DNA Replication Overview
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Questions and Answers

What direction does DNA polymerase proofread the newly synthesized strand?

  • 5' to 3'
  • Both 5' to 3' and 3' to 5'
  • In a random direction
  • 3' to 5' (correct)

What is the primary function of DNA polymerase I in the lagging strand synthesis?

  • To connect Okazaki fragments
  • To replace RNA primers with DNA nucleotides (correct)
  • To continue strand elongation
  • To synthesize primers

Which components make up the primosome during DNA replication?

  • Helicase and Okazaki fragments
  • Primase and other associated proteins (correct)
  • Exonuclease and ligase
  • DNA polymerase I and II

What are Okazaki fragments associated with?

<p>The lagging strand synthesis (A)</p> Signup and view all the answers

What characteristic describes the leading strand during DNA replication?

<p>Synthesized continuously (B)</p> Signup and view all the answers

How do pseudonucleotides affect DNA synthesis?

<p>They stop further elongation of the DNA chain (D)</p> Signup and view all the answers

What is the main role of DNA ligase in DNA replication?

<p>To stitch together Okazaki fragments (C)</p> Signup and view all the answers

Which enzymatic function is specific to DNA polymerase III as compared to DNA polymerase I?

<p>Adding nucleotides to the leading strand (D)</p> Signup and view all the answers

Which statement about the lagging strand is true?

<p>It is synthesized in fragments called Okazaki fragments. (B)</p> Signup and view all the answers

What is the primary function of DNA-A protein in the replication process?

<p>To separate DNA strands at the point of origin. (C)</p> Signup and view all the answers

What unique feature do modified pseudonucleotides possess?

<p>They lack the OH group on carbon #3 (D)</p> Signup and view all the answers

What happens to the DNA strands once they are separated at the point of origin?

<p>They form a replication bubble. (C)</p> Signup and view all the answers

Which enzyme is responsible for unwinding the DNA spiral during replication?

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

What is the function of Topoizomerase during DNA replication?

<p>To resolve supercoils in DNA. (D)</p> Signup and view all the answers

How do Quinolones affect bacterial Topoizomerase, and what consequence does it have?

<p>They inactivate the ligase domain, leading to DNA degradation. (B)</p> Signup and view all the answers

What is the role of the RNA primer produced by Primase in DNA replication?

<p>To provide a 3' end for DNA polymerase. (C)</p> Signup and view all the answers

Which domain of Topoizomerase is responsible for cutting the DNA strands?

<p>Nuclease domain only. (C)</p> Signup and view all the answers

What is the directionality in which DNA polymerase reads the template DNA during replication?

<p>3' to 5' (D)</p> Signup and view all the answers

What characteristic distinguishes Topoizomerase 2 from other types of Topoizomerases?

<p>It has two nuclease domains and cuts both strands. (D)</p> Signup and view all the answers

What is the result of Helicase activity on the DNA strands during replication?

<p>Formation of supercoils. (B)</p> Signup and view all the answers

Flashcards

Origin of Replication

A specific DNA sequence rich in adenine (A) and thymine (T) bases where DNA replication begins.

Helicase

An enzyme that unwinds the DNA double helix at the origin of replication, separating the two strands.

Single-Strand Binding Proteins (SSBs)

Proteins that bind to single-stranded DNA to prevent them from re-pairing or being degraded by enzymes.

Topoisomerase

An enzyme that relieves the tension caused by the unwinding of DNA during replication.

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Primer

A short RNA sequence that serves as a starting point for DNA polymerase to begin synthesizing a new DNA strand.

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DNA Polymerase

An enzyme that adds nucleotides to a growing DNA strand, using a template strand as a guide.

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5' to 3' Direction of DNA Synthesis

DNA polymerase can only add nucleotides to the 3' end of a growing DNA strand.

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DNA Replication

The process of copying a DNA molecule to produce two identical DNA molecules.

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Antibiotics Targeting Topoisomerase

Antibiotics like Quinolones that target bacterial topoisomerase, disrupting DNA replication and leading to bacterial death.

