2.2 - DNA replication Flashcards

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1
Q

What are the 2 main stages of cell division

A
  • nuclear division: process by which the nucleus divides (mitosis/meiosis)
  • cytokinesis: follows nuclear division, the process by which the whole cell divides
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2
Q

What must be done before a nucleus divides and why

A
  • DNA must be replicated
  • ensures all daughter cells have the genetic info in order to produce the enzymes and other proteins they’ll need
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3
Q

What model is used to describe the process of DNA replication

A

Semi-conservative model

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4
Q

What are the requirements are needed for semi-conservative replication to take place

A
  • the 4 types of nucleotide (with their bases of AGCT) much be present
  • both strands of DNA act as a template for the attachment of these nucleotides
  • the enzyme DNA polymerase
  • A source of chemical energy is required to drive this process
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5
Q

What are the 4 steps to the process of semi-conservative replication

A

1) the enzyme (DNA helicase) breaks the hydrogen bonds between bases on the two polynucleotide DNA strands.
—> this makes the helix unwind to form 2 single strands
2) each original single strand acts as a template for a new strand. Free floating DNA nucleotides are attracted to their complementary exposed bases on each original template strand (complementary base pairing)
—>A with T and C with G
3) DNA polymerase joins nucleotides to each other on the new strand forming phosphodiester bonds to create the phosphodiester backbone
—> hydrogen bonds form between the bases on the original and new strands
4) Each new DNA molecule contains one strand from the original DNA molecule and one new strand

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6
Q

What is the role of DNA polymerase in semi-conservative replication

A
  • catalyses the joining of the nucleotides
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7
Q

If the bases on a portion of the original strand of DNA are ATGCTACG, determine the equivalent sequence of bases on the Newley formed strand

A

TACGATGC

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8
Q

Explain why the process of DNA replication is described as semi-conservative

A

Because half the original DNA is built into the new DNA strand

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9
Q

If an inhibitor of DNA polymerase were introduced into cell, explain what the effect would be on DNA replication

A
  • the linking together of the new nucleotides couldn’t take place
  • while the nucleotides would match up to their complementary nucleotides on the original DNA strand
  • they wouldn’t join together to form a new strand
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10
Q

Who came up with the theory of semi-conservative DNA replication

A

Watson and Crick

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11
Q

Who validated the theory of semi-conservative replication

A
  • Meselson and Stahl’s experiments
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12
Q

What was the difference between semi-conservative and conservative replication

A
  • conservative: original DNA strands would stay together, and new DNA molecules would obtain two new strands
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13
Q

What was concluded from Meselson and Stahl’s experiments, and what did this lead to

A
  • DNA settled out in the middle = the DNA contained a mixture of heavy and light nitrogen = the bacterial DNA had replicated semi-conservatively in the light nitrogen
  • their experiment = confirms DNA replication in bacteria was semi-conservative
  • leads to = other scientists carry out experiments to see if t was the case in all living tings
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14
Q

What are isotopes

A

Different forms of the same element

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15
Q

How did Meselson and Stahl’s experiment work

A
  • 2 samples of bacteria are grown — 1 in a nutrient broth containing light nitrogen, and 1 in heavy nitrogen
  • as bacteria reproduced = they took up nitrogen from broth to help make nucleotides for new DNA = so nitrogen gradually became part of the bacteria’s DNA
  • sample of DNA taken from each batch of bacteria, then spun in a centrifuge = DNA from heavy nitrogen bacteria settled lower down the centrifuge tube than the DNA from the light nitrogen bacteria – because it’s heavier
  • heavy nitrogen bacteria = taken out of broth, put in light nitrogen broth = after 1 round of DNA replication, sample taken and spun in centrifuge again
  • if replication conservative = original heavy DNA would still be together = settle at bottom whilst light at the top
  • if replication semi-conservative = DNA would settle between where heavy and light nitrogen containing DNA settles (because contains: 1 strand of old DNA containing heavy nitrogen, and 1 strand of new DNA containing light nitrogen)
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16
Q

Name the part of the DNA molecule that contains nitrogen

A

The organic bases (adenine, guanine, cytosine and thymine)

17
Q

Explain why, after 1 generation, all the DNA is made up of an equal mixture of 14N (the number on top right if N) and 15N

A
  • Each DNA molecule is made up of 1 strand containing 15N (the original strand) and one strand containing 14N (the new strand)
  • therefore the replication was semi-conservative
18
Q

What were the 3 facts that Meselson and Stahl worked on

A
  • All bases in DNA contain nitrogen
  • Nitrogen has 2 forms: the lighter nitrogen (14N) and THE ISOTOPE (15N), which is heavier
  • Bacteria will incorporate nitrogen from their growing medium into any new DNA they make