Eukaryotic DNA Replication Enzymes

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Questions and Answers

What is the primary function of topoisomerase II during prokaryotic DNA replication?

To introduce positive supercoils

To synthesize new RNA primers

To untangle interconnected daughter DNA (correct)

To connect DNA fragments after replication

Which of the following best describes the action of DNA ligase in the replication process?

It removes RNA primers and replaces them with DNA

It unwinds the DNA helices

It synthesizes new DNA strands ahead of the replication fork

It connects adjacent DNA strands after replication (correct)

How do quinolones and fluoroquinolones affect topoisomerases during DNA replication?

They replace DNA ligase in the replication process

They inhibit the ligase activity of gyrase and topoisomerase IV (correct)

They promote negative supercoiling

They enhance the activity of topoisomerases

Which of the following statements about DNA gyrase is accurate?

It neutralizes positive supercoils introduced during strand unwinding Signup and view all the answers

What enzymatic function is specifically necessary for the initiation of DNA replication?

RNA primer synthesis by primase Signup and view all the answers

Which DNA polymerase is responsible for gap filling in eukaryotic DNA replication?

DNA polymerase δ Signup and view all the answers

In eukaryotic DNA replication, which enzyme is primarily responsible for unwinding the DNA double helix?

MCM Helicase Signup and view all the answers

What is the role of topoisomerases in eukaryotic DNA replication?

To remove supercoils ahead of the replication fork Signup and view all the answers

Which protein complex is responsible for the initiation of replication in eukaryotes?

Orc complex Signup and view all the answers

What enzyme is responsible for the removal of RNA primers during eukaryotic DNA replication?

RNase H Signup and view all the answers

Which type of DNA polymerase is involved in the priming stage of eukaryotic DNA replication?

DNA polymerase α Signup and view all the answers

What is the primary role of single-stranded binding proteins during DNA replication?

To protect unwound DNA strands from degradation Signup and view all the answers

Which of the following enzymes is involved in sealing nicks in the DNA during eukaryotic replication?

DNA ligase Signup and view all the answers

What is the primary role of DNA polymerase III in prokaryotic DNA replication?

To catalyze the addition of nucleotides to the growing DNA strand Signup and view all the answers

What direction does DNA polymerase synthesize new DNA strands?

5' to 3' Signup and view all the answers

Which property of DNA polymerases allows them to remain attached to DNA for extended periods?

Processivity Signup and view all the answers

What role do exonuclease activities of DNA polymerases play during replication?

They remove incorrect nucleotides from the newly synthesized strand Signup and view all the answers

What is the significance of the origin of replication (ori) in bacterial DNA replication?

It is where the DNA double helix unwinds and separates Signup and view all the answers

Which statement about primase activity during DNA replication is true?

Primase is required for DNA synthesis but does not require a pre-existing primer Signup and view all the answers

Which of the following roles do single-stranded binding proteins play during DNA replication?

They stabilize the unwound DNA strands to prevent re-annealing Signup and view all the answers

How do topoisomerases facilitate DNA replication?

By breaking and rejoining DNA strands to relieve torsional strain Signup and view all the answers

What distinguishes DNA polymerases in eukaryotic organisms from those in prokaryotic organisms?

Eukaryotes have multiple types of DNA polymerases with specialized functions Signup and view all the answers

What is a replisome?

Coordinated assembly of various proteins and enzymes that carry out DNA replication. Helicase is a crucial component of the replisome. Signup and view all the answers

what keeps DNA open during replication for prokaryotes and eukaryotes

prokaryotes have ssDNA binding proteins and eukaryotes have replication protein A Signup and view all the answers

what is the sliding clamp?

a ring-shaped protein complex that encircles DNA and holds DNA polymerase in place during replication. By increasing the processivity of DNA polymerase, it ensures efficient and accurate DNA synthesis, playing a vital role in the replication machinery of both prokaryotic and eukaryotic cells. Signup and view all the answers

