micro unit 2 day 2

Endospores and Bacterial Survival

• Endospores:

  • Survival structure, not a reproductive structure.

  • Only a few bacterial cells can produce endospores; most rely on replication for survival.

Cell Replication

• Binary Fission:

  • Process where cells replicate, meaning 'to cut in two.'

  • More complex than just cutting because cellular components must be properly organized and replicated.

Mechanism of Binary Fission

1. **Cell Growth:

   • Cell enlarges before division, maintaining adequate size and volume to support cellular functions.

• Replicating cells must avoid getting smaller with each division; they must reach a minimum size.

2. Asexual Reproduction:

   • Bacterial cell division is asexual; offspring are clones of the parent cell, no blending of traits.

   • It is termed amitotic since it lacks the processes involved in mitosis, like prophase, metaphase, and cytokinesis.

3. Role of Chromosomes:

   • Chromosomes are not pulled apart but pushed apart as the cell grows and divides.

   • Unique to bacteria and archaea.

4. Cell Membrane Pinching:

   • The septum begins to form as the cell membrane pinches inward at the cell's midpoint, directed by proteins (e.g., FTSZ).

DNA and Genetic Replication

• DNA Replication:

  • Attached DNA: DNA attaches to the cell membrane during replication.

  • Semi-Conservative Process:

    • Each new DNA molecule consists of one original strand and one newly synthesized strand, minimizing errors during replication.

    • Ensures that the original genetic information is maintained.

Bacterial Genome

• Characteristics:

  • Approx. 3,200 genes in a typical bacterial genome.

  • The replication process occurs at the cell membrane, enabling simultaneous transcription and translation.

  • Bacterial DNA is circular and does not have a defined nucleus, making replication distinct from eukaryotic DNA replication.

Speeding Up Replication

1. Multiple Points of Origin:

   • Bacteria can initiate DNA replication at several points to speed up the process.

   • More points of origin result in shorter replication times (e.g., two origins halves the time).

2. Theta Structure:

   • During replication, bacteria inherit a theta structure (an intact genome under replication), ensuring efficiency as a portion of the genome can be replicated prior to fission.

Cell Division and Arrangement

• Planes of Division:

  • Determines how cells divide and whether they remain attached or separate post-division.

  • Examples:

    • Bacilli divide and might remain in pairs or chains.

    • Staphylococci cluster due to multiple planes of division.

  • The genetics of the cell determines its division characteristics (e.g., how many planes of division).

Summary of Bacterial Cell Division

• Overall, bacterial cells replicate through binary fission, which involves:

  1. Cell enlargement and DNA attachment to the membrane.

  2. Replication of DNA and all cellular components.

  3. Formation of a septum and building of cell walls.

  4. Completion of the division process resulting in two genetically identical daughter cells.