DNA and RNA

Question 1

What are the genereal structure of DNA and RNA

Answer 1

• double helix structure
  contains sugar photsphate backbone with Nitrogen
  contains organic base pairs in centre

Question 2

3 components

Answer 2

Phosphate,
pentose sugar
organic base

Question 3

differences between DNA and RNA

Answer 3

RNA contains Thymine
pentose sugar is always ribose whereas in dNA its Deoxribose

Question 4

What are the base pairs

Answer 4

adenine - thymine (uracil for RNA)
Cytosine - Guanine

Question 5

How many hydrogen bonds are there

Answer 5

2 for A-T
3 for C-G

Question 6

How is DNA stable

Answer 6

• the phosphodiester backbone protects the more chemically reactive bases inside double helix
• C-G has 3 bonds so DNA molecules with more C-G bonds are more stable
• interactive forces between base paris holds the molecule together (base stacking)

Question 7

Structure and function

Answer 7

1. Phosphodiester backbone = protects organic bases reacting with environment
2. Long molecule - stores alot of genetic information
3. double helix - DNA is compact
4. Weak Hydrogen bonds join base pairs: can be seperated more easily for replication from template strands
5. Base sequence = allows information to be stores to dertermone amino acid sequence
6. Base stacking = stable

Question 8

what 4 things are needed for DNA replication?

Answer 8

1. DnA molecule to bbe replicated
2. Free DNA nucleotides
3. DNA helicase enzyme
4. DNA polymerase enzyme

Question 9

Describe how DNA is replicated

Answer 9

-Strands seperate and H bonds break
-DNa helicase involved
- Both strands act as templates
- Free nucelotides attatched
5. H bonds Reform
6. complimentary pairing
7. DNA polymerase joins nucleotides forming phosphodiester bonds
8. semi-conservative replication = new DNA molecules contain 1 old strand and 1 new strand

Question 10

Describe the Meselson and Stahl experiment

Answer 10

1. Population cultured in a growth medium containing heavy nitrogen only
2. When centriduged only one heavy band is observed
3. Cells transferred to a medium with only light nitrogen
4. After one repliocation the DNA band was intermeditate - twice the thickness
5. After two replications in light nitrogen the intermeduate and light bands were observed
6. this proved DNA replicatuon is semi conservative