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Grade 12 Biology > DNA replication > Flashcards

DNA replication Flashcards

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1
Q

what is the big idea of DNA replication?

A

DNA replication copies the entire chromosome and occurs during the S-phase (synthesis) of the cell cycle

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2
Q

what does it mean by replication is semi-conservative?

A

it uses an existing parent
strand as the template

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3
Q

Who are the people you know in timeline order?

A

Levene
Chargaff
Franklin & Wilkins
Pauling
Watson & Crick

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4
Q

what did Phoebus Levene determine correctly about DNA

A
  • DNA is made up of chains of nucleotides
  • a nucleotide is a phosphate linked to a sugar linked to one of four nitrogenous bases
  • nucleotides link in series phosphate to sugar
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5
Q

What did Phoebus Levene get wrong about DNA?

A

the tetranucleotide hypothesis, which is the idea of a repeating tetramer, order of bases exist in a fixed pretitive sequence, thus all bases appear in equal ratio

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6
Q

What did Erqin Chargaff discover about DNA?

A

isolated DNA from different organisms and measured numbers of each base present and found the number of A=T and the number of C=G

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7
Q

What did Linus Pauling propose? Right or wrong?

A

proposed the alpha helix secondary structure in proteins, but made it the idea of a triple helix which was wrong

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8
Q

what else did Linus Pauling get wrong?

A
  • phosphate groups were shown as neutral molecules
  • phosphates organized in the core for the helix negative charges on oxygen would repel
  • bases facing outwards
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9
Q

What did Rosalind Franklin & Maurice WIlkins do?

A

x-ray diffraction of crystalline DNA fiber

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10
Q

what id x-ray crystallography?

A

a physics approach to examining biological molecules where a pure crystallized sample of the molecule is isolated, Xrays bombard the crystal sample and refract the rays in multiple directions and the diffraction pattern is analyzed to determine the moldecule’s 3D structure

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11
Q

what did the X-ray ‘expose’

A
  • a double helix structure
  • with a backbone of alternating phosphate and sugars
  • nitrogenous bases are in the middle of the molecule
  • bases are at right angles to the backbone
  • molecule is a uniform helix with consistency in helical dimensions
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12
Q

what are the 4 measurements the x-ray interpretation of DNA was able to yield?

A

diameter
- distance between one helical turn
- distance between one stacked base pair
- angle of helical turns

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13
Q

what did James Watson and Francis Crick find?

A
  • determined rules for base pairing, hydrogen bonding between AT, GC and the width of a purine and pyrimidine pair
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14
Q

What is Chargaff’s ratio?

A

the idea that the ratio of AT is 1:1 and the ratio of CG is also 1:1

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15
Q

How does Chargaff’s ratio dispute Levene’s tetranucleotide hypothesis

A

Leven’s idea was that all bases repeat equally as 1 of each base is in the tetranucleotide. But Chargaff found that there were different ratios of C to T so it was wrong

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16
Q

Describe the error in Pailing’s triple helix model

A
  • phosphate groups were shown as neutral
  • phosphates were in the core of the helix as the negative charges on the oxygen would repel
  • bases faced outwards
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17
Q

what technique that Franklin and Wilkins used in determining the DNA structure

A

x-ray diffraction of crystalline DNA fiber

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18
Q

what are the three methods of DNA replication?

A

conservative, semi-conservative and dispersive

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19
Q

describe the conservative DNA replication model

A

the parental double helix remains intact and an all new copy is made

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20
Q

describe the semi-conservative DNA replication model

A

the two strands of the parental molecule separate and each functions as a template for synthesis of a new complementary strand

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21
Q

describe the dispersive DNA model

A

each strand of both daughter molecules contains a mixture of old and newly synthesized parts

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22
Q

What was the first step of Meselson and Stahl experiment?

A

Grew E.Coli cells in heavy nitrogen. centrifuge the DNA - it shows up heavy as DNA contains nitrogen atoms.

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23
Q

What was the second step of the Meselson & Stahl Experiment

A

transfer the E.Coli cells into a medium with light nitrogen (N14) where they went 1 round of replication, were centrifuged again

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24
Q

What was the third step of the Meselson & Stahl Experiment

A

second round of replication in light medium the centrifuged

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25
Q

if DNA underwent conservative replication, what can be expected after the second step?

A

2 bands

26
Q

if DNA underwent semi-conservative replication, what can be expected after the second step?

A

1 band

27
Q

if DNA underwent dispersive replication, what can be expected after the second step?

A

1 band

28
Q

what did meselson and Stahl observe after the second step?

A

1 band

29
Q

if DNA underwent conservative replication, what can be expected after the third step?

