DNA Replication & Repair: Semiconservative Method, Enzymes, and Error Correction

What is semiconservative replication?

A method of DNA replication where each new double-stranded DNA molecule contains one parent strand and one newly synthesized strand.

Who conducted the experiment demonstrating semiconservative replication?

Matthew Meselson and Franklin Stahl in 1958.

What isotope was used to label the parent DNA in Meselson and Stahl's experiment?

Isotope 15^N.

What happens to DNA during the first round of replication in Meselson and Stahl's experiment?

A new band forms at a density that matches the hybrid DNA, indicating semiconservative replication.

What is the role of helicase in DNA replication?

Helicase unwinds the DNA strands by breaking hydrogen bonds between base pairs.

What structure is formed when the DNA strands are separated during replication?

A Y-structure called the replication fork.

What is the purpose of topoisomerases during DNA replication?

To relieve tension by cutting and rejoining DNA strands near the replication fork.

What do single-strand binding proteins (SSBs) do?

They stabilize and keep the separated DNA strands apart during replication.

What are RNA primers and their role in DNA replication?

RNA primers are short RNA sequences added to the naked strands to initiate the synthesis of new DNA strands.

What enzyme is responsible for adding new nucleotides during DNA replication?

DNA polymerases.

What is the leading strand in DNA replication?

The strand that is synthesized continuously towards the replication fork.

What are Okazaki fragments?

Short segments of DNA synthesized on the lagging strand during replication.

What is the function of DNA polymerase I?

To remove RNA primers and replace them with DNA nucleotides.

What enzyme catalyzes the joining of Okazaki fragments?

DNA ligase.

How do DNA polymerases correct errors during replication?

They proofread and correct base-pair mismatches by backing up and fixing incorrect bases.

What is the average error rate of DNA replication?

One error for every million base pairs.

What are DNA repair complexes composed of?

Proteins and enzymes, including DNA polymerase I and II.

What does DNA polymerase II do?

It slowly repairs damage to DNA between replication events.

What is the consequence of a thymine-cytosine base pair mismatch?

It cannot form hydrogen bonds, leading to instability in the DNA strand.

What is the role of special DNA repair complexes?

To locate and correct distortions in DNA strands that may have been missed during replication.