Transcript PCR Polymerase Chain

PCR
Polymerase Chain
Reaction
What is it and how is it useful?

A quick, easy method for amplifying (creating
billions of copies) of unimaginably tiny amounts of
DNA

Methodology closely related to process of DNA
replication

Used in forensic science to analyze small quantities
of DNA recovered from a crime scene such as:
- saliva on a cigarette butt or envelope
- DNA in the root of a single strand of hair
- tissue under the fingernails of a victim
- DNA in a single drop of blood
- a small semen stain

Used to detect disease/infection in an
organism and treat it before a condition
worsens

Anthropology/archeology – PCR has
allowed tiny fragments of DNA that
have been exposed and degraded over
thousands of years to be amplified and
studied
How does PCR work?
Need:
• The DNA molecule you
want to copy ( the
template)
• 2 DNA primer
molecules – short,
single stranded chains
of nucleotides that
attach to the “unzipped
DNA”
• DNA polymerase
• A system for heating
and cooling the DNA
strands
The Steps…..

1. DNA molecule separated by heating the sample
to 90-96 °C

2. Strands are cooled so that DNA primers can be
added. Primers bind to complementary bases on
the two separated strands of DNA.

3. A special DNA polymerase (Taq polymerase)
reads the template strand and matches it with
complementary nucleotides found within the DNA
suspension (test tube)
Note: Taq polymerase comes from Thermus aquaticus
– a type of bacteria that lives in hot springs
END RESULT – 2 new helixes each made up of one of
the original strands plus a newly assembled
complementary strand
Each subsequent cycle doubles the # DNA molecules
copied – exponential increase
Ex: 30 cycles – 230 DNA copied
Each cycle takes 1-3 minutes. Therefore, in 1 hour you
can have over a billion strands of a specific DNA
molecule