Polymerase chain reaction (PCR) is a technique for amplifying DNA sequences in vitro. It involves repeated cycles of separating DNA strands through heating and cooling, and using DNA polymerase to make copies of the target sequence. PCR was first proposed in the 1970s and developed in the 1980s by Kary Mullis, who received the Nobel Prize in Chemistry for his work. PCR uses DNA polymerase, primers, nucleotides, and repeated heating and cooling to amplify a specific DNA sequence over a billion-fold, allowing for easy detection and analysis.

1. POLYMERASE CHAIN REACTION
HERA NADEEM

2. HISTORY
•Method was first proposed by H.G Khorana
and colleagues in 1970’s.
•15 years later the idea was independently
conceived by Dr. Kary Mullis in 1983.
•Saiki et al 1988, used the thermostable DNA
polymerase from Thermus aquaticus and
greatly increase the efficiency of PCR.
•In 1989, Science Magazine selected PCR as
the major Scientific development and Taq
DNA polymerase as the Molecule of the year.
•Kary Mullis was awarded Noble prize for
Chemistry in 1993.
Dr. Kary Mullis
Source- wikipedia

3. WHAT IS POLYMERASE CHAIN REACTION ?
A technique for amplifying DNA
sequences in vitro by seperating
the DNA into two strands and
incubating with oligonucleotide
primers and DNA polymerase.
It can amplify a specific
sequence of DNA as many as
one billion times.
Image source: INTERNET

4. BASIC REQUIREMENTS FOR PCR
 DNA Template
 Oligonucleotide Primers
 Taq polymerase
 Deoxyribonucleotides
(dNTPs)
 Buffer solution
 Divalent cations (eg.Mg2+)
 DNA thermal cycler
PCR tube
Image source : internet

5. STEPS INVOLVED IN PCR
The actual technique of PCR involves repeated cycles for
amplification of target DNA. Each cycle has three stages.
I. Denaturation of ds DNA template.
II. Annealing of primers.
III.Extension of ds DNA molecules.

6. I. Denaturation
 Temperature: 92-94℃
 Time : 1minute
 Double stranded DNA melts Single stranded DNA
92℃
3’5’
3’ 5’
+
5’3’
5’ 3’

7. II. Annealing
 Temperature: ~50-70℃
 Time: 1.5 minutes.
 Primers bind to their complementary sequences.
5’
3’
5’ 3’
Forward primer Reverse primer

8. III.Extension
 Temperature: ~72℃.
 Time: 0.5-1.0 minute.
 DNA polymerase binds to the annealed primers and extends
DNA at the 3’ end of the chain.
Taq
5’
3’
Taq5’
5’ 3’
5’

9. Products Of Extension
3’5’
3’ 5’
3’5’
3’ 5’
Taq
Taq

10.  Each cycle of PCR takes about 3-5 minutes.
 In normal practice, the PCR is carried out in an
automated machine, Thermo cycler.
Thermo cycler
Image source : internet