Unit 1 Topic 2

Question 1

What must happen before cell division?

Answer 1

DNA replication

Question 2

What two enzymes does DNA replication rely on?

Answer 2

DNA polymerase
DNA ligase

Question 3

Is DNA semi-conservative?

Answer 3

yes

Question 4

What does DNA polymerase do?

Answer 4

adds free DNA nucleotides, using complementary base pairing, to the deoxyribose (3’) end of the new DNA strand which is forming

Question 5

What does DNA ligase do?

Answer 5

joins fragments of DNA together

Question 6

What must be present before DNA replication begins?

Answer 6

a pool of free nucleotides

Question 7

What must be added to DNA to allow DNA polymerase to begin adding free DNA nucleotides?

Answer 7

a primer must be added

Question 8

What is a primer

Answer 8

a short section of nucleotides which binds to the 3’ end of the template DNA strand allowing polymerase to add free DNA nucleotides using the complementary base pairing rule

Question 9

What are the two strands made during DNA replication called and which is made continuously and which is made in fragments?

Answer 9

the leading strand- made continuously
the lagging strand- made in fragments

Question 10

The first step of DNA replication:

Answer 10

DNA is unwound and hydrogen bonds between bases are broken to form two template strands

Question 11

The second step of DNA replication:

Answer 11

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

Question 12

The third step of DNA replication:

Answer 12

on the leading strand, a primer binds to the DNA and DNA polymerase adds free DNA nucleotides to the 3’ end. DNA polymerase catalysed the formation of a chemical bond between nucleotides and continues to add nucleotides to the 3’ end of the growing strand

Question 13

The fourth step of DNA replication:

Answer 13

on the lagging strand, a primer binds to the DNA once it is exposed and DNA polymerase adds nucleotides to the 3’ end. As more DNA is exposed, a new primer is added. DNA polymerase extends the new strand from the primer until it meets the previous fragment. The old promise is replaced by DNA and the enzyme DNA ligase joins the fragments together. As the DNA unzips further, another fragment will be made and connected to the previous one

Question 14

What can PCR be used for?

Answer 14

to amplify a desired DNA sequence of any origin (virus, bacteria, plant or animal) millions of times in a matter of hours

Question 15

Why is PCR especially useful?

Answer 15

it is highly specific
it is easily automated
it is capable of amplifying minute amounts of sample

Question 16

To amplify a target DNA sequence, what components are required?

Answer 16

buffet
nucleotides
primers
Taq polymerase
template DNA

Question 17

What is the role of the buffer?

Answer 17

to keep the reaction mixture at the correct pH to ensure the reaction will proceed

Question 18

Since PCR requires polymerase to operate at high temperatures, what must be used?

Answer 18

Taq polymerase, which is a special type of polymerase which is stable at high temperatures, having an optimum temperature of 70 degrees C

Question 19

What steps must be repeated in PCR?

Answer 19

•the DNA molecule which is to be amplified is denatured by heating to between 92 and 98 degrees C, breaking the hydrogen bonds between base pairs to separate the strands
•the solution is cooled to between 50 and 65 degrees C to allow the primers to anneal to target sequences
•the solution is heated to between 70 and 80 degrees C for heat-tolerant DNA polymerase to replicate the region of DNA

Question 20

How many times is the cycle usually repeated in PCR?

Answer 20

at least 30 times

Question 21

How can PCR be used?

Answer 21

PCR can amplify DNA to help solve crimes, settle paternity suits and diagnose genetic disorders