DNA Replication and repair

Question 1

Which bases are the pyrimidines?

Answer 1

Cytosine and thymine

Question 2

What is a nucleoside?

Answer 2

Base and sugar

Question 3

How are strands separated before replication?

Answer 3

Initiator proteins recognise replication origins and open up helix locally

Question 4

How is DNA synthesised?

Answer 4

Bases added as dNTPs (deoxyribonucleotide triphosphates), energy required for synthesis from hydrolysis of high energy dNTP bond

Question 5

Describe semidiscontinous replication

Answer 5

Lagging strand synthesised discontinuously as DNA Ligase joins short okazaki fragments

Question 6

Why are RNA primers needed?

Answer 6

DNA Polymerase cannot initiate new strands so extends RNA chain, later removed by nuclease

Question 7

How are errors avoided?

Answer 7

DNA Polymerase proofreads own work, 1 in 10^7 error

Question 8

Describe DNA mismatch repair

Answer 8

DNA mismatch repair proteins bind, remove newly synthesised DNA strand, gap repaired by DNA Polymerase and Ligase

Question 9

How is DNA damaged continuously?

Answer 9

Spontaneous intracellular chemical reactions (depurination/ deamination), UV exposure forms thymine dimers

Question 10

What is xeroderma pigmentosum?

Answer 10

Genetic defect, cant repair thymine dimers, skin lesions and cancer

Question 11

What is synthetic lethality?

Answer 11

Treatment with drugs that inhibit second alternative repair pathway so tumour cells cannot repair DNA damage due to mutated BRCA gene leading to apoptosis