-dependent DNA polymerase enzymes during DNA replication?

<p>Carrying out synthesis of the new strand in the 5’ to 3’ direction. (A)</p> Signup and view all the answers

What is the main function of the Primase enzyme (DnaG) during prokaryotic elongation in DNA replication?

<p>Synthesizing the RNA primer on the leading strand. (B)</p> Signup and view all the answers

What is the role of topoisomerase enzymes in DNA replication?

<p>Alleviating torsional stress on the DNA molecule by causing temporary nicks in the DNA backbone. (A)</p> Signup and view all the answers

What is the function of DnaB (Helicase enzyme) during replication initiation in prokaryotes?

<p>Breaking base-pairs (hydrogen bonds) at the replication fork. (B)</p> Signup and view all the answers

What was the concluding statement in Watson and Crick's paper about the DNA double helix?

<p>It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.</p> Signup and view all the answers

What is the primary focus of Dr. Mark Carlile's lecture on DNA replication?

<p>The biochemical processes used in the replication of DNA in prokaryotes and eukaryotes, the experiments used to understand DNA replication, and how DNA replication is controlled as part of the cell cycle.</p> Signup and view all the answers

Why is DNA a helix, according to Dr. Mark Carlile?

<p>DNA is a helix due to its specific pairing, which suggests a possible copying mechanism for the genetic material.</p> Signup and view all the answers

What is the distinguishing factor between eukaryotic and prokaryotic DNA replication forks?

<p>The distinguishing factor is that eukaryotic DNA replication forks have multiple origins of replication, while prokaryotic DNA replication forks have a single origin of replication.</p> Signup and view all the answers

What are the three subunits of the core polymerase?

<p>α, ε, θ</p> Signup and view all the answers

Which subunit is responsible for dimerization of the core DNA polymerase?

<p>Ï„</p> Signup and view all the answers

How many subunits comprise the sliding clamp and what is its function?

<p>Two homodimers of the β subunit; provides the ring structure needed for processivity</p> Signup and view all the answers

Name the five subunits with clamp-loader functions.

<p>γ, δ, δ', χ, ψ</p> Signup and view all the answers

According to Meselson and Stahl's experiment, what would be the composition (in terms of low- and intermediate-density) of the fourth generation DNA?

<p>Half low-density and half intermediate-density</p> Signup and view all the answers

What is the initiating point for replication in both prokaryotes and eukaryotes, and what does it give rise to?

<p>Origin of replication; gives rise to two replication forks</p> Signup and view all the answers

What is the term for the branch point in a replication eye where DNA synthesis occurs, and what is the significance of this point?

<p>Replication fork; DNA synthesis occurs at this point</p> Signup and view all the answers

What did Meselson and Stahl's experiments in 1958 support in terms of the model of DNA replication?

<p>Semiconservative replication model</p> Signup and view all the answers

What is the minimum length of a DNA molecule that will support replication in yeast?

<p>11 bp</p> Signup and view all the answers

How many replicons are required per mammalian cell DNA in eukaryotic replication?

<p>50,000 - 100,000</p> Signup and view all the answers

What is believed to initiate replication in areas of repetitive DNA sequence in mammals?

<p>Random initiation</p> Signup and view all the answers

Why can eukaryotic DNA replicons only initiate once per cell?

<p>To fully and controllably replicate DNA prior to cell division</p> Signup and view all the answers

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