DNA Replication Overview

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Questions and Answers

What is the main role of Single-Strand Binding proteins (SSB) during the DNA replication process?

To create replication bubbles.

To prevent DNA strands from reannealing. (correct)

To synthesize new DNA strands.

To break hydrogen bonds between base pairs.

Which enzyme is primarily responsible for unwinding the DNA double helix during replication?

Primase

DNA-A protein

Topoizomerase

Helicase (correct)

What best describes the function of Topoizomerase during DNA replication?

It synthesizes RNA primers.

It synthesizes nucleotides for new DNA strands.

It resolves supercoiling in DNA. (correct)

It separates DNA strands at the point of origin.

What is the consequence of Quinolones on bacterial DNA replication?

They lead to the disintegration of DNA. Signup and view all the answers

What role does Primase play in the process of DNA replication?

It creates RNA primers for DNA synthesis. Signup and view all the answers

Which statement correctly describes the activity of DNA polymerase?

It synthesizes DNA in the 5' to 3' direction. Signup and view all the answers

How does Topoizomerase 2 differ from other types of Topoizomerases?

It has two nuclease domains. Signup and view all the answers

What initiates the formation of the replication bubble in DNA replication?

Separation of DNA strands at points of origin. Signup and view all the answers

What is the role of the ligase domain in Topoizomerase?

It repairs cuts in the DNA strand. Signup and view all the answers

Which statement about the leading strand is correct?

It is synthesized continuously towards the replication fork. Signup and view all the answers

What major role does DNA polymerase I play during DNA replication on the lagging strand?

It replaces RNA primers with DNA nucleotides. Signup and view all the answers

What are Okazaki fragments?

Short segments of DNA synthesized on the lagging strand. Signup and view all the answers

Which enzyme is responsible for the synthesis of RNA primers?

Primase Signup and view all the answers

What is the consequence of incorporating pseudonucleotides into the DNA strands?

Termination of further DNA chain elongation. Signup and view all the answers

How does the exonuclease domain of DNA polymerase I differ from that of DNA polymerase III?

It removes RNA phosphodiester bonds from the primer. Signup and view all the answers

What function does DNA ligase perform during DNA replication?

It joins Okazaki fragments together. Signup and view all the answers

In which direction does DNA polymerase proofread new DNA strands?

3' to 5' Signup and view all the answers

Which term describes the complex involved in the synthesis of RNA primers?

Primosome Signup and view all the answers

The direction of synthesis for the lagging strand is away from what structure?

Replication fork Signup and view all the answers

Study Notes

DNA Replication

Replication begins by separating DNA strands at specific locations, rich in A-T base pairs, called origins or consensus areas. Bacterial DNA has one origin, while others have multiple.
DNA-A protein initially separates DNA strands, creating a replication bubble.
Single-strand binding proteins (SSB proteins) bind to separated DNA strands, preventing re-annealing and protecting them from damage.
Helicase unwinds the DNA double helix, requiring a significant amount of energy. This creates supercoils in the DNA ahead of the replication fork.
Topoisomerases resolve these supercoils, using a double-function enzymatic process.
Topoisomerases have two domains: a nuclease domain (that cuts a DNA strand), and a ligase domain (that rejoins DNA strands). Several types exist with varying roles, for example in preventing tangling.

DNA Replication Enzymes

Primase (DNA-dependent RNA polymerase) synthesizes RNA primers, providing a starting point for DNA polymerase.
DNA polymerase is responsible for building new DNA strands by adding nucleotides to the 3' end of the growing chain.
Polymerase reads the template DNA in the 3' to 5' direction but synthesizes new DNA strands in the 5' to 3' direction (so, the newly made strand is anti-parallel to the template strand), and proofreads its work.
DNA polymerase has an exonuclease domain that removes incorrect nucleotides if a mistake is found.
Leading strand synthesis occurs continuously, while lagging strand synthesis occurs in short fragments (Okazaki fragments) that are subsequently joined by DNA ligase.
Primosomes are complexes of primase and other proteins that synthesize RNA primers on the lagging strand.

DNA Replication Errors and Inhibitors

Pseudonucleotides (nucleoside analogs) lack a hydroxyl group on carbon 3' and can block further nucleotide addition
Some drugs, like Didanosine, Vidarabine, Acyclovir, Cytarabine, and Zidovudine, are nucleoside analogs that become incorporated into the growing DNA chain, causing replication errors and inhibiting further replication.
Some antibiotics, like Quinolones, interfere with Topoisomerases to prevent DNA replication.
Cancer drugs, like Etoposide and Teniposide, target human topoisomerases.
Vincristine and Vinblastine affect the mitotic spindle, inhibiting cell division.
Paclitaxel and Docetaxel overstabilize the mitotic spindle.

DNA Polymerases

There are different types of DNA polymerase enzymes in eukaryotes with specialized functions (X-pol, B-pol, Y-pol, 8-pol, and E-pol.) some similar to prokaryotes. Different DNA polymerases are specialized in different tasks - for example replicating leading and lagging strands, repair of DNA.
Not all prokaryotic enzymes are the same as eukaryotic ones.

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Description

This quiz covers the essential processes involved in DNA replication, including the roles of various enzymes and proteins. Learn about the separation of DNA strands, the function of helicase, and the importance of topoisomerases. Perfect for students studying molecular biology!