Genetic Technologies: Recombinant DNA, Plasmids, and Applications

Genetic Technologies

Introduction

Genetic technologies involve the manipulation of DNA and genes to produce useful products, diagnose diseases, and advance biotechnology. These techniques are foundational in modern biology and medicine, allowing scientists to clone genes, produce therapeutic proteins, and develop vaccines.

Recombinant Plasmids

Biotechnology and DNA Manipulation

• Biotechnology is the manipulation of organisms or their components to create products that are useful for society.

• Modern DNA technology enables the transfer and expression of genes of interest between different organisms.

• Recombinant DNA is formed when two pieces of DNA, often from different species, are combined to create a single DNA molecule.

• This process allows for the mass production of proteins, which can be used therapeutically (e.g., vaccines).

• Example: Combining E. coli and human genes to produce insulin.

Bacterial Plasmids as Tools

• Plasmids are small, circular DNA molecules that replicate independently of the bacterial chromosome.

• They are commonly used to clone genes because they can carry any bacterial gene and are passed on during DNA replication.

• Gene cloning refers to the mass production of identical copies of a single piece of DNA.

• Genetic engineering is the practical manipulation of genes for specific purposes.

Steps in Producing Recombinant Proteins

1. A bacterial plasmid is isolated to serve as a vector for the gene of interest.

2. The gene of interest can originate from various sources (bacteria, plants, etc.).

3. A specific restriction enzyme is chosen to cut the plasmid at a single site.

4. The gene source is treated with an enzyme that cuts the DNA in more than one place, producing fragments that include the gene of interest.

5. The cut DNA from both the plasmid and the source are mixed; single-stranded ends base pair with complementary ends.

6. DNA ligase enzyme joins the DNA fragments by forming covalent bonds between adjacent nucleotides, creating recombinant DNA.

7. The recombinant plasmids are mixed with a bacterial culture under conditions that allow bacteria to take up the plasmids (transformation).

8. The recombinant bacteria reproduce, each containing the recombinant plasmid and the gene of interest.

Enzymes that Cut & Paste DNA

Restriction Enzymes

• Restriction enzymes are bacterial enzymes that cut DNA at specific nucleotide sequences called restriction sites (usually 4-8 nucleotides long).

• These enzymes protect bacteria from foreign DNA by cleaving it.

• Examples:

  • EcoRI (from E. coli) recognizes the sequence GAATTC.

  • BamHI recognizes the sequence GGATCC.

• Upon recognition, the enzyme cuts both DNA strands at the restriction site, often producing sticky ends (single-stranded overhangs).

Gene Cloning Procedure

1. A DNA fragment containing the restriction site is cut by the restriction enzyme, producing restriction fragments with sticky ends.

2. The external DNA (gene of interest) is also cut with the same enzyme, ensuring compatible sticky ends.

3. The complementary sticky ends of the plasmid and gene fragment base pair.

4. DNA ligase seals the nicks, forming covalent bonds and creating recombinant DNA.

5. This completes the gene-cloning procedure, resulting in a plasmid carrying the gene of interest.

Mass Production of Gene Products

Manufacturing Proteins Using Genetic Techniques

• Recombinant plasmids are introduced into yeast or bacteria, which replicate and mass-produce the protein of interest.

• The protein is harvested and purified for industrial or medical use.

• Mammalian cells are sometimes used to produce proteins that require specific modifications, such as glycosylation (addition of sugar groups).

• In these cases, the gene of interest is added to a vector and taken up by mammalian cells for production.

Table: Examples of Recombinant Proteins Produced by Genetic Technologies

Protein	Source Organism	Therapeutic Use
Insulin	E. coli, yeast	Diabetes management
Human Growth Hormone (HGH)	E. coli	Treatment of dwarfism
Tissue Plasminogen Activator (TPA)	Mammalian cells	Treatment of heart attacks
Factor VIII	Mammalian cells	Treatment of hemophilia
Hepatitis B surface antigen	Yeast	Vaccine production
Additional info: Other proteins include interferons, clotting factors, and enzymes for metabolic disorders.

DNA Technologies: Applications

Therapeutic Hormones

• Insulin is required to manage diabetes; recombinant DNA technology allows production of human insulin in bacteria.

• Prior to recombinant technology, insulin was extracted from cattle and pigs, which could cause side effects due to chemical differences.

• Recombinant human insulin was the first DNA product approved for human use by the FDA.

Human Growth Hormone (HGH)

• HGH is essential for normal growth; deficiency leads to dwarfism.

• Recombinant DNA technology enables production of synthetic HGH in E. coli.

• Only the human form is effective; previously, HGH was extracted from cadavers.

Tissue Plasminogen Activator (TPA)

• TPA is administered after heart attacks to dissolve blood clots and reduce risk of subsequent attacks.

• Produced using recombinant DNA technology.

Diagnosis and Treatment of Disease

• DNA technology is used to diagnose genetic diseases such as:

  • Sickle-cell disease

  • Hemophilia

  • Cystic fibrosis

  • Huntington's disease

• Individuals and carriers can be identified before symptoms appear or even before birth.

• Viral diseases (e.g., HIV) can be detected using DNA technology before traditional tests are effective.

Vaccines

• Genetically engineered cells or pathogens can be used to produce large amounts of protein for vaccines.

• Proteins from virus or bacterial surfaces are injected to stimulate an immune response.

• Immunity is conferred without exposure to the actual pathogen.

• Mutant bacteria or viruses with key genes knocked out can be used as vaccines; they induce a strong immune response but cannot cause severe disease.

• Example: Hepatitis B vaccine is produced using recombinant technology.

Additional info: Recombinant DNA technology is also used in agriculture, forensic science, and environmental monitoring.