Recording-2025-03-01T17:12:12.894Z

Gene Transfer in Bacteria

Vertical Gene Transfer

• Definition: Genes passed from parents to offspring, e.g. from parents to children.

• Mechanism in Bacteria: Through binary fission, parental cell divides into two daughter cells.

• Result: Offspring have identical genetic material to parents.

Horizontal Gene Transfer (Lateral Gene Transfer)

• Definition: Transfer of genes between bacteria of the same generation (neighbors).

• Importance: Contributes to genetic variability, allowing bacteria to develop new traits, such as antibiotic resistance.

• Mechanisms of Horizontal Gene Transfer:

  • Transformation: Bacteria take up DNA from the environment.

    • Example: A bacterial cell incorporates a plasmid from its surroundings into its genome.

  • Transduction: Transfer of DNA via bacteriophages (viruses that infect bacteria).

    • Example: A bacteriophage injects its genetic material into a bacterium, potentially incorporating bacterial DNA into new phages.

  • Conjugation: Transfer of DNA from one bacterium to another through a conjugation pilus.

    • Example: The F+ donor cell, possessing the F plasmid (fertility factor), forms a pilus to transfer plasmid DNA to an F- recipient cell, leading both to becoming F+.

Conjugation in Detail

• F plasmid (Fertility plasmid): Contains the genetic information necessary to form a conjugation pilus.

• Process of Conjugation:

  1. F+ donor cell connects to F- recipient cell with a pilus.

  2. Genetic material (plasmid DNA) is transferred through the pilus.

  3. The plasmid circularizes and synthesized a complementary strand in the recipient.

  4. Result: Both cells become F+ and can continue transferring plasmids to others.

Significance of Conjugation

• Allows exchange of genes that promote virulence, such as those for toxin and capsule production, and antibiotic resistance.

Transformation

Experiment by Frederick Griffith (1928)

• Organism: Streptococcus pneumoniae (can be encapsulated, virulent, or non-encapsulated, non-virulent).

• Experiment Setup:

  • Control: Rough strain injected into mice → mice survive (non-virulent).

  • Injection of heat-killed smooth strain → mice survive (dead bacteria).

• Unexpected Outcome: Mice injected with a mixture of heat-killed smooth and live rough strains died.

  • Hypothesis: Rough strain incorporated DNA from heat-killed smooth strain, acquiring the virulent trait (capsule formation).

Mechanism of Transformation

• DNA from dead smooth bacteria incorporates into living rough bacteria, altering their genome and allowing them to produce capsules, making them virulent.

Transduction

• Definition: DNA transfer from one bacterium to another via bacteriophages.

Steps:

1. Bacteriophage infects bacterial donor cell, injecting viral DNA.

2. Bacteriophage uses bacterial machinery to replicate itself, sometimes packaging bacterial DNA instead of viral DNA.

3. New bacteriophages released can infect other bacteria, transferring the bacterial DNA.

4. Result: Recipient bacterium becomes recombinant, potentially acquiring new traits.

Gene Regulation in Prokaryotes

Operons

• Definition: A set of related genes controlled together under a single promoter; found in bacteria.

• Key Components of an Operon:

  • Promoter: Site where RNA polymerase binds to initiate transcription.

  • Operator: Site for repressors that block transcription.

  • Structural Genes: Genes that encode proteins facilitating a specific function.

Examples of Operons

TRP Operon (Tryptophan synthesis)

• No tryptophan present: Repressor does not bind, RNA polymerase transcribes genes to produce tryptophan.

• Tryptophan present: Binds to repressor, preventing transcription.

Lac Operon (Lactose metabolism)

• Lactose present: Binds to repressor, allowing transcription of genes for lactose breakdown.

• No lactose: Repressor binds, blocking transcription.

Genetic Engineering

Definition

• Manipulating genetic material to change specific characteristics.

Key Terms

• Recombinant DNA: DNA containing genetic material from different organisms.

• Transgenic: Organisms that have genes transferred from another species.

Genetic Engineering Overview

1. Plasmid Isolation: Extracting plasmid from bacteria.

2. Gene of Interest Extraction: Cutting the gene of interest from another organism’s DNA using restriction enzymes.

3. Insertion: Inserting the gene into the plasmid, making it recombinant.

4. Transformation: Introducing recombinant plasmid back into bacteria.

5. Cloning: Bacteria proliferate, creating a population of cells with the recombinant gene.

Applications of Genetic Engineering

• Medicine: Producing insulin, vaccines, and therapeutic proteins.

• Agriculture: Creating pest-resistant crops using the BT gene from Bacillus thuringiensis.

Tools of Biotechnology

PCR (Polymerase Chain Reaction)

• Technique to amplify DNA.

• Steps:

  1. Denaturation: Heat separates double-stranded DNA (around 95°C).

  2. Annealing: Primers bind to DNA (around 50-65°C).

  3. Extension: DNA polymerase synthesizes complementary strands (around 72°C).

• Result: Exponential amplification of targeted DNA sequence.

CRISPR

• Gene editing technology based on bacterial immune response to viruses.

• Uses RNA and Cas9 protein to make cuts in DNA, allowing for gene insertion or alteration.

• Applications in medical research, such as targeting genetic diseases and enhancing product yields in cells.

Conclusion on Recombinant DNA Technology and Bioproduction

• Field Overview: Use of cells to produce therapeutics and non-medical products.

• Key Areas: Protein therapies, vaccines, biofuels, and genetic modifications in agriculture.

• Importance of ongoing developments and potential in fields of biomedicine and bioengineering.