PCR

Question 1

what does PCR stand for

Answer 1

polymerase chain reaction

Question 2

what is PCR

Answer 2

a version of the natural process of DNA replication where amplifying DNA allows a tiny sample of DNA to produce a lot of DNA

Question 3

what is a PCR machine calle

Answer 3

a thermal cycler

Question 4

what is mixed and added to the vial in the thermal cycler

Answer 4

• the DNA sample to be amplified
• excess of the 4 nucleotide bases ATCG (in the form deoxynucleoside triphosphates)
• small primer DNA sequences
• enzyme DNA polymerase

Question 5

what is controlled in a thermal cycler

Answer 5

• the temperature
• changes rapidly at programmed intervals, triggering different stages of the process

Question 6

can the reaction be repeated in the thermal cycler?

Answer 6

• yes, many times
• it cycles through the programmed temperature settings
• about 30 repeats gives around 1 billion copies of the og DNA sample (more than enough to carry out DNA profiling)

Question 7

PCR stages

Answer 7

• separation
• annealing
• synthesis

Question 8

PCR stage 1

Answer 8

• separating the strands
• temp is increased to 90-95 for 30 seconds
• denatures DNA by breaking the H bonds holding the strands together so they separate

Question 9

PCR stage 2

Answer 9

• annealing of the primers
• temp is decreased to 55-60 and primers bind/anneal to ends of DNA strands
• needed for the replication of the strands to occur

Question 10

PCR stage 3

Answer 10

• synthesis of DNA
• temp is increase to 72-75 for at least 1 min
• optimum temp for DNA polymerase to work best
• DNA polymerase adds bases to the primer, building up complementary strands of DNA and so producing double stranded DNA identical to the og sequence
• Taq polymerase is used, obtained from thermophilic bacteria in hot springs

Question 11

uses of DNA profiling

Answer 11

• forensic science- solving crimes where only tiny amounts of DNA are available (so PCR is used)
• DNA traces obtained from blood, semen, saliva, hair roots and skin cells and compared to sample taken from suspect/database
• proving paternity of child
• immigration cases to prove/disprove family relationships
• identifying species an organism belongs to
• demonstrating evolutionary links between species
• identifying individuals at risk of diseases e.g. identifying marker genes associated with diseases