3.1.5.2 DNA replication

Who invented semi conservative model?

Meselson & Stahl

What did they initially believe DNA was replicated like?

Semiconservative replication

Conservative application

What did experiment include?

The new nitrogenous spaces they grew N¹⁵ DNA in N¹⁵ mediums and the new DNA in N¹⁴ mediums later on

Difference between N¹⁵ and N¹⁴ DNA

N¹⁵ DNA is heavier

Why did DNA strands look like this in test tube?

DNA replication is SEMI CONSERVATIVE

•This means that each strand acts as a template

•And that the new double helix (daughter DNA) is made from one old strand and one new strand of DNA

Centrifuge function

To separate DNA according to its density

Where does DNA replication occur?

Interphase

How does DNA replication occur?

DNA replication is SEMI CONSERVATIVE

•This means that each strand acts as a template

•And that the new double helix (daughter DNA) is made from one old strand and one new strand of DNA

Describe how DNA is replicated.

1) DNA helicase separates polynucleotide strands unwinding double helix and breaks the H-bonds between bases

2)Both strands act as template;

3) Free nucleotides attach to the templates by Complementary base pairing (A with T and G with C BUT U MUST WRITE THEM OUT)

4) DNA polymerase catalyses condensation reaction joining the new adjacent nucleotides on new strand together forming phosphodiester bonds;

5) H-bonds reform between the strands;

6) New DNA molecules contain one old strand and one new strand

Why is DNA unwound like this?

Mutations are more likely to occur if bases are fully exposed

Significance of weak H bonds between base pairs in semi-conservative replication

Hydrogen bonds between base pairs are easy to break so good for separating strands

Significance of 2 strands in semi-conservative replication

So both can act as template

Significance of complementary base pairing in semi-conservative replication

Allows for accurate replication