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Flashcards in 2: DNA Replication Deck (10)
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1
Q

What did Crick and Watson’s model suggest?

A

a method of copying called semi-conservative replication

2
Q

Outline the process of semi-conservative replication.

A
  • two strands of DNA molecule are separated by breaking h-bonds between their bases
  • new polymers of nucleotides are assembled on each of the two single strands
3
Q

Define ‘template strand’.

A

a strand of DNA on which a new strand is assembled

4
Q

What is the significance of complementary base pairing in DNA replication?

A

it means that each new strand has the same base sequence as the old strand that was separated from the template strand

replicates = identical

5
Q

What is the result of semi-conservative replication?

A

both DNA molecules have one new strand and one strand conserved from parent molecule

6
Q

DNA replication is semi-conservative. What two alternative theories were suggested?

A
  1. conservative replication - both strands of parent DNA remain together and another molecule is produced with 2 new strands
  2. dispersive replication - every molecule produced by DNA replication has a mixture of old and new sections in both of its strands
7
Q

What did Meselson and Stahl do (re DNA replication)?

A

published strong evidence for semi-conservative replication

8
Q

Describe Meselson and Stahl’s experiment on DNA replication. (p29)

A
  1. cultured many generations of E.coli bacteria in medium of ^15 N = nitrogen in bases of all bacteria was ^15 N
  2. transferred bacteria to less dense ^14 N medium
  3. solution of caesium chloride spun in ultracentrifuge at 45,000 revolutions per minute for 24 hours
  4. caesium ions are heavy so tend to sink, establishing a gradient (greatest caesium concentration therefore density at bottom)
  5. any substance centrifuged with caesium becomes concentrated at its level of density
  6. M+S spun samples of DNA collected from bacterial culture at diff times after transfer to ^14 N medium
  7. DNA shows up as dark band in UV light
  8. after one generation (G1), DNA = intermediate density between ^15 N and ^14 N, as expected with one old and one new strand
  9. G2: two equal bands, one still at ^15 N/ ^14 N and one at ^14 N
  10. in following generations less dense ^14 N band became stronger and ^15 N/ ^14 N band became weaker.
9
Q

Describe stages of DNA replication.

A

Stage 1: helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds

Stage 2: DNA polymerase links nucleotides together to form new strands, using pre-existing strands as templates

Stage 3: daughter DNA molecules each rewind into double helix

10
Q

Why are the two daughter DNA molecules in DNA replication identical in base sequence to one another and to the parent molecule?

A

complementary base pairing:
- adenine will only bond with thymine
- cytosine will only bond with guanine-
= each new strands is complementary to the template strand (on which it was made) and identical to the other template strand