key area 2: replication of DNA

Question 1

State 4 things that must be present for DNA replication

Answer 1

Original DNA template
Free DNA nucleotides
DNA polymerase
Primers

Question 2

Describe the stages of DNA replication

Answer 2

Step 1: hydrogen bonds between the bases break separating the strands
Step 2: free nucleotides start to line up with complementary nucleotides
Step 3: sugar phosphate bonds form . Two DNA molecules identical to the parental molecules have been formed - half the original and half the new copy

Question 3

Replication of the leading strand and lagging strand of DNA

Answer 3

Leading strand
Stage 1: after hydrogen bonds breaks, the DNA unzips
Stage 2: a DNA primer attaches to the start of the piece of DNA being copied
Stage 3: DNA polymerase then attaches free nucleotides to the 3’ end of the primer
For the lagging strand, many primers are attached and are extended by the DNA polymerase and are joined by ligase

Question 4

Describe what a primer is and explain its role in DNA replication

Answer 4

A primer is a short stretch of complementary DNA which allow DNA polymerase to bind

Question 5

Name 2 enzymes involved in DNA replication

Answer 5

DNA polymerase and DNA ligase

Question 6

Role of the enzyme ligase

Answer 6

Joins primers and DNA polymerase together

Question 7

Role of DNA polymerase

Answer 7

Controls the formation of the sugar-phosphate bonds when making new strands

Question 8

Describe the direction of replication on each DNA strand

Answer 8

Starts at the 3’ end and finishes at the 5’ end because DNA polymerase can only attach the 3’ end of a primer

Question 9

Describe the purpose of Polymerase chain reaction (PCR)

Answer 9

Millions of copies of a specific piece of DNA can be created in a few hours in a thermocycler

Question 10

Explain how primers are chosen for a particular PCR

Answer 10

Primers are designed by scientists and can be manufactured by a machine. The sequence for primers can be designed by looking at the published genome sequences

Question 11

Describe the role of heat tolerant DNA polymerase in PCR

Answer 11

Used to synthesis new strands from free DNA nucleotides

Question 12

Describe 3 practical applicants of PCR

Answer 12

DNA profiling- rapidly identify people using specific areas of DNA known to vary between individuals being amplified
Disease detection- indicate certain genetic disorders for the purpose of diagnosis
Archeological analysis- ancient DNA degraded over time can be amplified and used in evolutionary research

Question 13

What is PCR

Answer 13

Polymerase Chain Reaction- allows specific of DNA to be amplified in vitro (replicated out with a cell in a test tube)

Question 14

First cycle of PCR

Answer 14

Stage 1: DNA heated to approximately 90C for a few seconds which causes the DNA to denature and the strands to separate
Stage 2: DNA is cooled to approximately 50-65C for a few seconds which makes short primers to bond to the separated DNA strands
Step 3:DNA heated to 72C for a few seconds to allow heat tolerant DNA polymerase to replicate DNA
Step 4: heat DNA to 95C again
Step 5: cool to between 50 and 65C again which allows primers now to bond to original and new copies
Stage 6: heat to 72C so DNA polymerase copies the DNA again. Process is repeated over and over again

Question 15

PCR controls

Answer 15

Essential to have the correct experimental system to let you verify what you are measuring. You cannot conclude anything concrete from your results unless you have the correct controls in place

Question 16

Negative controls

Answer 16

Contain everything but the template DNA. There should be no amplification of DNA

Question 17

Positive controls

Answer 17

PCR procedure is set up but with a DNA sample which is already known to respond to amplification so any problem with result is due to experimental flaws involving primer, polymerase or the nucleotide supply