semi conservative replication

Question 1

stage 2

Answer 1

the exposed strands (templates) attach to short strands of RNA called primers using an enzyme called primase

Question 2

stage 1

Answer 2

• DNA helicase unzips double strand by hydrolysing the hydrogen bonds between nitrogenous base pairs
• the strands are exposed
• the unwound region = replication fork

Question 3

stage 3

Answer 3

DNA polymerase reads the parent strand and aligns free nucleotides with the exposed bases, forming hydrogen bonds

Question 4

stage 4

Answer 4

the enzyme ligase causes a condensation reaction which joins the strands and catalyses the formation of phosphodiester bonds which produces a sugar phosphate backbone

Question 5

describe how DNA polymerase works

Answer 5

• only 5’ to 3’
• leading strand is continuous
• lagging strand is discontinuous as it detaches and reattaches in a backward direction

Question 6

why is DNA replicated before cell division?

Answer 6

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

Question 7

what is a mutation?

Answer 7

random, spontaneous change in the base sequence due to incorrect matching

Question 8

summarise what is meant by semi conservative replication

Answer 8

when a cell prepares for division, the double strand separates and each strand acts as a template for a new double strand to form

Question 9

what is the product of semi conservative replication?

Answer 9

2 new DNA molecules which consist of one old strand and one new strand

Question 10

describe the role of DNA helicase

Answer 10

separates the double strand by travelling along the backbone and catalysing the hydrolysis of hydrogen bonds

Question 11

describe the role of DNA polymerase

Answer 11

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

Question 12

what is the function of DNA?

Answer 12

controls the sequence of amino acids in proteins and passes genetic information between cells

Question 13

what are the 4 adaptations of DNA

Answer 13

• 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 14

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 14

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 15

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

Answer 15

• control concentrations
• control volumes
• control speed