1.3.3 - How DNA works

Question 1

what is conservative replication?

Answer 1

the original double helix remains intact

instructs the formation of a new identical double helix, made completely of new material

Question 2

what is semi-conservative replication?

Answer 2

DNA ‘unzips’ along the hydrogen bonds
new nucleotides align along each strand
each new double helix contains one strand of the original and one new strand

Question 3

how was semi-conservative replication found to be the accepted model of DNA replication?

Answer 3

they used isotopes of Nitrogen to compare the densities of the DNA
the DNA was found to have the density between N15 and N14 meaning it replicates semi-conservatively
(it is a mixture of the original strands and new strands)

Question 4

how does DNA replicate itself?

Answer 4

• DNA helicase separates the two strands of DNA by unzipping along the line of hydrogen bonds + unravelling
• the strands act as templates for the new DNA strands
• exposed bases attract free DNA nucleotides
• new hydrogen bonds are formed between matching base pairs (DNA polymerase and ligase are used)
• two new strands of DNA are produced, identical with the original
• new molecules automatically coil up into a double helix
  (done by formation of weak hydrogen bonds)

Question 5

what does DNA polymerase do?

Answer 5

lines up and catalyses the linking of nucleotides

Question 6

What does DNA ligase do?

Answer 6

catalyses the formation of phosphodiester bonds between the two strands of DNA