5 (R) OCR

Main Purpose of PCR

To produce enough copies of a DNA sequence so it can be analyzed or used in experiments

PCR Primers

Short single-stranded DNA sequences that provide a starting point for DNA synthesis

Typical Length of PCR Primers

About 20 nucleotides long

Number of Primers Used in PCR

Two primers are used, one for each DNA strand

Function of PCR Primers

They bind to opposite strands and define the DNA region that will be amplified

Key Components of PCR

Template DNA, primers, Taq polymerase, nucleotides, and cofactors

PCR Cycling

Repeated heating and cooling steps used to amplify DNA

Denaturation

The PCR step where DNA strands are separated by heating

Denaturation Temperature

Approximately 96°C

Purpose of Denaturation

To break hydrogen bonds and produce single-stranded DNA templates

Annealing

The PCR step where primers bind to complementary DNA sequences

Annealing Temperature

Typically 55–65°C

Purpose of Annealing

To allow primers to attach to the template DNA

Extension

The PCR step where Taq polymerase synthesizes new DNA strands

Extension Temperature

Approximately 72°C

Result of One PCR Cycle

The number of DNA molecules doubles

Typical Number of PCR Cycles

25–35 cycles

PCR Amplification Pattern

Exponential growth because newly made DNA becomes template in later cycles

Gel Electrophoresis

A technique used to separate DNA fragments based on size

Purpose of Gel Electrophoresis in PCR

To visualize PCR products and determine their size

DNA Ladder

A set of DNA fragments of known sizes used to estimate fragment size

Applications of PCR

Used in cloning, sequencing, diagnostics, and forensic analysis

PCR in Medical Diagnostics

Used to detect genes associated with diseases or pathogens

PCR in Forensics

Used to analyze DNA from crime scenes and compare it to suspects

Genetic Marker

A specific DNA sequence used to identify individuals

Short Tandem Repeats (STRs)

DNA regions with repeating short nucleotide sequences used in forensic analysis

STR Variation

Individuals differ in number of repeat units

Genetic Fingerprint

A unique DNA profile created using multiple STR markers

Typical STR Analysis

Uses about 13 markers to create a DNA profile