Cell Division: Prokaryotes and Eukaryotes

Cell Division in Prokaryotes: Binary Fission

• Binary fission is a type of asexual reproduction.
• Typically observed in prokaryotes and a few single-celled eukaryotes.

Binary Fission Detailed

• Prokaryotic cells (e.g., bacteria) reproduce through binary fission.
• Asexual reproduction where a parent cell divides to form two identical daughter cells.
• DNA replication occurs at a specific location, proceeds in two directions around the circular DNA molecule.
• Newly synthesized DNA attaches to the inner membrane.
• The cell elongates symmetrically.
• Membrane and wall material grow at the midpoint.
• This continues until the cell completely splits and the daughter cells become separate.
• Occasionally, mistakes in DNA replication can lead to daughter cells which are different.

Cell Division in Eukaryotes: Interphase, Mitosis, and Cytokinesis

• Process where a single cell becomes two identical daughter cells.
• In eukaryotes, mitosis is for growth and repair.

Cell Cycle (Eukaryotes)

• Cell division in eukaryotes proceeds through steps that form the cell cycle.
• Consists of two distinct stages:
  • Interphase: time between successive M phases.
  • Mitotic (M) phase: the time where the parent cell divides into two daughter cells.

Interphase

• Interphase is the phase of the cell cycle where most typical cells spend most of their life.
• The cell prepares for division during this stage.
• The cell increases in size.
• Sufficient amounts of cytoplasmic and membrane components are received by each daughter cell.
• DNA replication occurs in the nucleus.

Phases of the Cell Cycle

• G₁ phase
• S phase (Synthesis phase)
• G₂ phase
• G₀ phase (cell cycle arrest)

Mitosis Importance

• Essential process for life in multicellular organisms
• Prevents mutations
• Maintains organs

Mitosis Phases

• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis (Animal and Plant)

Prophase

• Chromosomes condense
• Centrosomes radiate microtubules and migrate to opposite poles.
• Nuclear membrane breaks down.

Prometaphase

• Microtubules of the mitotic spindle attach to chromosomes.
• Nuclear membrane starts to break down.

Metaphase

• Chromosomes align in the center of the cell.

Anaphase

• Sister chromatids separate and move to opposite poles of the cell.
• Centromeres split.

Telophase

• Chromosomes reach the poles of the cell.
• The nuclear envelope reforms, and chromosomes decondense.
• Cytoplasm divides, resulting in two daughter cells with identical genetic material.

Cytokinesis (Animal)

• A contractile ring forms to separate the two new cells.

Cytokinesis (Plant)

• A cell plate forms to separate the cytoplasm.

Meiotic Cell Division (Meiosis)

• Cell division in sexually reproducing organisms to produce gametes.
• Results in four genetically unique daughter cells.
• Each daughter cell contains half the number of chromosomes as the parent cell.
• Key importance: genetic diversity
•  Essential for reproduction from sexual organisms.

What Does Meiosis Do?

• Produces four daughter cells.
• Each daughter cell has half the number of chromosomes of the parent cell.
• Each daughter cell is genetically unique.

Meiosis Phases

• Meiosis I
• Meiosis II

Meiosis I

• Prophase I
• Metaphase I
• Anaphase I
• Telophase I

Meiosis II

• Prophase II
• Metaphase II
• Anaphase II
• Telophase II

Meiosis I: Prophase I

• Replicated chromosomes condense.
• Synapsis begins.
• Bivalent forms and crossing over occurs.
• Synaptonemal complex dissociates.

Meiosis II

• The nuclear envelope breaks down and chromosomes condense.
• Chromosomes align in the center of the cell.
• Sister chromatids separate.
• The nuclear envelope reforms.
• Cytokinesis occurs.
•  Four haploid daughter cells are formed; each one having only one chromosome of each homologous pair.

Abnormal Cell Division (Diseases)

• Cancer
• Chromosome abnormalities
• Developmental disorders
• Neurodegenerative diseases

Explore the mechanisms of cell division, focusing on binary fission in prokaryotes and mitosis in eukaryotes. Learn how these processes contribute to asexual reproduction and cellular growth. Test your understanding of the different stages involved in cell division.