Week 9 - Nov 3&5

DNA Technology and Biotechnology

Introduction to Biotechnology

Biotechnology is the application of biological systems or living organisms to develop or modify products or processes for specific purposes. DNA technology is a subset of biotechnology focused on manipulating DNA to serve scientific, medical, or industrial goals.

• Biotechnology: Any technique that uses living organisms or their systems to make or modify products.

• DNA Technology: Techniques for isolating, purifying, analyzing, and manipulating DNA.

• Genetic Engineering: The direct modification of genes or genomes for practical applications.

• Example: The first genetically engineered drug was insulin, produced by inserting the human insulin gene into Escherichia coli bacteria.

Model Organisms in Biotechnology

Role of Escherichia coli

Model organisms like Escherichia coli (E. coli) are essential for developing and testing biotechnology tools due to their rapid growth and well-understood genetics.

• E. coli: A common bacterium used in genetic engineering and molecular cloning.

• Allows for efficient manipulation and expression of foreign genes.

DNA Structure and Denaturation

DNA Structure and Base Pairing

DNA consists of two antiparallel strands forming a double helix, stabilized by hydrogen bonds between complementary bases.

• Base Pairing: Adenine (A) pairs with Thymine (T); Guanine (G) pairs with Cytosine (C).

• Hydrogen Bonds: Hold the two DNA strands together.

Denaturation (Melting) of DNA

High temperatures can disrupt hydrogen bonds, causing the double helix to separate into single strands (denaturation).

• Melting Temperature (Tm): The temperature at which 50% of DNA molecules are single-stranded.

• Denaturation is essential for techniques like PCR.

Bacterial Plasmids and Restriction Enzymes

Bacterial Plasmids

Plasmids are small, circular DNA molecules found in bacteria, separate from chromosomal DNA. They often carry non-essential genes and can replicate independently.

• Plasmids: Used as vectors to carry foreign genes in genetic engineering.

• Passed to daughter cells during cell division.

Restriction Enzymes

Restriction enzymes are proteins produced by bacteria and archaea to defend against viruses by cutting foreign DNA at specific sequences.

• Recognition Sites: Short, palindromic DNA sequences recognized by restriction enzymes (e.g., EcoRI recognizes GAATTC).

• Sticky Ends: Single-stranded overhangs created by staggered cuts, facilitating the joining of DNA fragments.

Recombinant DNA Technology

Creation of Recombinant DNA

Recombinant DNA is formed by joining DNA from two different sources, often using restriction enzymes and DNA ligase.

• Cut both the plasmid and the gene of interest with the same restriction enzyme to create complementary sticky ends.

• Ligase enzyme joins the DNA fragments, forming recombinant plasmids.

• Example: Human insulin gene inserted into a plasmid and expressed in E. coli.

Transformation

Transformation is the process of introducing recombinant DNA into bacterial cells, where it can replicate and express the gene of interest.

• Bacteria take up recombinant plasmids and propagate them, producing multiple copies of the gene.

Key Features of Laboratory Plasmids

Feature	Function
Origin of Replication (ORI)	Allows plasmid replication in host cells
Selectable Marker	Enables identification of cells with plasmid (e.g., antibiotic resistance)
Promoter	Drives expression of inserted gene
Multiple Cloning Site (MCS)	Contains many restriction sites for gene insertion

Agarose Gel Electrophoresis

Principle and Application

Agarose gel electrophoresis separates DNA fragments by size using an electric field. DNA moves toward the positive electrode, with smaller fragments migrating faster.

• Used to analyze DNA fragments after restriction digestion or PCR.

• Visualizes DNA using stains that bind to nucleic acids.

DNA Cloning Techniques

Molecular Cloning

Molecular cloning involves inserting a gene of interest into a plasmid vector, transforming bacteria, and allowing them to replicate the gene.

• Gene is transcribed and translated in bacteria, enabling protein production (e.g., insulin).

Polymerase Chain Reaction (PCR)

PCR is a technique to amplify a specific DNA sequence exponentially using cycles of heating and cooling.

• Components: Template DNA, primers, DNA polymerase (usually Taq polymerase), and dNTPs (deoxynucleotide triphosphates).

• Primers: Short DNA sequences that flank the target region and provide starting points for DNA synthesis.

Major Stages of PCR

1. Denaturation: DNA is heated to ~95°C to separate strands.

2. Primer Annealing: Temperature is lowered (50–65°C) to allow primers to bind to complementary sequences.

3. Extension: DNA polymerase synthesizes new DNA at ~72°C.

These steps are repeated 20–30 times, doubling the amount of target DNA each cycle:

$2^n$ Where n is the number of cycles. $2^{10} = 1 \times 10^3$ $2^{20} = 1 \times 10^6$ $2^{30} = 1 \times 10^9$

Checking PCR Success

The success of PCR amplification is typically verified by agarose gel electrophoresis, which shows bands corresponding to the expected size of the amplified DNA fragment.

Applications: Insulin Production

Genetically Engineered Insulin

Human insulin is produced by inserting the human insulin gene into bacteria, which then synthesize the protein. The process involves:

• Isolating the insulin gene from human DNA.

• Inserting the gene into a plasmid vector.

• Transforming bacteria with the recombinant plasmid.

• Growing bacteria in fermentation tanks to produce insulin.

• Purifying insulin for medical use.

Historical Note: The first recombinant human insulin was produced by Eli Lilly in 1983 and approved by the FDA in 1990.

Summary Table: Key Tools in DNA Technology

Tool/Technique	Purpose	Example/Application
Restriction Enzymes	Cut DNA at specific sequences	EcoRI cuts at GAATTC
Plasmid Vectors	Carry foreign genes into host cells	Production of insulin in E. coli
DNA Ligase	Joins DNA fragments	Formation of recombinant DNA
Agarose Gel Electrophoresis	Separates DNA by size	Analyzing PCR products
PCR	Amplifies specific DNA sequences	Genetic testing, cloning

Additional info: These notes cover foundational concepts in DNA technology, including the molecular tools and laboratory techniques essential for genetic engineering and biotechnology. Understanding these principles is critical for advanced studies in genetics, molecular biology, and biotechnology applications.