DNA structure

Question 1

What is the name of the backbone?

Answer 1

Phosphodiester

Question 2

Name the bond that forms between 2 bases

Answer 2

Glyosidic bond

Question 3

Describe the structure of the sugar

Answer 3

Primary Alcohol on 5’

Secondary on 3’

Question 4

What is a nucleoside?

Answer 4

sugar + base

Question 5

Name the 4 nucleosides

Answer 5

Adenosine
Thymidine
Guanosine
Cytidine

Question 6

Who created the double helix model?

Answer 6

James Watson and Crick

Question 7

What did Rosalind Franklin discover?

Answer 7

Obtained X-ray Diffraction patterns on DNA fibres

Question 8

Name Chargaff’s rules?

Answer 8

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

Question 9

What did Watson and Crick discover about DNA bases?

Answer 9

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

Question 10

What is nucleotide?

Answer 10

Nucleoside and phosphate

Question 11

Where are the phosphates on DNA helix?

Answer 11

on the outside

Question 12

The DNA molecule has what charge?

Answer 12

Highly negative

Question 13

Describe what is meant by antiparallel?

Answer 13

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

Named Sense/coding strand and template strand

Question 14

Is the DNA helix left or right handed?

Answer 14

Right Handed

Question 15

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

Answer 15

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

Question 16

What is the most stable conformation of DNA ?

Answer 16

B-DNA

Question 17

What grooves does B-DNA have ?

Answer 17

2 grooves of unequal size

Question 18

What are the 3 forms of DNA?

Answer 18

B-DNA Z-DNA A-DNA

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

Describe DNA melting

Answer 21

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

Question 22

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

Answer 22

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

Question 23

Why is strand separation beneficial for DNA?

What causes it?

Answer 23

Allows for DNA replication or transcription

Helicases carry this out

Question 24

What is the hyperchromic effect?

Answer 24

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

Question 25

What is the difference in the maximal absorbance of single and double stranded DNA?

Answer 25

Single stranded have higher absorbency than double stranded

Question 26

When is the midpoint of the translation in DNA melting?

Answer 26

Tm(‘C) 50% double 50% single stranded

Question 27

What is the relationship between absorbance and denaturing in DNA melting?

Answer 27

Absorbance increases as it denatures

Question 28

Which melt at a higher temperature GC or AT and why?

Answer 28

GC melt at higher temperature due to 3 H bonds

Question 29

Which melts at a higher temperature longer or shorter DNA fragments?

Answer 29

Longer

Question 30

Which salt concentration melts at a higher temperature and why?

Answer 30

Higher salt concentration due to positive ions neutralising repulsive negative phosphate groups

Question 31

Which melts at a higher temperature low or high ionic strength?

Answer 31

Low ionic strength= greater melting