DNA REPLICATION

Question 1

What are the 2 main stages of cell division

Answer 1

1) nuclear division

2) cytokinesis

Question 2

What is nuclear division

Answer 2

process in which the nuclear divides

Question 3

How many types of nuclear division are there and what are they

Answer 3

2

1) meiosis
2) mitosis

Question 4

What is cytokinesis

Answer 4

follows nuclear division and in the process by which the whole cell divides

Question 5

What must happen to the DNA before a cell divides and why

Answer 5

it is replicated (copied), so that the daughter cells have the genetic info to produce the enzymes and other proteins they need

Question 6

What is the universally accepted method of DNA replication

Answer 6

semi-conservative replication

Question 7

What are the 4 requirements of DNA replication

Answer 7

1) four types of nucleotide with their bases must be present
2) both strands of DNA molecule act as a template for the attachment of these nucleotides
3) the enzyme DNA polymerase
4) source of chemical energy (to drive the process)

Question 8

How many stages of semi-conservative replication are there

Answer 8

5

Question 9

What are the stages of semi-conservative replication

Answer 9

1) enzyme DNA helicase breaks the hydrogen bonds between the complementary bases of the 2 strands
2) the strands unwind and seperate
3) each separate strand acts as a template and free nucleotides that have been activated bind to the complementary base on the template strand by specific base pairing
4) the now attached free nucleotides are joined together by DNA polymerase with phospodiester bonds whilst the other nucleotides continue to attract complementary nucleotides
5) the nucleotides are joined by DNA polymerase to form a polynucleotide chain

Question 10

What does semi-conservative replication result in

Answer 10

each strand containing one strand of the original DNA molecule and one new strand

Question 11

Which direction does DNA polymerase move in

Answer 11

opposite / antiparallel

Question 12

What end does DNA polymerase bind to

Answer 12

the 3’ end

Question 13

Why is DNA polymerase complementary to the 3’ end of DNA strands

Answer 13

the active site of DNA polymerase is only complementary to the 3’ end

Question 14

What does DNA poymerase being complementary to the 3’ end mean

Answer 14

that it only attaches nucleotides to the new strand at the 3’ end

Question 15

Who found the evidence for semi-conservative replication

Answer 15

Meselson and Stahl

Question 16

What were the 2 original hypotheses of DNA replication

Answer 16

1) conservative

2) semi-conservative

Question 17

What is conservative replication

Answer 17

suggested original DNA moecule remained intact and a seperate DNA daughter molecule was built from new molecules of deoxyribose, phosphate and organic bases

Question 18

What would conservative replication result in

Answer 18

one molecule of original DNA strands, one molecule of new DNA strands

Question 19

What would semi-conservative replication result in

Answer 19

Each molecule contains one strand of original DNA and one strand of new DNA

Question 20

What 3 things did Meselson and Stahl base their work on

Answer 20

1) all bases in DNA contain nitrogen
2) nitrogen has 2 forms
3) bacteria will incorporate nitrogen from their growing medium into any DNA they make

Question 21

What experiment did Meselson and Stahl carry out to test DNA replication

Answer 21

1) grew 2 samples of bacteria - one in light (N14) and one in heavy (N15) nitrogen , as they grew they would take up nitrogen into DNA
2) took sample from each batch of bacteria and suspended in solution, then was spun in a centrifuge - light DNA = settled at top (lighter), heavy DNA = settled at bottom (heavier)
3) took bacteria grown in heavy bacteria out, grew in broth containing only light nitrogen and left for one round of DNA replication
4) sample taken from each and spun in centrifuge - DNA settled in middle, showing it contained mixture of heavy & light = semi-conservative