Polymerase chain reaction (PCR) - technique that allows scientists to make millions of copies of desired gene fragment in hours

PCR allows scientists to perform genetic testing on incredibly tiny amounts of tissue - even a single cell

PCR can even be used on tissue that has been degraded by environment

Used in medicine, genetics, biotechnology and forensics

Step 1: Denaturation

DNA sample is heated to 94°C - 96°C MUST KNOW TEMPS.

Heating breaks hydrogen bonds that hold double stranded DNA together - result is complimentary single strands

Step 2: DNA primers added (annealing). Cooled to 50 ̊C - 65 ̊C

2 different primers (forward and reverse) - chosen to be complimentary to opposite ends of target region being copied

STEP 3: Taq DNA Polymerase added (Elongation). Heated to 72 ̊C

Taq DNA polymerase comes from bacterium Thermus aquaticus, which is found in hot springs - enzyme does not denature at 72 ̊ C

Taq DNA polymerase joins at primers and moves along strands adding complimentary base pairs as it goes - result is two incomplete copies of DNA, each containing target region

Cycle 1 Complete

STEP 4: Repeat steps 1 - 3

After cycle 2 result is four incomplete copies of DNA, each containing target region

Taq DNA polymerase added; heat to 72 ̊C

Cycle 2

Step 5: Repeat

After the 3rd Cycle, there are a total of 8 DNA copies, 2 of which are target fragments

Cycle 3