PCR

Polymerase Chain Reaction (PCR): A Revolutionary Technique in Molecular Biology

Introduction

The Polymerase Chain Reaction (PCR) is a revolutionary molecular technique developed in the 1980s by Kary Mullis. It has dramatically transformed scientific research, forensic science, and diagnostic fields. PCR is a technique used to amplify a specific segment of DNA, generating millions to billions of copies of a particular DNA sequence.

Principle of PCR

PCR is based on the natural process of DNA replication. It involves three main steps: denaturation, annealing, and extension. These steps are repeated in cycles, each cycle doubling the amount of target DNA.

  1. Denaturation: The reaction mixture is heated to 94-96°C. This high temperature breaks the hydrogen bonds holding the two strands of DNA together, resulting in the separation of the DNA double helix into two single strands.

  2. Annealing: The reaction temperature is lowered to 50-65°C. This allows the primers, short pieces of DNA that are complementary to the target DNA sequence, to bind or ‘anneal’ to their complementary sequences on the single-stranded DNA.

  3. Extension: The temperature is raised to 72°C, the optimal temperature for DNA polymerase. This enzyme adds nucleotides to the 3’ end of the primer, extending the DNA chain.

Applications of PCR

PCR has a wide range of applications. In medical diagnostics, it is used to detect the presence of pathogen DNA in patient samples. In forensic science, PCR is used to amplify DNA from crime scene samples for genetic fingerprinting. In research, PCR is used to generate enough DNA for further experiments, such as cloning or sequencing.

Conclusion

In conclusion, PCR is a powerful and versatile tool in molecular biology. It has revolutionized many areas of science by allowing for the rapid and specific amplification of DNA, enabling advancements in research, diagnostics, and forensics. Despite its widespread use, researchers continue to refine the technique and develop new variations to suit specific needs, ensuring that PCR will remain a fundamental technique in molecular biology for years to come.


  1. Cystic Fibrosis:

    • Inheritance Pattern: Autosomal recessive1.

    • Symptoms: Persistent cough, frequent lung infections, wheezing or shortness of breath, poor growth or weight gain, salty-tasting skin.

    • Mutation Location: Chromosome 7.

    • Mutated Gene: CFTR (Cystic Fibrosis Transmembrane Conductance Regulator)1.

  2. Sickle Cell Anemia:

    • Inheritance Pattern: Autosomal recessive.

    • Symptoms: Anemia, episodes of pain, swelling of hands and feet, frequent infections, delayed growth2.

    • Mutation Location: Chromosome 11.

    • Mutated Gene: HBB (Hemoglobin Subunit Beta).

  3. Tay-Sachs Disease:

    • Inheritance Pattern: Autosomal recessive.

    • Symptoms: Decreased muscle tone, loss of motor skills, seizures, red spot on the macula.

    • Mutation Location: Chromosome 15.

    • Mutated Gene: HEXA (Hexosaminidase A).

  4. Parkinson’s Disease:

    • Inheritance Pattern: Mostly sporadic, but can be autosomal dominant or recessive in rare cases.

    • Symptoms: Tremors, slow movement, rigidity, balance problems.

    • Mutation Location: Various chromosomes depending on the gene.

    • Mutated Gene: Various genes can be involved, including LRRK2, PARK2, PARK7, PINK1, SNCA.

  5. Achondroplasia:

    • Inheritance Pattern: Autosomal dominant.

    • Symptoms: Short stature, disproportionately short arms and legs, fingers and toes may appear short and/or fat.

    • Mutation Location: Chromosome 4.

    • Mutated Gene: FGFR3 (Fibroblast Growth Factor Receptor 3).

  6. Phenylketonuria (PKU):

    • Inheritance Pattern: Autosomal recessive.

    • Symptoms: Intellectual disability, seizures, delayed development, behavioral problems, musty odor.

    • Mutation Location: Chromosome 12.

    • Mutated Gene: PAH (Phenylalanine Hydroxylase).

  7. Fibrodysplasia Ossificans Progressiva:

    • Inheritance Pattern: Autosomal dominant.

    • Symptoms: Malformation of the big toes, progressive ossification of soft tissues leading to immobility.

    • Mutation Location: Chromosome 2.

    • Mutated Gene: ACVR1 (Activin A Receptor Type 1).

  8. Harlequin Ichthyosis:

    • Inheritance Pattern: Autosomal recessive9.

    • Symptoms: Severe thickening of the skin, deep cracks, and fissures, distorted facial features.

    • Mutation Location: Chromosome 2.

    • Mutated Gene: ABCA12 (ATP Binding Cassette Subfamily A Member 12)10.