DNA replication

Question 1

What is DNA replication?

Answer 1

During cell division, DNA must replicate so that each daughter cell receives an exact copy of the genetic information
Takes place in the nucleus during interphase

Question 2

Name the enzyme that separates the strand of the double helix

Answer 2

DNA helicase

Question 3

Name the enzyme which catalyses the addition of new nucleotides to the new growing ‘daughter’ strand of DNA

Answer 3

DNA polymerase

Question 4

What is the name given to the manner in which DNA is replicated?

Answer 4

Semi conservative

Question 5

What do each of the separated ‘parent’ strands provide?

Answer 5

A template for the formation of a new strand

Question 6

In what direction does DNA replication occur?

Answer 6

5 prime to 3 prime direction

Question 7

What is meant by semi-conservative replication?

Answer 7

Each new DNA molecule is made up one old ‘conserved’ strand and one new one

Question 8

Describe the process of DNA replication

Answer 8

DNA unwinds
Hydrogen bonds holding complementary base pairs break, catalysed by DNA helicase and the 2 strand separate
Each DNA strand acts as a template
Free DNA nucleotides align opposite their complementary bases
DNA polymerase catalyses the condensation reaction between 2 DNA nucleotides from the 5 prime to the 3 prime end of the chain
Each new DNA molecule is made from one original template strand and one newly replicated strand - known as semi-conservative replication

Question 9

What are the 3 theories of DNA replication?

Answer 9

Conservative
Semi-conservative
Dispersive

Question 10

What is the conservative DNA replication theory?

Answer 10

Parental double helix remains intact, completely conserved & a whole new DNA molecule is made

Question 11

What is the semi conservative DNA replication theory?

Answer 11

Each strand in the parental double helix acts as a template to synthesise a new polynucleotide strand
Each new DNA molecule contains one template strand and one newly replicated strand

Question 12

What is the dispersive DNA replication theory?

Answer 12

Each new DNA molecule contains fragments of the parental double helix and newly synthesises DNA

Question 13

What did Meselson and Stahl show experimentally?

Answer 13

Used the bacteria Escherichia coli - easy culture
The DNA is not contained within a nucleus bound by a nuclear membrane
Grew it with different isotopes of nitrogen

Question 14

Describe the Meselson-Stahl experiment

Answer 14

E-coli was grown in a medium containing amino acids made with the heavy isotopes 15N
Bacteria produced nucleotides containing 15N
All the bacteria’s DNA contained this heavy isotope
DNA was extracted and the suspension then centrifuged
Bacteria was washed and then transferred to a medium containing amino acids with the lighter isotope 14N and allowed to divide once
SNA was extracted and the suspension then centrifuged
Bacteria were allowed divide again (2 generations) on the 14N medium
DNA was again centrifuged