1.2 Replication of DNA

Question 1

What is ‘DNA Replication’?

Answer 1

Process by which the Cell makes an identical copy of their DNA at the beginning of each cell division

Question 2

Why is DNA replication important?

Answer 2

Ensures each daughter cell has an IDENTICAL copy of genetic material inherited from parent cell and NO GENETIC INFORMATION IS LOST

Question 3

What are the key requirements for DNA Replication?

Answer 3

• DNA Polymerase
• Template DNA strand
• Primer
• Ligase
• ATP
• Free DNA nucleotides

Question 4

What is the function of DNA Polymerase in replication

Answer 4

Adds free complementary nucleotides to the parent strand starting at 3’ end and forms strong chemical bonds between phosphate and sugars of DNA strand.

Question 5

Why is an original DNA strand needed?

Answer 5

To provide the template to be copied

Question 6

What is a primer?

Answer 6

A short sequence of DNA nucleotides that initiates replication and allows DNA polymerase to start adding nucleotides

Question 7

What is Ligase used for in DNA replication?

Answer 7

Joins together the DNA fragments

Question 8

Why is ATP needed in DNA replication?

Answer 8

To provide energy to break the bonds between bases when DNA is being unwound

Question 9

State the steps in DNA replication

Answer 9

1. DNA is unwound, hydrogen bonds break between bases and a replication fork is formed
2. A primer is added to a complementary sequence at the 3’ end
3. DNA polymerase comes along and starts adding free complementary nucleotides to the 3’ end, and DNA Polymerase forms a strong sugar phosphate bond between nucleotides
4. Replication is continuous on the leading strand but discontinuous on the lagging strand due to the antiparallel nature of DNA
5. DNA fragments are joined together by Ligase and hydrogen bonds form between bases

Question 10

What are the two strands in DNA replication?

Answer 10

Leading strand and Lagging Strand

Question 11

Describe the replication of the lagging strand

Answer 11

Discontinuous due to antiparallel nature of DNA
DNA fragments are formed
Fragments must be glued together by Ligase

Question 12

What side can new nucleotides be added to?

Answer 12

3’

Question 13

What glues DNA fragments together?

Answer 13

Ligase

Question 14

What does PCR stand for?

Answer 14

Polymerase Chain Reaction

Question 15

What is PCR?

Answer 15

PCR is the amplification of DNA sequences in vitro by thermocycling

Question 16

What is thermocycling?

Answer 16

Repeated heating and cooling cycles

Question 17

What are the three temperatures needed for PCR?

Answer 17

94 degrees
55 degrees
72 degrees

Question 18

Why must DNA be heated to 94 degrees?

Answer 18

To denature the DNA, separating the strands and breaking the hydrogen bonds

Question 19

What happens when the DNA is cooled to 55 degrees?

Answer 19

Allows primers to anneal to target sequences in DNA

Question 20

At 72 degrees what is added?

Answer 20

Taq Polymerase (Heat tolerant Polymerase)

Question 21

Why is Taq (Heat tolerant) Polymerase used in PCR?

Answer 21

Because it is able to withstand high temperatures (like 72 degrees) without being denatured

Question 22

Why are two different primers required in PCR?

Answer 22

• Two strands of DNA

- Two specific complementary sequences that must be found

Question 23

How is DNA separated?

Answer 23

Using gel electrophoresis

Question 24

Give an example of a practical use of PCR

Answer 24

Paternity Testing
Forensics
Evolutionary Study

Question 25

What is a positive control for PCR?

Answer 25

Doing PCR with a known sample of DNA, expected result is known

Question 26

What does a PCR allow the scientist to prove?

Answer 26

PCR equipment is not contaminated

Question 27

What is a negative control for PCR?

Answer 27

Doing PCR with a key factor missing (such as removal of DNA Polymerase) to prove no contamination

Question 28

If the scientist did X cycles of PCR, how many copies of DNA would they expect to find

Answer 28

2^x

Question 29

If a scientist did 5 cycles of PCR, how many copies of the DNA would they have

Answer 29

32

Question 30

Describe the direction of replication on the lagging strand

Answer 30

3’ to 5’