Biology Reference
In-Depth Information
Table 5.1 The PCR reaction can theoretically multiply DNA over
1 billion-fold after 32 cycles; in reality it is not 100% efficient
but is still extremely powerful
Cycle
Number of PCR products
1
0
2
0
3
2
4
4
5
8
6
16
7
32
8
64
9
128
10
256
20
262 144
28 1
67 108 864
30
268 435 456
32 2
1 073 741 824
34 3
4 294 967 296
1 Standard cycle number using Applied Biosystems SGM Plus and Identifiler
Kits.
2 Standard cycle number using Promega PowerPlex 16 Kit.
3 Maximum number of cycles normally used in forensic analysis.
Double-stranded DNA
template molecule
-hydrogen bonds hold
the two strands together
The temperature is increased to 95 ° C. This causes the
hydrogen bonds to break and results in two denatured single-
stranded DNA molecules.
Two single-stranded
DNA molecules
The temperature is reduced to 50
C allowing primers to anneal
to complementary sequences. The two primers must anneal to the
two different strands and must be extended towards each other.
C-60
°
°
Hydrogen bonds stabilize the
template-primer interaction.
The arrow head indicates the
direction of primer extension
The temperature is increased to 72
C. The enzyme Taq polymerase
finds the free ends of the primers (indicated by the arrow heads) and
starts to incorporate nucleotides that are complementary to the
template strand.
°
The end product is two
double-stranded copies of the
template DNA
The PCR reaction - each PCR cycle consists of three phases: denaturing, annealing and
Figure 5.2
extension
 
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