semi-conservative replication

Question 1

the …. strands (templates) attach to short strands of RNA called …. using an enzyme called ….

Answer 1

exposed
primers
primase

Question 2

DNA …. unzips double strand by ….. the hydrogen bonds between …. ….. …..- the strands are ….

Answer 2

helicase
hydrolysing
nitrogenous base pairs
exposed

Question 3

DNA …. reads the parent strand and aligns …. …… with the ….. ….., forming hydrogen bonds

Answer 3

polymerase
free nucleotides
exposed bases

Question 4

the enzyme ….. causes a ….. reaction which joins the strands and catalyses the formation of …… bonds which produces a ….. ….. ….

Answer 4

ligase
condensation
hydrogen
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 it is split equally and produces genetically identical daughter DNA

Question 7

what is a mutation

Answer 7

random, spontaneous change in 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

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 13

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

Question 14

what precautions should be taken to ensure centrifugation produces valid results?

Answer 14

control concentrations
control volumes
control speed