dna replication

Question 1

describe how translation leads to the production of a polypeptide.

Answer 1

mRNA associates with a ribosome
Ribosome moves to the start codon
tRNA brings specific amino acid
Anticodon on tRNA complementary to codon on mRNA
Ribosome moves along to next codon (ribosome fits two tRNA’s
amino acids join by peptide bonds

Question 2

Describe and explain how the structure of DNA results in accurate replication

Answer 2

• two strands therefore semi-conservative replication
• base pairing / hydrogen bonds holds strands together
• hydrogen bonds weak / easily broken, allow strands to separate
• bases (sequence) (exposed so) act as template
• A with T, C with G
• DNA one parent and one new strand

Question 3

Describe how DNA is replicated

Answer 3

• H-bonds break
• DNA helicase (involved)
• each strand act(s) as (a) template
• (Free) nucleotides attach
• Complementary bases AT and CG
• DNA polymerase joins nucleotides
• H-bonds reform
• Semi-conservative replication / new DNA molecules contain one old strand and one new strand

Question 4

evidence for semi conservative replication

Answer 4

Meselson and Stahl experiment:

• two samples of bacteria one grown in light nitrogen one in heavy
• sample of DNA taken from both populations and spun in centrifuge heavy DNA separate from light DNA
• bacteria from heavy are put in light nitrogen for one round of replication
• new bacteria should have 1 strand from old heavy nitrogen and 1 light so should settle between light and heavy when spun in centrifuge again