DNA Replication (D1.1)

Question 1

Describe semi-conservative DNA replication (5)

Answer 1

hydrogen bonds between bases break through enzyme helicase

DNA splits into 2 strands

enzyme DNA polymerase moves along strands

free floating nucleotides pair with complementary base in strands

2 DNA helixes form

Question 2

Reasons for DNA Replication (2)

Answer 2

cell division - new cells need new DNA for growth + tissue repair

reproduction - gametes require DNA to pass on genetic information

Question 3

Function of PCR in DNA (2)

Answer 3

polymerase chain reaction

amplifies small fragments of DNA (increases quantity of DNA)

Question 4

Uses of PCR in DNA (4)

Answer 4

Covid tests

paternity testing

DNA in crime scenes

clones genes

Question 5

First Step of PCR process (melting/denaturation) (2)

Answer 5

heating to 95 degrees for 30 to 60 seconds

hydrogen bonds between DNA strands broken

Question 6

2nd Step of PCR process (annealing) (2)

Answer 6

sample cools to 60 degrees

short primer sequences bond to complementary sequences of DNA

Question 7

3rd Step of PCR process (extention phase) (2)

Answer 7

Taq polymerase replicates DNA using primers as starting point

once DNA is replicated, DNA is heated to separate + cycle repeats

Question 8

Conditions of PCR process (2)

Answer 8

Taq polymerase - heat-stable version of DNA polymerase

primers - short single strand of DNA to allow replication to occur from desired point

Question 9

Purpose of gel electrophoresis (2)

Answer 9

identify key features of DNA

through separating parts of DNA

Question 10

Process of gel electrophoresis (6)

Answer 10

electric field created by voltage applied across electrodes

charged molecules move through gel

DNA placed in wells in one side of gel

DNA moves towards positive anode due to negative electric charge in phosphates

smaller pieces slip through spaces within gels - can travel farther

smaller DNA pieces will appear as a band closer to anode, while larger DNA piece will be further

Question 11

PCR use in Covid testing (5)

Answer 11

swab in nose/throat collects virus RNA

sample rinsed of in saline solution to become liquid

RNA in sample converted to DNA using enzyme reverse transcriptase

PCR amplifies bases sequences which indicate prescence of covid

fluorescent markers attached to produced DNA - if level of fluorescence > target = positive

Question 12

Advantages of PCR in Covid testing

Answer 12

sensitive - viral RNA replicated so miniscule virus contents detected

Question 13

Disadvantages of PCR in Covid testing (2)

Answer 13

expensive equipment

results are not immediately available

Question 14

PCR + gel electrophoresis use in DNA profiling (5)

Answer 14

tandem repeats - short repeated DNA sequences

restriction enzymes chop DNA into fragments (lengths based on number of repeats)

PCR amplifies DNA fragments

DNA fragments then separated using gel electrophoresis

match = same number + length of DNA fragments

Question 15

How are DNA nucleotides held together (2)

Answer 15

phosphodiester bond

bond between phosphate group of 5’ carbon deoxyribose and hydroxyl group of 3’ carbon deoxyribose on next nucleotide

Question 16

Define a phosphodiester bond

Answer 16

occurs when 2 hydroxyl groups in phosphoric acid react with groups in other molecules to form 2 ester bonds

Question 17

Directionality of DNA polymerase

Answer 17

5’ carbon to 3’ carbon

Question 18

Define the DNA leading strand (3)

Answer 18

strand that can be replicated in same direction as helicase (5’ to 3’)

strand has 3’ to 5’ directionality

can be replicated continously (completed quicker)

Question 19

Define the DNA lagging strand (2)

Answer 19

strand that cannot allow DNA polymerase III to move in 5’ to 3’ directionality

strand has 5’ to 3’ directionality

Question 20

DNA strand replication for lagging strand (3)

Answer 20

DNA polymerase III adds nucleotides away from fork movement (opposite to leading)

nucleotides added in sections as replication fork exposes more of template

sections called Okazaki fragments

Question 21

Function of Helicase enzyme in DNA (2)

Answer 21

unwinds DNA molecule by breaking hydrogen bonds between bases

single strand binding proteins attach to single strand of DNA + prevent them from re-forming hydrogen bonds with comp. bases

Question 22

Function of gyrase enzyme in DNA (2)

Answer 22

moves ahead of helicase

relieving tension created by unwinding DNA

Question 23

Function of DNA primase (2)

Answer 23

attaches small RNA primers (RNA nucleotides) to template strand

allows DNA polymerase III to attach to DNA strand

Question 24

Function of DNA polymerase III (2)

Answer 24

places free nucleotides complementary to bases in template strand

only builds new strands in 5’ to 3’ directionality

Question 25

Function of DNA polymerase I

Answer 25

removes RNA nucleotides of primers + replaces with correct DNA nucleotide

Question 26

Function of DNA ligase

Answer 26

catalyses formation of phosphodiester bonds between Okazaki fragments

Question 27

DNA polymerase III in proofreading (2)

Answer 27

proofreads newly formed DNA strand while it is built

nucleotide paired with mismatched base = incorrect nucleotide replaced with correct