The Watson and Crick model of DNA

Question 1

Of what does DNA consist?

Answer 1

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

Question 2

How many types of bases exist?

Answer 2

2.

Question 3

Which are the 2 types of bases?

Answer 3

Purines (A, G).

Pyrimidines (C, T and U).

Question 4

What is the characteristic of Purine bases?

Answer 4

Double-ring structure.

Question 5

What is the characteristic of Pyrimidine bases?

Answer 5

Single-ring structure.

Question 6

Of what are bases a part?

Answer 6

Larger subunits = nucleosides and nucleotides.

Question 7

What is the nucleotide monophosphate?

Answer 7

Building-block of DNA polymer.

Question 8

By what is DNA made?

Answer 8

DNA Polymerase.

Question 9

What does DNA Polymerase use?

Answer 9

Nucleotide triphosphates.

Question 10

What does DNA Polymerase release?

Answer 10

A diphosphate.

Question 11

What are the key chemical structures in DNA?

Answer 11

Bases.
Pentose sugar.
Phosphate.

Question 12

Where is pentose sugar connected?

Answer 12

Bases.

Question 13

What does pentose sugar form?

Answer 13

Nucleoside.

Question 14

Where is phosphate connected?

Answer 14

To nucleoside.

Question 15

What do the ribose sugar group of nucleic acids have?

Answer 15

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

Question 16

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

Answer 16

Specific orientation = 3’ to 5’.

Question 17

What is the DNA chain?

Answer 17

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

Question 18

How are bases always occurred?

Answer 18

In particular molar ratios.

Question 19

How are molar ratios known as?

Answer 19

‘Chargaff’s Rules’.

Question 20

Who established ‘Chargaff’s Rules’ and when?

Answer 20

Erwin Chargaff.

In 1947, 1951.

Question 21

What did Chargaff do?

Answer 21

1. Chemically reduced purified DNA samples to bases.

2. Assessed relative quantities with layer chromatography.

Question 22

What did Phoebus Levene suggested in 1909?

Answer 22

DNA was a series of tetranucleotides.

DNA was a monotonous polymer.

Question 23

What did Chargaff show?

Answer 23

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

Question 24

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

Answer 24

=1.

No matter the source of DNA.

Question 25

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

Answer 25

'Base Pair Rule'.

Question 26

How should the amount of guanine to cytosine be?

Answer 26

Equal. | G = C.

Question 27

How should the amount of adenine to thymine be?

Answer 27

Equal. | A = T.

Question 28

How could DNA be visualised at single molecule level?

Answer 28

By electron microscopy.

Question 29

What did electron microscopy suggest?

Answer 29

DNA was a long, thin and flexible polymer.

Question 30

By what was the structure of DNA finally resolved?

Answer 30

By X-ray crystallography.

Question 31

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

Answer 31

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

Question 32

What can refract X-rays?

Answer 32

Solids.

Question 33

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

Answer 33

In ordered, predictable manner.

Question 34

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

Answer 34

Reconstruct electron densities. | Destruct atomic model for crystallized molecule.

Question 35

By what and who was the DNA structure revealed?

Answer 35

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

Question 36

What did Watson and Crick do?

Answer 36

Used Rosalind's data to build physical models.

Question 37

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

Answer 37

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

Question 38

What is DNA?

Answer 38

A duplex of 2 strands.

Question 39

Of what is DNA composed?

Answer 39

2 oppositely orientated antiparallel strands.

Question 40

Of what are the stairs of ladder made?

Answer 40

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

Question 41

Of what are the sides of ladder made?

Answer 41

Alternating ribose sugar units and phosphate groups.

Question 42

What does each end of the duplex have?

Answer 42

One 5. | One 3' end.

Question 43

Into what is duplex twisted?

Answer 43

A helix.

Question 44

Where is the ladder twisted?

Answer 44

Central core.

Question 45

Why is the ladder twisted at central core?

Answer 45

To produce right-handed helix.

Question 46

What is the helix?

Answer 46

23.7 A wide.

Question 47

To what does the helix extend?

Answer 47

34 A per 10bp of sequence.

Question 48

What does helix make when extends?

Answer 48

One complete turn every 10.4-10.5 base pairs.

Question 49

What has been observed in vitro and in cells?

Answer 49

DNA different structures.

Question 50

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

Answer 50

They change.

Question 51

In how many forms does DNA exist?

Answer 51

3.

Question 52

Which are the 3 different forms of DNA?

Answer 52

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

Question 53

What is the B form of DNA?

Answer 53

More relaxed. | More common.

Question 54

Where is Z-DNA form of DNA found?

Answer 54

In some cancerous cells.

Question 55

What are the types of the ladder sides?

Answer 55

Major groves. | Minor groves.

Question 56

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

Answer 56

Not evenly spaced.

Question 57

What can the DNA-binding proteins 'read'?

Answer 57

Major grove's base-pairs.

Question 58

What do phosphodiester bonds link?

Answer 58

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

Question 59

By which molecule are bases held together?

Answer 59

Hydrogen bonds.

Question 60

Which factors stabilize base stacking?

Answer 60

Weak hydrophobic forces.

Question 61

Into what is DNA packed?

Answer 61

Chromosomes.

Question 62

What are the characteristics of DNA?

Answer 62

Too long. | Fragile.

Question 63

Where is DNA 'stuffed' ?

Answer 63

In cells. | In nuclei.

Question 64

Around what is DNA wrapped?

Answer 64

Specialised proteins.

Question 65

Why are DNA-protein loops lopped together?

Answer 65

To form chromosomes.

Question 66

When can DNA duplexes join?

Answer 66

During chromosomal repair.

Question 67

What do DNA duplexes produce?

Answer 67

Halliday Junctions = 'Chiasma' in Prophase 1.

Question 68

Into what do 'Chiasma' need to be resolved back?

Answer 68

Into 2 sister chromosomes before cell division.

Question 69

What can proteins recognise in general?

Answer 69

DNA.

Question 70

How else can proteins recognise DNA?

Answer 70

Through specific DNA sequences via major groove.

Question 71

What does major groove stabilise?

Answer 71

DNA-protein complexes.

Question 72

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

Answer 72

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