DNA Technology

DNA Technology Lecture Notes

I. Polymerase Chain Reaction (PCR)

A. Introduction to PCR

  • PCR - Polymerase Chain Reaction

  • Problem Addressed:

    • Often insufficient DNA available for testing.

  • PCR Functionality:

    • Produces billions of copies of DNA in a short period.

    • Modeled after the natural process of DNA replication.

  • Components Required for PCR:

    • dNTPs:

    • Deoxyribonucleotides (Adenine (A), Thymine (T), Cytosine (C), Guanine (G)).

    • Primers:

    • Short DNA fragments (15-20 base pairs) with specific sequences.

    • Taq Polymerase:

    • DNA polymerase derived from Thermus aquaticus, a bacterium found in hot springs at Yellowstone National Park.

  • Method of DNA Amplification:

    • A 3-step process repeated for 30-40 cycles:

    1. Denaturation

    2. Annealing

    3. Extension

    • Conducted in a thermal cycler in laboratory settings.

B. Process of PCR

  • Step 1 - Denaturation:

    • Temperature Requirement:

    • Heat DNA to over 90 degrees Celsius.

    • Outcome:

    • Breaks hydrogen bonds, separating DNA strands.

  • Step 2 - Annealing:

    • Temperature Range:

    • 40 degrees Celsius to 65 degrees Celsius.

    • Outcome:

    • Two DNA primers anneal specifically to the 3’ side of the DNA strands.

    • At the end of the first cycle, two new DNA strands are formed.

  • Cycle Impact:

    • After several cycles, the amplification can reach factors of $10^6$ to $10^9$.

C. PCR Challenges

  • Although PCR seems straightforward (set up, run, and retrieve DNA), the process is nuanced.

    • Challenges:

    • Almost every step can potentially fail and will fail if not handled meticulously.

    • Molecular techniques are highly sensitive to conditions and can be easily contaminated.

II. Gel Electrophoresis

A. Overview

  • Definition:

    • Gel electrophoresis is a technique for separating nucleic acids based on their size.

  • Common Usage:

    • Frequently employed to confirm results of PCR.

  • Components:

    • Gel Medium:

    • Polyacrylamide Gel (also Agarose, a polysaccharide).

    • Electrical Current:

    • An electric current is passed through the gel, allowing DNA to migrate.

    • DNA moves from negative to positive electrodes because DNA is negatively charged.

B. Uses of Gel Electrophoresis

  • PCR Verification

  • DNA and RNA Analysis

  • Gene Cloning and Sequencing

  • DNA Mutation Detection

III. Applications of DNA Technology

A. DNA Sequencing

  • Methodology:

    • Chain termination sequencing is employed.

    • This method follows a process similar to PCR followed by gel electrophoresis.

  • Fragment Generation:

    • Produces fragments of different sizes from the original template.

  • Separation Technique:

    • Gel electrophoresis is used to separate fragments by size, which are then analyzed in order of size.

B. Species Diversity

  • Purpose:

    • Utilized to identify various species within a community.

  • Applications:

    • Effective for identifying rare, mobile, difficult-to-identify, or microscopic species.

    • Use of barcoding for species identification.

  • Example of Barcoding:

    • Barcode sequences represented as: IIIIIIIIIIIIIIII or 012345789012.

  • Relevance in Research:

    • Important for population genetics, conservation, phylogenetic studies, and evolutionary research.

    • Assists in identifying organisms with similar appearances, such as insect larvae and worms.

C. Gene Therapy

  • Application:

    • Used to address a specific type of genetic blindness.

  • Methodology:

    • Employs a retrovirus to insert corrected genes into retinal cells.

  • CRISPR Technology:

    • Tools for gene therapy include CRISPR technology for gene silencing and insertion.

    • Specific applications include gene silencing with CRISPR and gene insertion techniques utilizing CRISPR.