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Cancer Drugs Targeting Topoisomerase

Cancer drugs like Etoposides and Teniposides that inhibit topoisomerase in human cells, preventing uncontrolled DNA replication in cancer cells.

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DNA Polymerase III Proofreading

DNA polymerase III reads the template strand in the 3' to 5' direction and adds nucleotides to the new DNA strand in the 5' to 3' direction. This process is highly accurate, but mistakes can happen. If an error is detected, the enzyme can use its exonuclease domain to remove the incorrect nucleotide and replace it with the correct one. This proofreading mechanism ensures high fidelity in DNA replication.

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Leading Strand

The new DNA strand synthesized continuously in the direction of the replication fork.

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Lagging Strand

The new DNA strand synthesized discontinuously in fragments away from the replication fork.

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Primosome

The enzyme Primase works with other proteins to synthesize RNA primers, which are short sequences needed to initiate DNA replication.

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Okazaki Fragments

Short fragments of DNA that are joined together to form the lagging strand. They are synthesized in a discontinuous manner due to the movement of the replication fork.

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DNA Polymerase 1 Function

DNA polymerase I removes the RNA primers from the lagging strand and replaces them with DNA nucleotides.

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DNA Ligase

An enzyme used to join the ends of Okazaki fragments on the lagging strand. It creates a continuous, uninterrupted DNA molecule by sealing the gaps between fragments.

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Pseudonucleotides

A class of drugs that inhibit DNA replication by incorporating modified nucleotides into the growing DNA chain. These drugs are often used as antiviral or anticancer agents.

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Exonuclease Activity

The ability of some DNA polymerases, including DNA polymerase III, to remove mismatched nucleotides during DNA replication, ensuring accurate DNA synthesis.

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Study Notes

DNA Replication

  • Replication begins by separating DNA strands at specific locations rich in A and T bases, called origins or consensus areas.
  • Bacterial DNA has a single origin, while eukaryotic DNA has multiple.
  • DNA helicase separates the DNA strands, creating a replication bubble.
  • Single-strand binding proteins (SSBs) stabilize the separated strands to prevent reannealing.
  • Topoisomerases relieve the strain caused by unwinding the DNA helix.
  • RNA primers are synthesized by primase to provide a 3' hydroxyl group for DNA polymerase to start adding nucleotides.
  • DNA polymerase III adds nucleotides to the 3' end of the growing DNA strand, building in the 5' to 3' direction.
  • Leading strand synthesis is continuous in the direction of the replication fork.
  • Lagging strand synthesis is discontinuous, creating Okazaki fragments.
  • DNA polymerase I removes RNA primers and replaces them with DNA nucleotides.
  • DNA ligase joins Okazaki fragments together.

Topoisomerases

  • Topoisomerases are enzymes that relieve strain on the DNA molecule by breaking and rejoining DNA strands.
  • Two types of topoisomerases are discussed: Type I and Type II.
  • Type I topoisomerases break and rejoin one strand of the DNA helix.
  • Type II topoisomerases break and rejoin both strands of the DNA helix, helping to resolve supercoils.
  • Some antibiotics target topoisomerases to inhibit bacterial DNA replication.

DNA Polymerases

  • DNA polymerase is an enzyme that catalyzes the synthesis of DNA.
  • There are multiple types of DNA polymerases in the cell.
  • DNA polymerase III is the primary enzyme responsible for DNA replication.
  • DNA polymerase I removes RNA primers and fills in the gaps in the lagging strand.
  • Different types of DNA polymerases have specialized functions, including DNA repair and replication of specific regions of the genome.

Anti-cancer Drugs

  • Some drugs interfere with topoisomerases, inhibiting DNA replication.
  • Some drugs interfere with nucleotides, introducing errors in DNA replication.

Antiviral Drugs

  • Some drugs interfere with nucleotides, altering DNA structure and causing defects in the replication of the viral genome.

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DNA Replication PDF

Description

This quiz focuses on the intricate process of DNA replication, covering key components such as DNA helicase, topoisomerases, and the roles of DNA polymerase and ligase. It explores the differences between bacterial and eukaryotic DNA replication, including leading and lagging strand synthesis. Test your knowledge on these fundamental concepts essential for understanding molecular biology.

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