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aqa a level biology (congito) > 2.2 — DNA replication > Flashcards

2.2 — DNA replication Flashcards

1
Q

what process in DNA copied by?

A

semi-conservative replication

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2
Q

what does semi-conservative replication of DNA produce?

A

DNA molecules consisting of one original DNA strand and one newly synthesised DNA strand

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3
Q

what are the stages of semi-conservative replication in DNA?

A
  1. DNA molecule is ready to be replicated
  2. the enzyme DNA helicase breaks down hydrogen between complimentary bases. this unwinds the double helix and separates the strands.
  3. each strand acts as a templates as free nucleotides attract to their complimentary bases. (A+T, C+G)
  4. the enzyme DNA polymerase joins the free nucleotides together via condensation reaction in the 5’ to 3’ direction. this forms phosphodiester bonds to create the sugar-phosphate backbone of the new DNA strand
  5. two identical copies of DNA are made. each copy is made up of one of the original (template) strands and one newly synthesised DNA strand
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4
Q

what enzyme breaks the hydrogen bonds between the complimentary bases?

A

DNA helicase

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5
Q

what does DNA helicase breaking the DNA strands’ hydrogen bonds allow?

A

allows the double helix to unwind and separates the strands

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6
Q

what does the template strands in semi-conservative replication attract?

A

complimentary bases that are free floating nucleotides

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7
Q

what does the enzyme DNA polymerase do in semi-conservative replication?

A

it joins the free floating nucleotides together via condensation reaction, allowing a sugar-phosphate backbone to form on the new DNA strand

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8
Q

what direction does DNA polymerase join free nucleotides together?

A

5’ to 3’

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9
Q

what type of DNA strands are made from semi-conservative replication?

A

two identical strands

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10
Q

what are the stages in conservative DNA replication?

A
  1. the original DNA molecule stays intact while a completely new copy is built
  2. after a single replication, one molecule has two original strands and the other has two new strands
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11
Q

what are the main features of semi-conservative replication in DNA?

A
  1. the original DNA splits and each strand acts as a template for a new strand
  2. after a single replication, each model has one original strand and one new strand
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12
Q

what three principles was the Meselson-Stahl experiment based on?

A
  1. DNA contains nitrogen
  2. two different nitrogen isotopes can be used to mark DNA strands and track them during replication; 14N (lighter) and 15N (heavier)
  3. bacteria use nitrogen from their surroundings to build new DNA molecules
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13
Q

what was the experimental process for the Meselson-Stahl experiment?

A
  1. bacteria were grown in a medium containing 15N, so all of their DNA was ‘heavy’
  2. the bacteria were transferred to a medium with 14N for one round of replication, so the lighter nitrogen was incorporated into any new DNA strands made
  3. the DNA was extracted and centrifuged
  4. steps 2-3 were repeated for another round of replication
  5. the distribution of heavy and light DNA was analysed to track how the DNA was replicating:
  • the heavier bands sink lower in the test tube
  • the intermediate bands, made from the DNA which was one light and one heavy strand, are in the middle of the test tube
  • the lighter bands are higher up in the test tube
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14
Q

what does the Meselson-Stahl experiment show?

A

that DNA replicates through a semi-conservative process

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15
Q

what occurs in the first replication in the Meselson-Stahl experiment?

A
  1. the original, heavy DNA strands separate
  2. each heavy strand acts as a template for a new complimentary strand
  3. new, light strands form alongside the original strands
  4. each resulting DNA molecule consists of one old, heavy strand and one new, light strand
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16
Q

what occurs in the second replication in the Meselson-Stahl experiment?

A
  1. both original strands and the new strands act as templates
  2. new, light strands form alongside all four templates
  3. half the resulting have one original, heavy strand and one new, light strand
  4. the other half are completely made up of light strands

aqa a level biology (congito) (40 decks)

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