L2 - DNA replication , damage , repair pathways

Question 1

Primer ability:

Answer 1

Can bring the first two nucleotides together ( usually in DNA replication )

Question 2

DNA polymerase features

Answer 2

• replicate DNA
• Synthesised 5’–3’
• needs a primer

Question 3

DNA Replication in prokaryote process

Answer 3

Origin of replication
Bidirectional
Theta structure
2 daughter molecules

Question 4

5’— 3’ explanation

Answer 4

5’ refers to no. Of carbons on sugar phosphate back bone

5’ has PHOSPHATE group attached
3’ connected to hydroxyl group – 0H

5’ – 3’ : nucleiotides added to the 3’

Question 5

Exonuclease activity :

Answer 5

Proof reading activity that DNA polymerase has but RNA polymerase does not

Question 6

Problems with DNA polymerase replicating DNA

Answer 6

1 5’ - 3’ problèm

• DNA can only be synthesised in 5’ – 3’ direction
• but DNA has 2 strands & are anti parallel- thus one is 5-3 & other is 3-5
• 5-3 is fine &; DNA is replicated immediately on this strand
• BUT : other one must be split into OKAZAKI FRAGMENTS - so DNA can be made in correct direction

2. Primer needed
   DNA polymerase can NOT bring first two nucleotides together - need RNA primer
3. RNA PRIMER PROBLEM
   - Does not have PROOf READING activity - prone to make mistakes
   - This primer contains ribonuceotides which are bad !!!
   - Also less stable than DNA

Solution

• DNA polymerase 1 comes back
• Replaces RNA primer which DNA primers

Question 7

NDP :

Answer 7

Nucleotide had 2 phosphates

Called nucleoside diphosphate

Question 8

Types of mutation

Answer 8

Deletion
Insertion
???? More

Question 9

How DNA can be damaged

Answer 9

• UV LIGHT
• cellular metabloslim
• Replication errors
• Ionising radiation or chemical exposure

Question 10

DNA POLYMERASE 1

How it works

Answer 10

NTP- n refers to any of the 4 possible bases

• removes NTP’s using 5’ - 3’ exonuclese activity
• replaces Them with dNTP (nucleotide with 3 phosphates) using 5-3 SYNTHETIC activity
• proof reads using 3-5 exonuclease activity

Think the no D then D means rna to DNA primers

Question 11

Topoisomerase

Answer 11

Enzyme that takes part in the over or under winding of DNA

They bind to DNA to cut phosphate back bone

This is to allow DNA to untangle etc

Topoisomerase then puts back on the phosphate back bone

human topoisomerase is chemotherapy

Why????? Chemo relation to DNA ???

Question 12

Repair pathways work to

Answer 12

• Remove offending. Or wrong base
• replace bases
• fill the gap

Question 13

Repair pathways ex.

Answer 13

Base excision repair : removes damaged bases that could cause mutations if not removed

Nucleotide excision damage :
Removes DNA damage caused by UV light

Mismatch repair
Recognises and repairs mutations like deletion & insertion ie bases are MISMATCHED

Direct repair of DNA
- occurs when only one of the strands is damaged & ; thus the other strand can be used to correct the damaged one

Double strand break repair Both strands are damaged
Repair system is complicated

Question 14

Defects in repair mechanisms

Answer 14

• increased cancer risk

- neurodegeneration

Question 15

DNA REPLICATION PROCESS

Answer 15

DNA helicase breaks the HB between the tangled strand of DNA thus separating them into 2 separate strands

complementary base paring
HB form due to condensation reaction catalysed by DNA polymerase

2 DNA molecules = #replicated