chapter 14: dna amplification by polymerase chain reaction
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Chapter 14: DNA Amplification by Polymerase Chain Reaction
Polymerase Chain Reaction (PCR) Copies (“amplifies”)DNA in a test tube
using the same type of chemistry that cells use to copy DNA Exponential amplification of specific, short
(usually 2,000 bp or less) sequences of DNA Products are called amplicons
Highly sensitive Can amplify small quantities Rapid and robust
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Reaction ingredients: PCR Primers
▪ Short, single-stranded DNA polynucleotides that are complementary to the sequences which flank the target region
dNTPs (in abundance) Template DNA DNA Polymerase
▪ Thermostable (e.g. Taq polymerase) MgCl2 and buffer
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PCR steps: Denaturation (94 deg C) Annealing (typically 50-60 deg C)
▪ Set just below melting temperature of primers▪ 4 + 2 rule
Extension (72 deg C)▪ Optimum temp for taq polymerase
Cycling (denaturation, annealing, extension)▪ Typically 20-30 times
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1 copy
2 copies
Repeat 30 times = 230 = 1 billion copies
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PCR controls Used to monitor effectiveness Positive control
▪ Indicates that all reaction ingredients are working
▪ Known sample Negative control
▪ Indicates that there is no contaminating DNA in any of the reaction reagents
▪ Includes all reaction ingredients except template DNA
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Template DNA degradationLow copy number of template
Stochastic EffectPCR inhibitors
Heme, Indigo dyes, Melanin from hairsContamination
Pre-PCR and post-PCR should be in separate areas
Supplies and reagents also separated8
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Activity Cellular Replication
PCR
Denaturation
Primers
Extension
Number of copies produced
Size of region copied
Ingredients
Purpose
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