FoM:L1 - DNA and replication Flashcards
1
Q
What does a DNA nucleotide consist of?
A
- sugar: deoxyribose
- base: purine (A, G) or pyrimidines (C, T, U in RNA)
- phosphate
2
Q
How are nucleotides join together?
A
3’ - 5’ phosphodiester bond
3
Q
What are complementary base pairs?
A
- A:T and C:G
- Purine: Pyrimidine
- Hydrogen bonds
4
Q
What is the structure of DNA?
A
- Anti-parallel, double helix
- one strand is 3’ - 5’ , the other is 5’ - 3’
5
Q
How is DNA replicated?
A
- semi-conservative
- parental strands act as templates for synthesis of daughter strand
6
Q
What are replication forks?
A
- where DNA is replicating
- unwound DNA
7
Q
How is DNA unwound?
A
- Helicase
- using ATP
- 5’ - 3’
8
Q
Why is DNA replication semi discontinuous?
A
- no 3’ to 5’ DNA polymerase ONLY 5’ to 3’
- one strand leads, synthesised continuously
- lagging strand, synthesised in Okazaki fragments
9
Q
What is a 3’ to 5’ exonuclease?
A
- ‘proof reads’
- moves backwards
- removes primers
10
Q
What is the role of DNA primase?
A
- synthesises a short RNA primer than DNA polymerase extends
- primers erased by polymerase, fragments joined by ligase
11
Q
What is a clinical application of DNA replication?
A
- chemotherapy
- inhibit DNA replication
- e.g. base analogues 6-mercaptopurine and 5-fluorouracil
12
Q
How is DNA packed into cells?
A
- 2 metres DNA
- stored in chromosomes; made of DNA and proteins called chromatin
13
Q
What is a nucleosome?
A
- 8 histone proteins, 200bp
- DNA wound around histone core, containing 2 of each core histone protein
14
Q
What are chromatin fibres?
A
nucleosomes packed together
15
Q
How many chromosomes do humans have?
A
- 46 - 23 pairs
- 22 autosomes
- 2 sex chromosomes
