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Key Experiments with Streptococcus pneumoniae

Overview of Experiments

  • Experiment 1: Injected rough strain (non-virulent) into mouse.

    • Result: Mouse survives.

  • Experiment 2: Injected heat-killed smooth strain (virulent but dead) into mouse.

    • Result: Mouse survives (dead bacteria cannot cause illness).

  • Experiment 3: Injected live smooth strain into mouse.

    • Result: Mouse dies (virulent encapsulated bacteria).

  • Experiment 4: Injected rough strain and heat-killed smooth strain into mouse.

    • Result: Mouse dies, indicating genetic transformation.

Genetic Transformation

  • Mechanism: Rough strain incorporates DNA from heat-killed smooth strain.

    • Heat-killed bacteria break open, releasing DNA fragments.

    • Rough strain takes up DNA fragments containing capsule production gene.

    • Result: Rough strain becomes virulent due to acquisition of capsule production genes.

Mechanisms of Horizontal Gene Transfer

Three Mechanisms

  1. Transformation: Uptake of naked DNA from the environment.

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

    • Donor bacteria infected by bacteriophage can package bacterial DNA instead of viral DNA.

    • New recipient bacteria can incorporate this DNA, resulting in genetic recombination.

  3. Conjugation: Direct transfer of DNA between bacteria through contact (not discussed in depth in the transcript).

Transduction Process

  • Viruses attach and inject their DNA into bacterial cells.

  • Bacteria replicate the viral DNA, occasionally using bacterial DNA instead.

  • Re-packaged viruses can then infect new bacteria, transferring the bacterial DNA.

  • Result: Recipient bacteria obtain DNA that might confer new traits.

Gene Regulation in Prokaryotes

Gene Expression Control

  • Prokaryotes regulate gene expression to conserve energy, involving mechanisms distinct from eukaryotes.

  • Operons: Groups of related genes regulated as a unit, composed of:

    • Promoter: RNA polymerase binding site for transcription initiation.

    • Operator: Binding site for repressors to inhibit transcription.

    • Structural genes: Genes coding for proteins related in function.

TRP Operon Example

  • Regulates tryptophan biosynthesis:

    • No tryptophan: Repressor does not bind, transcription occurs.

    • Presence of tryptophan: Binds to the repressor, blocking transcription.

Lac Operon Example

  • Controls lactose metabolism:

    • With lactose: Repressor is inactive, transcription occurs for enzymes to metabolize lactose.

    • Without lactose: Repressor binds, blocking transcription.

Genetic Engineering

Overview

  • Manipulation of genetic material to change specific traits.

  • Recombinant DNA technology: Combination of DNA from different organisms.

    • Key techniques include transformation and cloning.

Cloning Process

  1. Isolate plasmid from bacteria.

  2. Extract gene of interest from another organism's DNA.

  3. Use restriction endonucleases to cut DNA at specific sites.

  4. Insert gene of interest into plasmid and reintroduce it into bacterial cells (now recombinant).

  5. Clone bacteria to produce multiple organisms carrying the new gene or protein.

Applications of Genetic Engineering

Medical Applications

  • Production of therapeutics such as:

    • Insulin: Made from recombinant DNA in bacteria instead of pigs.

    • Interferon: Helps treat viral infections and cancers.

    • Vaccines: Examples include subunit vaccines like the hepatitis B vaccine.

    • Gene therapies: Under research to treat genetic disorders.

Industrial and Agricultural Applications

  • Examples include enhancing crop resistance (e.g., Roundup-resistant crops) and improving bioremediation efforts using modified bacteria.

Tools of Biotechnology

Polymerase Chain Reaction (PCR)

  • Technique used to amplify small DNA samples.

  • Works through repeated cycles of:

    1. Denaturation (95°C): Separates DNA into single strands.

    2. Annealing (55-65°C): Primers bind to DNA.

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

  • Exponential growth of DNA allows for detailed analysis.

CRISPR Technology

  • Gene editing technique derived from bacterial immune systems against viruses.

  • Uses guide RNA to target specific DNA sequences and programmed Cas9 protein to cut DNA, facilitating gene editing.

  • Applications in research, agriculture, and potential medical treatments, such as targeting diseases at the genetic level.

Conclusions

  • Gene regulation, horizontal gene transfer, and genetic engineering are foundational concepts in microbiology, with extensive applications in medicine, industry, and more. Emphasizing the need to understand these processes for future advancements in biotechnology.