Unit 1: DNA & The Genome - Key Area 2: DNA replication

Question 1

enzyme that adds free complementary DNA nucleotides during replication of DNA

Answer 1

DNA polymerase

Question 2

technique used to separate macromolecules such as DNA fragments of different sizes

Answer 2

gel electrophoresis

Question 3

enzyme from hot-spring bacteria used in PCR

Answer 3

heat tolerant DNA polymerase

Question 4

DNA strand which is replicated in fragments

Answer 4

lagging strand

Question 5

DNA strand which is replicated continuously

Answer 5

leading strand

Question 6

enzyme that joins fragments of DNA to make the lagging strand

Answer 6

ligase

Question 7

method of amplifying sequences of DNA in vitro

Answer 7

Polymerase Chain Reaction (PCR)

Question 8

short complementary strand of DNA

Answer 8

Primer

Question 9

formation of identical copies of DNA molecules

Answer 9

replication

Question 10

DNA strand on which a complementary copy is made

Answer 10

template strand

Question 11

define DNA replication

Answer 11

involves the production of two genetically identical strands of DNA

Question 12

when does DNA replication occur?

Answer 12

prior to cell division (mitosis and meiosis)

Question 13

what is DNA replication described as

Answer 13

semi-conservation as each daughter DNA molecule ends up with one of the original strands of the parental DNA and one newly synthesized strands.

Question 14

what is the function of ‘helicase’ in DNA replication

Answer 14

causes DNA to unwind

Question 15

what is the function of ‘ligase’ in DNA replication?

Answer 15

joins fragments of DNA on the lagging strand

Question 16

what is the function of ‘DNA polymerase’ in DNA replication?

Answer 16

adds free nucleotides using complementary base pairing to the deoxyribose 3’ end of the new DNA strand that is forming

Question 17

what are the requirements of DNA replication?

Answer 17

> original DNA template 
> free DNA nucleotides
> DNA polymerase 
> primers
> ligase

Question 18

what is the function of a ‘primer’ in DNA replication?

Answer 18

binds to the 3’ end of the template DNA strand allowing DNA polymerase to add free nucleotides

Question 19

what is the first step of DNA replication?

Answer 19

the double helix structure of DNA is unwound and hydrogen bonds between bases are broken to form two template strands

Question 20

what is the second step of DNA replication?

Answer 20

two replication forks form and open the double-strand in opposite directions, exposing the bases

Question 21

what is the third step of DNA replication?

Answer 21

A primer binds to each strand of DNA

Question 22

what is the fourth step of DNA replication?

Answer 22

DNA polymerase adds DNA nucleotides using complementary base pairing to the deoxyribose 3’ end of the new DNA strand which is forming

Question 23

what is the fifth step of DNA replication?

Answer 23

DNA polymerase can only add nucleotides in one direction, resulting in the leading strand being replicated continuously and the lagging strand being replicated in fragments

Question 24

what is the sixth step of DNA replication?

Answer 24

Fragments of DNA are joint together by ligase

Question 25

what is PCR (polymerase chain reaction) used for?

Answer 25

to amplify a desired DNA sequence

Question 26

what are the requirements of PCR?

Answer 26

``` > nucleotides > primers > heat tolerant polymerase > template DNA > buffer > thermal cycler ```

Question 27

why does PCR use primers?

Answer 27

Polymerase can only add nucleotides to an existing strand of DNA so PCR requires primers

Question 28

why does PCR need two primers per cycle?

Answer 28

Because primers are short strands of nucleotides which are complementary to specific target sequences and there are two ends of the region of DNA to be amplified thus requiring two primers.

Question 29

what is the first step of PCR?

Answer 29

Heating: DNA molecule to be amplified is denatured by heating to between 92-98 degrees celsius, breaking hydrogen bonds between base pairs to separate the two strands

Question 30

what is the second step of PCR?

Answer 30

Annealing: | DNA is cooled to between 50-65 degrees celsius to allow the primers to bind to target sequences

Question 31

what is the third step of PCR?

Answer 31

Extension: | DNA is then heated to between 70-80 degrees celsius for heat-tolerant DNA polymerase to replicate the region of DNA

Question 32

what is the fourth step of PCR?

Answer 32

two strands are formed and this cycle is repeated 30 times

Question 33

how is DNA amplified in PCR?

Answer 33

in vitro (outside of a living organism)

Question 34

what are the uses/ applications of PCR?

Answer 34

> paternity testing > crime scene analysis > diagnosis of genetic disorders