What did the fragmentation, or dispersive, theory of DNA replication propose?

The dispersive theory proposed that the parent molecule breaks into pieces that are copied and reassembled. Each strand of the new molecules would be a patchwork of old and new sections.

What is the role of DNA helicase in replication?

DNA helicase unwinds the double helix. The enzyme breaks the hydrogen bonds between complementary bases, so the two strands separate and expose their bases.

How are new nucleotides lined up against a template strand?

Free DNA nucleotides are attracted to the exposed bases on each template strand. Each pairs with its complementary base, adenine with thymine and cytosine with guanine.

CCEA A-Level Life and Health Sciences 0008

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Genetics, Stem Cell Research and Cloning

DNA replication and the Meselson–Stahl experiment

3 things to know
A2 5

Overview

Conservative, semi-conservative and dispersive theories, the roles of helicase and DNA polymerase, and how Meselson and Stahl's 1958 nitrogen isotope experiment supported semi-conservative replication.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why must DNA be copied exactly before a cell divides?

Key term

What did the conservative theory of DNA replication propose?

Key term

What did the semi-conservative theory of DNA replication propose?

Questions from this subtopic

Each one with the model answer underneath.

1
Why must DNA be copied exactly before a cell divides?
Model answer
Each daughter cell needs a complete, identical set of genetic information. Errors in copying would pass mutations to the daughter cells.
2
What did the conservative theory of DNA replication propose?
Model answer
The conservative theory proposed that the original double helix stays intact. The copy would be a completely new double helix made of two new strands.
3
What did the semi-conservative theory of DNA replication propose?
Model answer
The semi-conservative theory proposed that the two strands separate and each acts as a template. Every new molecule contains one original strand and one new strand.
4
What did the fragmentation, or dispersive, theory of DNA replication propose?
Model answer
The dispersive theory proposed that the parent molecule breaks into pieces that are copied and reassembled. Each strand of the new molecules would be a patchwork of old and new sections.
5
What is the role of DNA helicase in replication?
Model answer
DNA helicase unwinds the double helix. The enzyme breaks the hydrogen bonds between complementary bases, so the two strands separate and expose their bases.
6
How are new nucleotides lined up against a template strand?
Model answer
Free DNA nucleotides are attracted to the exposed bases on each template strand. Each pairs with its complementary base, adenine with thymine and cytosine with guanine.

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