Book 1 - Ch 5

Question 1

Base excision repair

Answer 1

Damaged bases removed
DNA Glycosylases - catalyse cleavage of base from backbone
Sugar phosphate removed by nucleases
DNA polymerase adds correct nucleotide
DNA ligand rejoins sugar phosphate backbone

Question 2

Nucleotide excision repair

Answer 2

Kink caused by dimer forming (eg as result of UV-B)
Kink recognised by repair proteins
Dna strand cleaved each side, DNA on either side unwound and separated by DNA helicase. Gap filled by synthesis of new DNA using intact strand. Gap filled by DNA ligand.

Question 3

Repair of double stranded breaks

Answer 3

Non homologous end joining - protein complex trims damaged ends and ligature them to together
Homologous - damaged DNA pairs with undamaged homologous dna - acts as template to repair both strands accurately

Question 4

What sequence of bases is start codon

Answer 4

AUG

Question 5

Sequence of bases for stop codon

Answer 5

UAA, UAG, UGA

Question 6

Transitions

Answer 6

Substitute of 1 pyridime ( C or T) or of purine ( A or G) by the other

Question 7

Transversions

Answer 7

Replacement of pyridime (c or g) by purine (a or t) or other way round