DNA replication

Question 1

describe DNA replication?

Answer 1

1. DNA helicase ‘unzips’ the double helix of DNA by breaking the hydrogen bonds between the complementary bases. the two strands unwind. each strand can be used as a template
2. free DNA nucleotides align next to their complementary bases on each strand and bond via hydrogen bonds
3. DNA polymerase joins these nucleotides via phosphodiester bonds to make them into a strand
4. 2 identical DNA molecules are produced. both contains one new strand and one original strand (semi-conservative replication)

Question 2

When does DNA replication occur?

Answer 2

Just before cell division

Question 3

Why does DNA need to be replicated?

Answer 3

So that the daughter cells are genetically identical to the original cell

Question 4

How Do we know DNA replicates

Answer 4

Meselson + stahl Experiment

Question 5

What is semi conservative replication?

Answer 5

When the DNA strand contains one new strand and one old strand

Question 6

Why does DNA polymerase work in opposite directions for each strand?

Answer 6

Because nucleotides are opposite way round for each strand (anti parallel)

Question 7

Describe Meselson and Stahls experiment

Answer 7

1. Cultured E.Coli bacteria in medium containing an isotope of Nitrogen (N^15), therefore nucleotides would contain the isotope and be heavier
2. They changed the bacteria to a medium containing a lighter isotope (N^14), so new nucleotides were lighter
3. After one replication DNA was extracted and centrifuged

After one gen: single band of medium density

Sec gen: one light and one intermediate band (half N^15, half N^14)