A

2 bands

30
Q

if DNA underwent semi-conservative replication, what can be expected after the third step?

A

2 bands

31
Q

if DNA underwent dispersive replication, what can be expected after the third step?

A

1 band

32
Q

What did Meselson and Stahl observe after the third step

A

2 bands relatively closer together than compared to the conservative ( + conservative already disproven)

33
Q

how does DNA replication initiation differ between prokaryotes and eukaryotes

A

prokaryotes: replication begins at one fixed origina -> bidirectional until all DNA is replicated

eukaryotes: multiple origins of replication

34
Q

ori

A

origins of replication

sites on DNA where replication begins

contains specific sequence recognized by replcation machinery (enzymes)

often high in A-T base pairs

35
Q

describe replication initiation

A

origin sites are separated and separate outwards forming bubbles with replication forks at each end. Separates until there are two daughter DNA molecules

36
Q

primer

A

a short segment of RNA needed to initiate DNA replication

37
Q

why is priming needed?

A

RNA polymerase and DNA polymerase are different - have different abilities:

RNAP can start a new chain without an existing end all required is a template

DNAP can only add nucleotides to the end of an existing chain

38
Q

primase

A

and RNA polymerase (RNAP) which synthesizes the primer by adding ribonucleotides that are complementary to the DNA template

39
Q

polymerase

A

enzyme that makes polymers

40
Q

helicase

A

enzyme that disrupts H bonds between two strands of DNA to separate the template DNA strands at the replication fork

41
Q

single strand bikind proteins (SSBPs)

A

proteins that bind to unwound single stranded regions of DNA to keep the template strands apart during replication

42
Q

topoisomers/topoisomerase

A

enzymes that can brek bonds in DNA and the reform the bonds - can release the twists made in DNA replication like DNA gyrase

43
Q

DNA polymerase

A

enzyme which synthesizes nucleotide chains

44
Q

how do the roles of DNAP I and DNAP III differ?

A

DNAP III catalyzes the elongation of DNA molecules by adding nucleotides to the 3’ end of a pre-existing nucleotide whereas DNAP I replaces the RNA primer with DNA complementary to the template

summar:
DNAP III elogates DNA strand

DNAP I replaces RNA with DNA

45
Q

where are DNAP I and II found?

A

eukaryotes

46
Q

What is the problem at the replication fork caused by the antiparallel nature of DNA

A

one parental strand has its 3’ end while the other has 5’ end at the fork but DNA synthesis can only proceed in a 5’ to 3’ direction to DNA before the 5’ end aren’t synthesized

47
Q

describe leading strand

A

synthesized continuously and polymerizes int he same direction as the replication fork

48
Q

Describe the lagging strand

A

synthesized in short, discontinuous segment of 1000 to 2000 nucleotides called Okazaki fragments

polymerization is in the opposite direction of the replication fork

49
Q

okazaki fragments

A

the discontinuous segments of DNA on the lagging strand

50
Q

name and describe the enzymes on the lagging strand

A

DNAP III synthesizes DNA

DNAP I replaces the RNA primer with DNA complementary to the template

DNA ligase joins broken pirces of DNA by catalyzing the formation of phosphodiester bonds

51
Q

When does DNA replication reach termination for prokaryotes and eukaryotes?

A

for prokaryotes: reaches the end of the chromosome

for eukaryotes: replication bubble or fork meets another replication bubble or fork

52
Q

whats the replication problem at the ends of linear DNA

A

DNA gets progressively shorter with each round of replication

53
Q

what is a telomere and its purpose

A

it protects the chromosomes from being eroded, serves as a protective cap to prevent unwinding

54
Q

telomere structure

A

consists of multiple repeats of short genetic sequence in humans TTAGGG at the ends of eukaryotic chromosomes that are noncoding

55
Q

cellular aging - the two types and their name

A

senescence - where cells stop growing and dividing

OR

apoptosis - programmed self-destruction

56
Q

telomerase + its mechanism

A

enzyme responsible for adding telomeres to chromosomes extends the chain by reverse transcribing off its internal RNA template (repeats) binds to 3’ end of parental strand

57
Q

ribonucleoprotein

A

an enzyme that contains RNA and protein, in humans has an RNA component that contains the internal sequence AAUCCC

58
Q

reverse transcriptase

A

synthesis of complementary DNA from an RNA template, extends the 3’ end of the chromosome

59
Q

what happens if telomere is not long enough

A

conding DNA gets damaged

60
Q

what cell types have telomerase activity

A

germ line cells
cancer cells

61
Q
A

Grade 12 Biology (22 decks)

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