Lecture 11

Question 1

What does helicase do?

Answer 1

Helicase unwinds the two stranded DNA helix, breaking the H bonds between the nucleotide bases.

Question 2

What does DNA polymerase do?

Answer 2

DNA polymerase is the enzyme that replicates the DNA by building a new strand.

Question 3

What does primase do?

Answer 3

Catalyzes the synthesis of short RNA molecules used as primers for DNA polymerases.

Question 4

What does ligase do?

Answer 4

Joins together fragments of the newly synthesised DNA to form one seamless strand.

Question 5

What are challenges faced when unwinding DNA strands?

Answer 5

DNA helicase uses ATP energy to unbind the H bonds between the DNA helix. To prevent them from rebinding single stranded proteins bind the bases. Topoisomerase cleaves and relegates the DNA backbone to relieve the torsional stress.

Question 6

How many origins do prokaryotic and eukaryotic cells have?

Answer 6

Circular prokaryotic chromosomes have one. Linear eukaryotic chromosomes have multiple.

Question 7

What are the challenges faced in synthesising DNA accurately?

Answer 7

DNA polymerase require a primer to check that each nucleotide is correct.

Question 8

What is the challenge of synthesising antiparallel strands?

Answer 8

DNA polymerase can only add nucleotides to the 3’ end of the template strand, so moves in the 5’-3’ direction. The lagging strand is synthesised discontinuously causing okazaki fragments.