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Molecular Biology and Genetics > The Watson and Crick model of DNA > Flashcards

The Watson and Crick model of DNA Flashcards

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1
Q

Of what does DNA consist?

A

A linear chain of Adenine(A), Cytosine (C), Guanine (G) and Thymine (T) subunits = bases.

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2
Q

How many types of bases exist?

A

2.

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3
Q

Which are the 2 types of bases?

A

Purines (A, G).

Pyrimidines (C, T and U).

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4
Q

What is the characteristic of Purine bases?

A

Double-ring structure.

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5
Q

What is the characteristic of Pyrimidine bases?

A

Single-ring structure.

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6
Q

Of what are bases a part?

A

Larger subunits = nucleosides and nucleotides.

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7
Q

What is the nucleotide monophosphate?

A

Building-block of DNA polymer.

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8
Q

By what is DNA made?

A

DNA Polymerase.

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9
Q

What does DNA Polymerase use?

A

Nucleotide triphosphates.

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10
Q

What does DNA Polymerase release?

A

A diphosphate.

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11
Q

What are the key chemical structures in DNA?

A

Bases.
Pentose sugar.
Phosphate.

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12
Q

Where is pentose sugar connected?

A

Bases.

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13
Q

What does pentose sugar form?

A

Nucleoside.

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14
Q

Where is phosphate connected?

A

To nucleoside.

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15
Q

What do the ribose sugar group of nucleic acids have?

A

H group at position 2’ = ‘2 prime’.
OH group at position 3’.
Phosphate group at position 5’.

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16
Q

What does the structure of: H, OH and phosphate give the DNA chain?

A

Specific orientation = 3’ to 5’.

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17
Q

What is the DNA chain?

A

A series of nucleotide monophosphates linked together in a specific orientation with 5’-P end and 3’-OH end.

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18
Q

How are bases always occurred?

A

In particular molar ratios.

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19
Q

How are molar ratios known as?

A

‘Chargaff’s Rules’.

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20
Q

Who established ‘Chargaff’s Rules’ and when?

A

Erwin Chargaff.

In 1947, 1951.

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21
Q

What did Chargaff do?

A
  1. Chemically reduced purified DNA samples to bases.

2. Assessed relative quantities with layer chromatography.

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22
Q

What did Phoebus Levene suggested in 1909?

A

DNA was a series of tetranucleotides.

DNA was a monotonous polymer.

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23
Q

What did Chargaff show?

A

DNA could not be composed of a series of ‘tetranucleotides’, because ratios of 4 bases were different from 1:1:1:1 predicted ratio.

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24
Q

What did Chargaff show about the rations of purines to pyrimidines?

A

=1.

No matter the source of DNA.

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25
Q

How is the ratio of purines to pyrimidines = 1, no matter the DNA source, known?

A

‘Base Pair Rule’.

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26
Q

How should the amount of guanine to cytosine be?

A

Equal.

G = C.

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27
Q

How should the amount of adenine to thymine be?

A

Equal.

A = T.

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28
Q

How could DNA be visualised at single molecule level?

A

By electron microscopy.

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29
Q

What did electron microscopy suggest?

A

DNA was a long, thin and flexible polymer.

30
Q

By what was the structure of DNA finally resolved?

A

By X-ray crystallography.

31
Q

Who used the X-ray crystallography for DNA structure and when?

A

James Watson.
Francis Crick.
Rosland Franklin.
Early 1950s.

32
Q

What can refract X-rays?

A

Solids.

33
Q

How are the X-rays refracted when the solid is composed of a regular array of molecules?

A

In ordered, predictable manner.

34
Q

How is the pattern of X-rays diffracted by solids used?

A

Reconstruct electron densities.

Destruct atomic model for crystallized molecule.

35
Q

By what and who was the DNA structure revealed?

A

X-ray studies.
Rosalind Franklin 1950.
James Watson and Francis Crick 1953.

36
Q

What did Watson and Crick do?

A

Used Rosalind’s data to build physical models.

37
Q

What did Watson and Crick suggest based on Chargaff’s ratios of deoxyribose nucleotides and Franklin’s X-ray data?

A

A structural model of DNA where 2 chains of DNA were bound together.

38
Q

What is DNA?

A

A duplex of 2 strands.

39
Q

Of what is DNA composed?

A

2 oppositely orientated antiparallel strands.

40
Q

Of what are the stairs of ladder made?

A

Paired bases.
A-T : 2H bonds.
C = G : 3H bonds.
= Base pairs.

41
Q

Of what are the sides of ladder made?

A

Alternating ribose sugar units and phosphate groups.

42
Q

What does each end of the duplex have?

A

One 5.

One 3’ end.

43
Q

Into what is duplex twisted?

A

A helix.

44
Q

Where is the ladder twisted?

A

Central core.

45
Q

Why is the ladder twisted at central core?

A

To produce right-handed helix.

46
Q

What is the helix?

A

23.7 A wide.

47
Q

To what does the helix extend?

A

34 A per 10bp of sequence.

48
Q

What does helix make when extends?

A

One complete turn every 10.4-10.5 base pairs.

49
Q

What has been observed in vitro and in cells?

A

DNA different structures.

50
Q

What happens to the pitch and helix direction in different DNA structures?

A

They change.

51
Q

In how many forms does DNA exist?

A

3.

52
Q

Which are the 3 different forms of DNA?

A
  1. A.
  2. B.
  3. Z-DNA.
53
Q

What is the B form of DNA?

A

More relaxed.

More common.

54
Q

Where is Z-DNA form of DNA found?

A

In some cancerous cells.

55
Q

What are the types of the ladder sides?

A

Major groves.

Minor groves.

56
Q

What are the outer edge of the 2 helices from one another?

A

Not evenly spaced.

57
Q

What can the DNA-binding proteins ‘read’?

A

Major grove’s base-pairs.

58
Q

What do phosphodiester bonds link?

A

Phosphate group of one nucleotide to sugar of adjacent nucleotide along double helixes’ side.

59
Q

By which molecule are bases held together?

A

Hydrogen bonds.

60
Q

Which factors stabilize base stacking?

A

Weak hydrophobic forces.

61
Q

Into what is DNA packed?

A

Chromosomes.

62
Q

What are the characteristics of DNA?

A

Too long.

Fragile.

63
Q

Where is DNA ‘stuffed’ ?

A

In cells.

In nuclei.

64
Q

Around what is DNA wrapped?

A

Specialised proteins.

65
Q

Why are DNA-protein loops lopped together?

A

To form chromosomes.

66
Q

When can DNA duplexes join?

A

During chromosomal repair.

67
Q

What do DNA duplexes produce?

A

Halliday Junctions = ‘Chiasma’ in Prophase 1.

68
Q

Into what do ‘Chiasma’ need to be resolved back?

A

Into 2 sister chromosomes before cell division.

69
Q

What can proteins recognise in general?

A

DNA.

70
Q

How else can proteins recognise DNA?

A

Through specific DNA sequences via major groove.

71
Q

What does major groove stabilise?

A

DNA-protein complexes.

72
Q

What do major groove allow when stabilising DNA-protein complexes?

A 
Interactions.
DNA replication.
Repair.
Gene expression.
Regulation.

Molecular Biology and Genetics (15 decks)

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