DNA and RNA

Question 1

What animal did Griffiths experiment involve and what was the bacterium? (3)

Answer 1

The animal was mice
2 strains of serotype:
Serotype 2 (R) - non pathogenic
Serotype 3 (S) - pathogenic

Question 2

What did Griffith find when he changed conditions of the bacteria? (3)

Answer 2

Heat-killed S type 3 - survived (bacteria dead)
Heat killed S type 3 and normal R type 2 - mouse died

Some property of the dead, S 3 can transform the live R 2 bacteria (DNA released, R converted to S)

Question 3

What did Avery discover from Griffiths experiment?

Answer 3

The transforming principle was DNA

Question 4

Describe the Avery, MacLeod and McCarty experiment: (5)

Answer 4

Used 75L of heat-killed S3 cells
Removed lipids - extract still active
Removed protein - extract still active
Removed polysaccharide - extract still active
Only DNA remaining - extract still active

Question 5

What did the Hershey-Chase experiment demonstrate?

Answer 5

It demonstrated that the genetic material is DNA

Question 6

Describe the stages of the Hershey-Chase experiment: (5)

Answer 6

35S Coat proteins and 32P DNA applied to separate pellets

Blended separately (phage ghosts appear)

Centrifugation

35S remained in the supernatant
32P DNA was mainly in the pellet

Question 7

What is the evidence for DNA structure? (3)

Answer 7

1. Nucleotide structure known
2. X-ray diffraction - helical structure
3. Chargaff’s Law’s - purines (A G) Pyrimidines (T C)

Question 8

What are Chargaff’s Law’s? (2)

Answer 8

1. Total pyrimidines (T,C,[U]) = total purines (A,G)

2. T=A and C=G

Question 9

How many H bonds do A and T have and how many do C and G have?

Answer 9

A=T - 2

C≡G - 3

Question 10

What are the 3 main components of a nucleic acid?

Answer 10

Phosphate
Pentose sugar
Purine or pyrimidine base

Question 11

What is the difference between ribose and deoxyribose?

Answer 11

On the deoxyribose there is no hydroxyl on the 2 carbon

Question 12

What is a nucleoside?

Answer 12

Sugar + base

Question 13

What is a nucleotide?

Answer 13

Sugar + base + phosphate

Question 14

What are the key properties of DNA? (2)

Answer 14

Double alpha helix structure

2 anti-parallel strands held together by H bonds between base pairs

Question 15

What type of handed helix is DNA?

Answer 15

Right handed helix

Question 16

What are the 3 forms of DNA?

Answer 16

A
B
Z

Question 17

What are the key properties of A DNA? (4)

Answer 17

Right handed
11 base pairs in a turn
More compact than B - smaller distance between bases
Large helix diameter

Question 18

What are the key properties of B DNA? (4)

Answer 18

Common DNA found in cells
Right handed
10 base pairs in a turn
Large major groove

Question 19

What are the key properties of Z DNA? (5)

Answer 19

Found in vitro, just GCGCGCGC
Left handed 
Narrow diameter
Stretched
12 base pairs in a turn

Question 20

What happens if you apply heat to DNA and then cool it again?

Answer 20

It denatures and then renatures

Question 21

What are the 3 RNAs?

Answer 21

mRNA - messenger
rRNA - ribosomal
tRNA - transfer

Question 22

What is different about the structure of RNA to DNA (3)

Answer 22

Contains uracil instead of thymine
Contains ribose instead of deoxyribose
Single stranded - single polynucleotide chain

Question 23

What is the structure of RNA?

Answer 23

t shape, clover leaf

Question 24

What does the Hershey-Chase experiment show?

Answer 24

When bacteriophages infect bacteria, their DNA enters the host bacterial cell, but most of their protein does not.