Study Notes

### Eukaryotic DNA Replication Enzymes

Initiation: Initiator proteins in prokaryotes are replaced with the Origin Recognition Complex (ORC) in eukaryotes.
Unwinding: The prokaryotic Helicase is replaced by MCM Helicase in eukaryotes.
Supercoil Removal: Prokaryotes use Topoisomerase & Gyrase, while eukaryotes use Topoisomerases.
Priming: The prokaryotic Primase is replaced by DNA polymerase α in eukaryotes.
Primary DNA Synthesis: The prokaryotic DNA polymerase III is replaced by DNA polymerase δ (or ε) in eukaryotes.
Primer Removal: In prokaryotes, DNA polymerase I removes primers, while in eukaryotes, RNase H or FEN‐1 performs this function.
Gap Filling: Prokaryotic DNA polymerase I fills gaps, while in eukaryotes, DNA polymerase δ (or ε) takes on this role.
Nick Sealing: Both prokaryotes and eukaryotes utilize DNA Ligase to seal gaps in the DNA strands.

Identifying Structures in a DNA Fork

Direction of fork movement: The fork moves from 5' to 3'.
Leading strand template: The template strand is oriented 3' to 5'
Lagging strand template: The template strand is oriented 5' to 3'.

Important Steps in DNA Replication

Disassembly of replication complexes: This marks the end of the replication process.
RNA primer removal and replacement with DNA: Ensures a continuous DNA strand is formed.
DNA ligase connects adjacent strands: Forms a complete and unbroken DNA molecule.

Prokaryotic Termination of DNA Synthesis

Topoisomerase II untangles interconnected daughter DNA: This resolves any intertwining of the newly replicated DNA strands.

Prokaryotic DNA Gyrase

A Type II topoisomerase that plays a critical role in DNA replication by neutralizing the positive supercoils generated by Helicase.
Relaxes DNA by introducing negative supercoils.
ATP-dependent indicating it requires energy to function.
Acts like a swivel ahead of the active replication fork: This helps manage tension and prevent the DNA from getting tangled.

Inhibition of Prokaryotic Topoisomerase

Quinolones & Fluoroquinolones act as inhibitors of Gyrase and Topoisomerase IV.
These inhibitors block the ligase activity of the enzymes, halting DNA replication.
These drugs are commonly used as antibiotics and are known for their effectiveness against bacterial infections.
Eukaryotic topoisomerase inhibitors are structurally different and are given different names.

The Importance of DNA Replication

Essential for cell division: DNA replication creates a copy of the genome before a cell divides.

Prokaryotic DNA Replication: General Features

Replication precedes cell division.
DNA replication creates a complete and faithful copy of the cell's chromosomes.
The process ensures that each new daughter cell receives a complete copy of the genetic information.

Prokaryotic DNA Polymerase III

Different types of polymerase exist for tasks including genome replication, repair, and telomere replication.
The primary polymerase in prokaryotic DNA replication.
Composed of multiple subunits with specialized functions including proofreading to maintain replication accuracy.
Displays high processivity: Able to remain attached to DNA for extended stretches without detaching.
Moves along the DNA template strand, adding complementary bases. This process builds a new DNA strand.
Catalyzes the addition of nucleotides to the 3' OH end of the growing strand. This ensures that the new strand is synthesized in the 5' to 3' direction.
Proofreading activity: Identifies and removes incorrectly incorporated nucleotides to ensure high fidelity of replication.

DNA Synthesis by DNA Polymerases

The synthesised new strand grows in the 5' to 3' direction.
DNA polymerase requires both a template and a primer to function. The template provides the sequence information, and the primer provides a free 3' OH group for the addition of the first nucleotide.

Prokaryotic DNA Replication: Initiation

Replication starts at specific sites on the DNA molecule known as ori (origin) of replication.
These regions contain specific sequences recognized by replication proteins, directing the initiation process.
Bacteria have a single ori per chromosome, while eukaryotes have multiple origins.
These regions are where unwinding and separation of the double-stranded DNA (dsDNA) occurs.
The ori directs the assembly of replication machinery.
In bacteria, sequences near the ori play a role in distributing replicated chromosomes to daughter cells.

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Description

This quiz covers the various enzymes involved in eukaryotic DNA replication, comparing them to their prokaryotic counterparts. Learn about the roles of enzymes such as the Origin Recognition Complex, MCM Helicase, and DNA polymerases. Test your knowledge on the differences and similarities between prokaryotic and eukaryotic DNA replication processes.