module 24

Cell division is the biological process by which a single cell divides to produce two daughter cells.
- Successful division requires the parent cell to be adequately sized and contain sufficient nuclear and cytoplasmic components for both daughter cells.
- This process includes a growth phase and duplication of key components before division occurs.

Cells undergo different division processes depending on their classification as prokaryotic or eukaryotic.

Description: Prokaryotic cells, such as bacteria and archaea, reproduce via binary fission.
- Definition: Binary fission is the process by which one prokaryotic cell divides into two daughter cells.
- "Binary" refers to creating two daughter cells; "fission" means splitting in two.
Environmental Influence: Cell growth and division rates vary based on environmental conditions.
- Favorable conditions lead to rapid growth and division.
Binary Fission Steps (with reference to Escherichia coli):
1. Cell grows large enough to initiate division.
2. DNA replication occurs, producing two identical circular DNA molecules.
3. Each DNA molecule attaches to the inner membrane of the cell.
4. The attachment sites separate as the cell grows.
5. Once the cell is approximately double its original size, a constriction forms at the middle.
6. New membrane and wall synthesis completes the division, resulting in two identical daughter cells.
Speed: In some species, this cycle can occur in less than 20 minutes.
Asexual Reproduction: Binary fission is regarded as a form of asexual reproduction in prokaryotes, as offspring inherit DNA from a single parent.
Cell Division Insights: Prokaryotic division informs our understanding of mitochondrial and chloroplast division, both of which occur via binary fission, supporting the endosymbiont theory regarding eukaryotic origins.

Eukaryotic cells undergo a more complex type of cell division which consists of two main phases:
- M Phase (Mitotic Phase)
- The division of a parent cell into two daughter cells.
- Composed of two key events:
  1. Mitosis: Division of the nucleus.
  2. Cytokinesis: Division of the cytoplasm into two separate cells.
- Interphase: The phase between two M phases characterized by preparations for cell division.
Chromosomal Structure:
- Eukaryotic cells have multiple linear chromosomes, distinctly larger than the circular chromosomes of prokaryotes.
- Each chromosome must be accurately replicated and distributed during cell division, which requires nuclear envelope breakdown and reformation.

Describes the life cycle of a cell from its formation to the point where it divides again.
Composed of stages: M phase and Interphase.

G1 Phase: Prepares for DNA replication.
S Phase (Synthesis Phase):
- DNA molecules are duplicated, transforming each chromosome into two sister chromatids joined at a centromere.
- Example: Human cells with 23 pairs of chromosomes yield 46 sister chromatid pairs during this phase.
G2 Phase: Cell preparations for mitosis and cytokinesis; includes growth and protein synthesis.
G0 Phase: A non-dividing state where cells exit the cell cycle; can last from days to years, with some cells, such as nerve cells, never dividing again.

The process of dividing the cytoplasm into daughter cells, which occurs alongside mitosis.
In Animal Cells:
- Begins with the formation of a contractile ring, pinching the cell membrane to produce two cells.
In Plant Cells:
- Involves constructing a new cell wall using vesicles that fuse at the middle of the cell.

Cell division in prokaryotes (binary fission) is simpler and faster than in eukaryotes (mitosis and cytokinesis).
Both processes ensure the accurate distribution of genetic material to daughter cells, maintaining genetic continuity.