Lecture 12_250 review

Exam 2 Review Topics

Lecture 12: Gene Transfer

Homologous Recombination

• Definition: A process by which genetic material is exchanged between similar DNA molecules, leading to genetic diversity.

• Function: It is essential for repairing DNA and during meiosis for creating genetic variation in offspring.

Transformation

• Definition: The process by which a cell takes up naked DNA from its environment and incorporates it into its own genome.

  • Competence: The ability of a cell to take up and incorporate external DNA.

    • Natural Competence: Some species have inherent mechanisms to take up DNA (e.g., certain bacteria like Bacillus subtilis).

    • Artificial Competence: Laboratory techniques (e.g., CaCl2 treatment or electroporation) are used to induce competence in cells not naturally competent.

  • Differences Between Gram-negative and Gram-positive:

    • Gram-positive: Generally have simpler cell walls and may utilize transformasomes to facilitate uptake.

    • Gram-negative: More complex cell walls and may require specific competence factors for DNA uptake.

    • Transformasomes: Protein complexes that assist in the transformation process in Gram-positive bacteria.

    • Competence Factors: Proteins that support the uptake of DNA in competent bacteria.

Conjugation

• Definition: A process of direct transfer of genetic material (DNA) from one bacterial cell to another through a physical connection known as a pilus.

  • Differences Between Gram-negative and Gram-positive:

    • Gram-negative: Typically use sex pili to connect and transfer DNA.

    • Gram-positive: May use aggregation substances to facilitate close contact but lack true sex pili.

  • F and F’ Plasmids:

    • F Plasmid: Contains genes for pilus formation and DNA transfer, critical for fertility (F+ cells).

    • F’ Plasmid: A variant of the F plasmid containing some chromosomal genes; allows transfer of both plasmid and chromosomal genes during conjugation.

  • Definitions:

    • F+ Cell: A bacterial cell with an F plasmid, capable of sending genetic material to other cells.

    • F- Cell: A bacterial cell that lacks an F plasmid and cannot initiate DNA transfer.

Transposon

• Definition: A DNA sequence that can change its position within a genome, potentially disrupting genes and altering genetic outcomes.

  • Transposase Role in Transposition: Enzyme that catalyzes the movement of transposons from one location to another in the genome.

  • Occurrence: Found in both eukaryotes and prokaryotes.

Transduction

• Definition: A method of horizontal gene transfer in bacteria where bacteriophages (viruses that infect bacteria) transfer genetic material from one bacterium to another.

  • Role of Bacteriophage: Acts as a vector to facilitate the transfer of DNA, leading to genetic variation and potential antibiotic resistance.