DNA structure Flashcards

1
Q

What is the name of the backbone?

A

Phosphodiester

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2
Q

Name the bond that forms between 2 bases

A

Glyosidic bond

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3
Q

Describe the structure of the sugar

A

Primary Alcohol on 5’

Secondary on 3’

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4
Q

What is a nucleoside?

A

sugar + base

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5
Q

Name the 4 nucleosides

A

Adenosine
Thymidine
Guanosine
Cytidine

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6
Q

Who created the double helix model?

A

James Watson and Crick

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7
Q

What did Rosalind Franklin discover?

A

Obtained X-ray Diffraction patterns on DNA fibres

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8
Q

Name Chargaff’s rules?

A
Number of A=T and C=G
The purines (A+G) = pyrimidines (C+T)
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9
Q

What did Watson and Crick discover about DNA bases?

A
Bases are on the inside and hydrophobic
CG pairings have 3 H bonds
AT pairings have 2 H bonds
But pairs are same size and shape
Separation distance of stacked bases are optimal for Van Der Wal forces
Bases and connected by H bonds
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10
Q

What is nucleotide?

A

Nucleoside and phosphate

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11
Q

Where are the phosphates on DNA helix?

A

on the outside

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12
Q

The DNA molecule has what charge?

A

Highly negative

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13
Q

Describe what is meant by antiparallel?

A

2 strands. One runs 5’ to 3’ the other 3’ to 5’

Named Sense/coding strand and template strand

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14
Q

Is the DNA helix left or right handed?

A

Right Handed

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15
Q

Where is the base pairs in comparison to the helix axis?

A

Base pairs perpendicular to helix axis, the centre of the helix runs through the axis

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16
Q

What is the most stable conformation of DNA ?

17
Q

What grooves does B-DNA have ?

A

2 grooves of unequal size

18
Q

What are the 3 forms of DNA?

A

B-DNA Z-DNA A-DNA

19
Q
A-DNA
Left or right handed?
How is it formed?
What is its difference between this and B-DNA?
How many bases per turn
A

Right Handed
Formed when DNA is dehydrated
Wider, bases tilted of set from axis
11 bases per turn

20
Q

Z-DNA
Left or right handed?
How is it formed?
How many bases per turn

A

Left handed
Formed by some GC containing sequences at high salt concentrations
12 bases pairs per turn

21
Q

Describe DNA melting

A

The process by which double-stranded deoxyribonucleic acid unwinds and separates into single-stranded strands through the breaking of hydrogen bonding between the bases.

22
Q

In the lab how do we seperate DNA strands in solution?

A

heating or addition of acid/alkali agents to alter the pH

23
Q

Why is strand separation beneficial for DNA?

What causes it?

A

Allows for DNA replication or transcription

Helicases carry this out

24
Q

What is the hyperchromic effect?

A

The hyperchromic effect is the striking increase in absorbance of DNA upon denaturation

25
What is the difference in the maximal absorbance of single and double stranded DNA?
Single stranded have higher absorbency than double stranded
26
When is the midpoint of the translation in DNA melting?
Tm('C) 50% double 50% single stranded
27
What is the relationship between absorbance and denaturing in DNA melting?
Absorbance increases as it denatures
28
Which melt at a higher temperature GC or AT and why?
GC melt at higher temperature due to 3 H bonds
29
Which melts at a higher temperature longer or shorter DNA fragments?
Longer
30
Which salt concentration melts at a higher temperature and why?
Higher salt concentration due to positive ions neutralising repulsive negative phosphate groups
31
Which melts at a higher temperature low or high ionic strength?
Low ionic strength= greater melting