semi-conservative replication

Question 1

stage 1

Answer 1

DNA helicase breaks the hydrogen bonds between the complimentary bases of two DNA polymers, which causes the double helix to unwind and the two strands separate

Question 2

stage 2

Answer 2

both strands act as a template for DNA replication

Question 3

stage 3

Answer 3

free-floating activated DNA nucleotides align opposite their complimentary base on the template strand of DNA. Hydrogen bonds form between the base pairs

Question 4

stage 4

Answer 4

DNA polymerase joins adjacent DNA nucleotides together, forming a phosphodiester bond between these nucleotides to create a new polymer chain of DNA

Question 5

define semi-conservative replication

Answer 5

Two new identical DNA molecules are formed each containing one original template strand and one newly synthesised strand of DNA.

Question 6

what is the role of DNA helicase?

Answer 6

travels along DNA backbone, catalysing reactions that break hydrogen bonds between complimentary base pairs, separating two strands of DNA

Question 7

what is the role of DNA polymerase?

Answer 7

catalyses the formation of phosphodiester bonds between free nucleotides and template strands

Question 8

when does DNA replication occur

Answer 8

this occurs during the interphase of mitosis and meiosis

Question 9

why is DNA replicated before cell division?

Answer 9

so that it is split equally and produces genetically identical daughter DNA

Question 10

what are the 4 adaptations of DNA?

Answer 10

• stable: 2 strands, specific base pairs, many H bonds, helix shape, reduces risk of molecular damage
• strands separate: can self replicate
• base pairings: prevents corruption from chemical or physical forces
• large molecule: carry lots of info

Question 11

after replication, the amount of nitrogen went from one band of heavy nitrogen to one band of heavy AND light nitrogen. how does this support the hypothesis of DNA replication? (4 marks)

Answer 11

after replication, the DNA contained both nitrogen isotopes which shows that the DNA replicated contains half new and half original. it contains one heavy strand and one light strand so 2 new DNA molecules have formed between complementary base pairs.

Question 12

what precautions should be taken to ensure centrifugation produces valid results? (3 marks)

Answer 12

• control concentrations
• control volumes
• control speed