DNA Replication Overview
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Questions and Answers

What is the primary function of DNA polymerase I?

  • To remove RNA phosphodiester bonds and replace them with DNA nucleotides. (correct)
  • To synthesize RNA primers for DNA replication.
  • To proofread DNA strands from 5' to 3'.
  • To synthesize DNA continuously without interruptions.

Which statement accurately describes the lagging strand in DNA replication?

  • It is synthesized in the 5' to 3' direction without any interruptions.
  • It consists of shorter fragments called Okazaki fragments. (correct)
  • It is synthesized continuously towards the replication fork.
  • It is produced in long, continuous segments as the DNA unzips.

How do pseudonucleotides affect DNA replication?

  • They serve as primers for new DNA synthesis.
  • They disrupt the replication process by halting further elongation of the DNA chain. (correct)
  • They are recognized and utilized by DNA polymerases to increase efficiency.
  • They enhance the elongation of the DNA chain significantly.

What role does the enzyme Primase play in DNA replication?

<p>It forms a complex with the Primosome to create RNA primers. (C)</p> Signup and view all the answers

What distinguishes the leading strand from the lagging strand during DNA replication?

<p>The leading strand is synthesized continuously towards the replication fork, while the lagging strand is not. (B)</p> Signup and view all the answers

Which enzyme is primarily responsible for stitching together Okazaki fragments?

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

In which direction does DNA polymerase proofread the new strand?

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

What happens when DNA polymerase I encounters a pseudonucleotide during DNA synthesis?

<p>It incorporates the modified nucleotide, stopping further elongation. (A)</p> Signup and view all the answers

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

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

Which of the following statements about Okazaki fragments is true?

<p>They are ligated by DNA Ligase after synthesis. (D)</p> Signup and view all the answers

What is the primary challenge that DNA polymerase I addresses?

<p>Replacing RNA nucleotides with DNA nucleotides on the lagging strand. (B)</p> Signup and view all the answers

How does Topoizomerase resolve the supercoils created during DNA replication?

<p>By cutting one strand of DNA and repairing it with its ligase domain. (C)</p> Signup and view all the answers

What unique feature does Topoizomerase 2 exhibit compared to other types of Topoizomerases?

<p>It can cut both strands of DNA simultaneously. (A)</p> Signup and view all the answers

What is the consequence of antibiotics like Quinolones on bacterial DNA?

<p>They deactivate the ligase domain while stimulating the nuclease domain of Topoizomerase. (B)</p> Signup and view all the answers

What does the enzyme Primase accomplish during DNA replication?

<p>It forms a primer that provides a free 3' end for DNA polymerization. (D)</p> Signup and view all the answers

In what direction does DNA polymerase synthesize the new DNA strand during replication?

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

What initiates the formation of a replication bubble in DNA?

<p>The separation of DNA strands at points rich in A and T. (A)</p> Signup and view all the answers

Why is the presence of SSB proteins critical during DNA replication?

<p>They prevent DNA strands from reannealing and protect them from nucleases. (C)</p> Signup and view all the answers

Which feature distinguishes Helicase in the DNA replication process?

<p>It requires energy to separate hydrogen bonds. (A)</p> Signup and view all the answers

What role does Etoposide serve in cancer treatment?

<p>It interrupts cancer cell replication by targeting Topoizomerase. (C)</p> Signup and view all the answers

Flashcards

Proofreading by DNA polymerase III

DNA polymerase III uses its 3' to 5' exonuclease domain to cut out the last nucleotide if it was mistakenly added and then replaces it with the correct one

Leading Strand

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

Lagging Strand

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

Primosome

A complex of proteins including Primase that synthesizes RNA primers on the template strand

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Okazaki Fragments

Short fragments of DNA created on the lagging strand, synthesized from an RNA primer to another.

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DNA Polymerase I

A DNA polymerase enzyme with exonuclease activity that removes RNA primers and replaces them with DNA.

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Pseudonucleotides

Drugs that block DNA replication by mimicing nucleotides, but possess a modified sugar structure that DNA polymerases cannot recognize.

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DNA Ligase

An enzyme that connects the ends of Okazaki fragments after the RNA primers are removed.

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5' to 3' Direction of DNA Synthesis

The orientation in which DNA polymerase adds nucleotides, from the 5' end to the 3' end of the new strand.

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Origin of Replication

The site where DNA replication begins, rich in A and T bases.

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Single-Strand Binding Proteins (SSB Proteins)

Proteins that bind to separated DNA strands to prevent them from rejoining and protect them from degradation.

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Helicase

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

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Supercoils

Tightly wound regions of DNA created downstream as Helicase unwinds the helix.

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Topoisomerase

An enzyme that resolves supercoils by temporarily cutting and rejoining DNA strands.

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Primase

An enzyme that creates a short RNA primer, providing a starting point for DNA polymerase.

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Primer

The small RNA strand created by Primase to initiate DNA replication.

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3' to 5' direction

DNA Polymerase reads the template strand in this direction.

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5' to 3' direction

DNA Polymerase builds the new strand in this direction.

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Study Notes

DNA Replication

  • DNA replication starts with separating DNA strands at specific locations (origin points/consensus areas). These locations are rich in adenine (A) and thymine (T) base pairs.
  • Bacterial DNA has one origin point, while eukaryotic DNA has multiple.
  • DNA helicase initially separates the DNA strands, creating a replication bubble.
  • Single-strand binding proteins (SSBs) prevent the separated strands from reannealing.
  • DNA helicase requires a lot of energy to break hydrogen bonds.
  • Topoisomerase enzymes relieve the stress created by unwinding the DNA ahead of the replication fork. There are various types such as Topoisomerase I and Topoisomerase II.
  • Some antibiotics like quinolones target bacterial topoisomerases, leading to DNA damage and cell death.

Initiation of Replication

  • Primase (a DNA-dependent RNA polymerase) creates short RNA primers which provide a 3' hydroxyl group that DNA polymerase requires to start replication.
  • DNA polymerase adds nucleotides to the 3' end of the primer, extending the DNA strand in the 5' to 3' direction.
  • Lagging strand synthesis occurs in short fragments (Okazaki fragments) that are later joined by DNA ligase.

DNA Polymerases (Eukaryotic)

  • There are multiple DNA polymerases in eukaryotic cells, each with specialized functions.
  • Examples include: X-pol (primer), B-pol (repair), and Y-pol (mitochondrial DNA).
  • δ-pol elongates the leading strand and ε-pol is also involved in DNA repair.
  • Some medications target the mitotic spindle to stop cancer cell replication. Examples include vinblastine and vincristine. Others, like Paclitaxel and Docetaxel, hyperstabilize the spindle.

Anti-cancer and Anti-viral Drugs

  • Anti-cancer and anti-viral drugs include analogs of nucleotide bases or altered sugar structures in nucleotides. Examples are didanosine, vidarabine, acyclovir, cytarabine, and zidovudine.
  • These altered nucleotides can interfere with DNA polymerase function, causing replication errors and preventing cell growth and replication.

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Related Documents

DNA Replication PDF

Description

Explore the essential processes of DNA replication, including the roles of enzymes like DNA helicase and primase. Understand differences in replication between bacterial and eukaryotic DNA. Discover how antibiotics can affect bacterial DNA replication.

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