PCR
Definition
Polymerase Chain Reaction. Kary Mullis 1983. Exponential amplification of a target sequence using a thermostable Taq polymerase, two primers and thermal cycling.
- Full name
- Polymerase Chain Reaction
- Inventor
- Kary Mullis, 1983
- Mechanism
- Exponential amplification via thermostable Taq polymerase, two primers, thermal cycling
Common questions
Why does thermal cycling let PCR amplify DNA exponentially rather than linearly?+
Each cycle of heating and cooling denatures the double strands, anneals the primers, and extends new complementary strands, and because every new strand made also serves as a template in the next cycle, the target sequence doubles roughly each cycle rather than accumulating one copy at a time.
Why was a thermostable polymerase necessary for PCR to work as an automated process?+
Early amplification methods used a polymerase that denatured at the high temperatures needed to separate DNA strands, requiring fresh enzyme every cycle. Taq polymerase, isolated from a heat-tolerant bacterium, survives repeated heating, which let the whole process run automatically in a thermal cycler.
Related terms
- Autosomal vs Mitochondrial DNA
- Autosomal DNA is nuclear, biparentally inherited, present as two copies per cell. Mitochondrial DNA is cytoplasmic, maternally inherited, present in hundreds to...
- Capillary Electrophoresis
- Size separation of fluorescently labelled PCR products through a polymer-filled capillary on an instrument like the ABI 3500. Output is an electropherogram.
- Chromosome
- A discrete, condensed structure consisting of a single long DNA molecule complexed with histone proteins. Humans normally carry 46 chromosomes in 23...
- CODIS
- The FBI's Combined DNA Index System, the US national STR-based forensic DNA database. Contains profiles from convicted offenders, arrestees, and unidentified crime-scene...
- Multiplex STR Kit
- Single-tube PCR amplifying 15+ STR loci plus amelogenin in one reaction. AmpFISTR Identifiler Plus and PowerPlex are the workhorses in Indian DNA...
- Nucleotide
- The monomer unit of nucleic acids. Each nucleotide consists of a five-carbon sugar (deoxyribose in DNA, ribose in RNA), a phosphate group,...
- RFLP
- Restriction Fragment Length Polymorphism. The first-generation DNA typing method using restriction enzymes and Southern blotting. Required nanograms of intact DNA.
- SNP (Single Nucleotide Polymorphism)
- A position in the genome where the nucleotide base differs between individuals. Genome-wide SNP panels are more powerful than STR panels for...
- STR (Short Tandem Repeat)
- A genomic locus where a 2, 7 base-pair unit is repeated in tandem a variable number of times between individuals. The variation...
- VNTR
- Variable Number Tandem Repeats. Longer repeat units (10 to 100 bp) than STRs. The original Alec Jeffreys 1984 fingerprinting markers, now superseded...
- Watson-Crick Base Pairing
- Adenine pairs with thymine via two hydrogen bonds; guanine pairs with cytosine via three. The pairing rule that makes the double helix...