1.5.8 The Process of Semi-Conservative Replication

Question 1

DNA replication occurs in preparation for

Answer 1

mitosis

Question 2

DNA replication occurs in preparation for mitosis, when

Answer 2

a parent cell divides to produce two genetically identical daughter cells – as each daughter cell contains the same number of chromosomes as the parent cell, the number of DNA molecules in the parent cell must be doubled before mitosis takes place

Question 3

DNA replication occurs during the what phase of the cell cycle

Answer 3

S phase (which occurs during interphase, when a cell is not dividing)

Question 4

The enzyme

Answer 4

helicase

Question 5

The enzyme helicase

Answer 5

unwinds the DNA double helix

Question 6

The enzyme helicase unwinds the DNA double helix by

Answer 6

breaking the hydrogen bonds

Question 7

The enzyme helicase unwinds the DNA double helix by breaking the hydrogen bonds between

Answer 7

the base pairs on the two antiparallel polynucleotide DNA strands

Question 8

The enzyme helicase unwinds the DNA double helix by breaking the hydrogen bonds between the base pairs on the two antiparallel polynucleotide DNA strands to form

Answer 8

two single polynucleotide DNA strands

Question 9

Each of these single polynucleotide DNA strands acts as

Answer 9

a template

Question 10

Each of these single polynucleotide DNA strands acts as a template for

Answer 10

the formation of a new strand

Question 11

Each of these single polynucleotide DNA strands acts as a template for the formation of a new strand made from

Answer 11

free nucleotides

Question 12

ach of these single polynucleotide DNA strands acts as a template for the formation of a new strand made from free nucleotides that are attracted to

Answer 12

the exposed DNA bases

Question 13

Each of these single polynucleotide DNA strands acts as a template for the formation of a new strand made from free nucleotides that are attracted to the exposed DNA bases by

Answer 13

base pairing

Question 14

The new nucleotides are then joined together by

Answer 14

DNA polymerase

Question 15

The new nucleotides are then joined together by DNA polymerase which

Answer 15

catalyses condensation reactions to form a new strand

Question 16

The original strand and the new strand joined together through

Answer 16

hydrogen bonding between base pairs to form the new DNA molecule

Question 17

This method of replicating DNA is known as semi-conservative replication because

Answer 17

half of the original DNA molecule is kept (conserved) in each of the two new DNA molecules

Question 18

Semi-conservative replication of DNA

Answer 18

Question 19

In the nucleus, there are free

Answer 19

nucleotides

Question 20

In the nucleus, there are free nucleotides which contain

Answer 20

three phosphate groups

Question 21

Free nucleotides, which contain three phosphate groups, are known as

Answer 21

nucleoside triphosphates or ‘activated nucleotides’

Question 22

The extra phosphates activate

Answer 22

the nucleotides

Question 23

The extra phosphates activate the nucleotides, enabling them to

Answer 23

take part in DNA replication

Question 24

The bases of the free nucleoside triphosphates align with their

Answer 24

complementary bases

Question 25

The bases of the free nucleoside triphosphates align with their complementary bases on

Answer 25

each of the template DNA strands

Question 26

Which enzyme synthesises new DNA strands from the two template strands

Answer 26

DNA polymerase

Question 27

The enzyme DNA polymerase synthesises

Answer 27

new DNA strands from the two template strands

Question 28

The enzyme DNA polymerase synthesises new DNA strands from the two template strands, it does this by

Answer 28

catalysing condensation reactions between the deoxyribose sugar and phosphate groups of adjacent nucleotides within the new strands

Question 29

The enzyme DNA polymerase synthesises new DNA strands from the two template strands, it does this by catalysing condensation reactions between the deoxyribose sugar and phosphate groups of adjacent nucleotides within the new strands, creating

Answer 29

the sugar-phosphate backbone of the new DNA strands

Question 30

DNA polymerase cleaves (breaks off) the two extra phosphates and uses the energy released to create

Answer 30

the phosphodiester bonds (between adjacent nucleotides)

Question 31

Hydrogen bonds then form between

Answer 31

the complementary base pairs of the template and new DNA strands

Question 32

Nucleotides are bonded together by DNA polymerase to create the new complementary DNA strands

Answer 32

Question 33

DNA polymerase can only build the new strand in one direction

Answer 33

5’ to 3’ direction

Question 34

As DNA is ‘unzipped’ from the 3’ towards the 5’ end, DNA polymerase will

Answer 34

attach to the 3’ end of the original strand

Question 35

As DNA is ‘unzipped’ from the 3’ towards the 5’ end, DNA polymerase will attach to the 3’ end of the original strand and

Answer 35

move towards the replication fork (the point at which the DNA molecule is splitting into two template strands)

Question 36

This means the DNA polymerase enzyme can synthesise the leading strand

Answer 36

continuously

Question 37

This template strand that the DNA polymerase attaches to is known as

Answer 37

the leading strand

Question 38

The other template strand created during DNA replication is known as

Answer 38

the lagging strand

Question 39

On the lagging strand, DNA polymerase moves away from

Answer 39

replication fork (from the 5’ end to the 3’ end)

Question 40

This means the DNA polymerase enzyme can only synthesise the lagging DNA strand in

Answer 40

short segments (called Okazaki fragments)

Question 41

A second enzyme known as

Answer 41

DNA ligase

Question 42

A second enzyme known as DNA ligase is needed to

Answer 42

join these lagging strand segments together to form a continuous complementary DNA strand

Question 43

DNA ligase does this by

Answer 43

catalysing the formation of phosphodiester bonds

Question 44

DNA ligase does this by catalysing the formation of phosphodiester bonds between the segments to create

Answer 44

a continuous sugar-phosphate backbone

Question 45

The synthesis of the complementary strands occurs slightly differently on the leading and lagging template strands of the original DNA molecule that is being replicated

Answer 45