Bacterial Variation Types
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Questions and Answers

What are transposons and why are they referred to as 'jumping genes'?

Transposons are movable genetic elements that are incapable of independent replication and can jump or transpose to a cell's chromosome or plasmid.

What is the primary difference between insertion sequences (IS) elements and transposons (Tn)?

IS elements are the simplest type of transposable elements, whereas transposons are larger and carry additional genes, such as those for antibiotic resistance.

Why must transposons be integrated with the chromosome or plasmid of the host cell?

Transposons must be integrated with the chromosome or plasmid because they are incapable of independent replication.

How can integration of transposons into host DNA potentially affect the host's genetic structure?

<p>Integration of transposons into host DNA may modify gene expression or produce chromosomal mutations.</p> Signup and view all the answers

What critical role do transposases play in the function of transposons?

<p>Transposases are enzymes that move DNA directly to a new position, enabling the transposition activity of transposons.</p> Signup and view all the answers

Describe one potential benefit of transposons in bacteria.

<p>One potential benefit is that transposons can carry genes that confer antibiotic resistance, aiding bacterial survival in the presence of antibiotics.</p> Signup and view all the answers

What are inverted repeats and where are they found in transposons?

<p>Inverted repeats are sequences of nucleotides that are identical but run in opposite directions; they are found at both ends of transposons.</p> Signup and view all the answers

Which genes do transposons typically carry, and how are these genes non-essential for bacteria's basic survival?

<p>Transposons typically carry genes that are not essential for basic survival, such as antibiotic resistance genes.</p> Signup and view all the answers

How do transposons contribute to genetic diversity in bacterial populations?

<p>Transposons contribute to genetic diversity by causing mutations and rearranging the genome when they integrate into new positions.</p> Signup and view all the answers

What effect can the integration of transposons have on the expression of nearby genes?

<p>The integration of transposons can modify the expression of nearby genes by altering regulatory elements or disrupting gene sequences.</p> Signup and view all the answers

Study Notes

Bacterial Variation

  • Definition: Temporal or permanent changes in bacterial general characters during rapid growth and multiplication.
  • 2 Types:
    • Phenotypic variation
    • Genotypic variation

Phenotypic Variation

  • Cause: Adaptation of bacteria to external conditions, activating genes and leading to temporal changes in bacterial characters.
  • Characters: Changes are usually reversible, unstable, and non-heritable.
  • Examples:
    • Spore formation
    • Change in pigment production

Genotypic Variation

  • Cause: Modification of a character due to changes in genes caused by mutations or gene transfer, leading to permanent changes in bacterial characters.
  • Characters: Changes are heritable, permanent, irreversible, and stable.
  • Consequences:
    • Non-functional genes
    • Acquiring functional genes with appearance of new characters, such as:
      • Antibiotic resistance
      • Toxin production

Bacterial Genetics

  • Advantages of studying bacterial genetics:
    • Discovery of mechanisms of antimicrobial drug resistance
    • Facilitation of genetic engineering
  • Bacteria have:
    • Chromosomal and extra-chromosomal genetic elements
    • Ability of horizontal transfer
    • High rate of division

Genome

  • Definition: Genetic material and information in a cell, including chromosomes and plasmids.
  • Chromosomes: Structures containing DNA that physically carry hereditary information, containing genes.
  • Genes: Functional segments of DNA that code for functional products.

Mutation

  • Definition: Genotypic variation due to change in the sequence of bases in the DNA, either by substitution, deletion, or insertion of bases.
  • Characters:
    • Spontaneity: Natural
    • Discontinuity: Sudden
    • Rarity: Infrequent, but rate increases with exposure to mutagens
    • Stability: Inherited
  • Types:
    • Substitutions
    • Deletions
    • Insertions
    • Inversions

Genetic Transfer

  • Definition: Genotypic variation due to transfer of genes, either within the cell (transposition) or between cells (conjugation, transduction, and transformation).
  • Types:
    • Transformation
    • Transduction
    • Conjugation

Importance of Genetic Transfer

  • To organisms: As indicated below
  • To research: As a vector for transferring genes into cells

Types of Plasmids

  • According to function:
    • Fertility factor plasmids (F plasmid): Carry genes for transfer to another bacterium via conjugation
    • R plasmids: Carry drug resistance genes
    • Col plasmids: Carry genes for bacteriocins
    • Virulence plasmids: Carry virulence genes, e.g. toxin production
  • According to structure:
    • Transmissible (conjugative) plasmids:
      • Can be transferred from cell to cell by conjugation
      • Contain transfer (tra) genes
      • Large in size
      • Usually present in a few copies per cell
      • Common in Gram negative bacteria
    • Non-transmissible (non-conjugative) plasmids:
      • Cannot be transferred from cell to cell
      • Do not contain transfer genes
      • Small in size
      • Frequently present in many copies per cell
      • Common in Gram positive bacteria

Bacterial Chromosome

  • Definition: Large, covalently closed, circular DNA molecule
  • Importance: Responsible for replication and protein synthesis
  • Chromosomal replication:
    • Definition: Process of cell multiplication
    • Steps:
      1. Entire two strands of chromosome separate
      2. Each strand is attached to a mesosome and acts as a template on which a complementary strand is formed by the action of DNA polymerase enzyme
    • New cell is formed, each cell will contain a copy of the chromosome
    • DNA replication occurs only in dividing cells

Extra-chromosomal Genetic Elements

Transposon

  • Definition: Extra-chromosomal elements that are generally different from chromosomes
  • Characteristics:
    • Much smaller than the chromosome
    • Carry only genes not essential for the life of bacteria
    • Can be transferred within and between bacteria species

Plasmid

  • Definition: Small, circular DNA molecules that can exist independently of the chromosome
  • Characteristics:
    1. Much smaller than the chromosome
    2. Carry only genes not essential for the life of bacteria
    3. Can be transferred within and between bacteria species

Gene Expression

  • Definition: Process of protein synthesis in which the sequence of nucleotides in a gene determines the sequence of amino acids in a protein
  • Steps:
    • Transcription:
      • Separation of the DNA strands of certain gene in the chromosome
      • One strand acts as a template to form a complementary strand (messenger RNA; mRNA) by the RNA polymerase enzyme
    • Translation:
      • The entire mRNA is translated into corresponding sequences of amino acids forming proteins on the surface of the ribosome

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Learn about the different types of bacterial variation, including phenotypic and genotypic variation, and their causes and characteristics.

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