Cell Division: Mitosis and Meiosis

Definition: A type of cell division that reduces the chromosome number by half, resulting in four genetically diverse gametes.
Stages:
- Meiosis I:
  - Prophase I: Homologous chromosomes pair (synapsis) and exchange genetic material (crossing over).
  - Metaphase I: Homologous pairs align at the cell equator.
  - Anaphase I: Homologous chromosomes separate and move to opposite poles.
  - Telophase I: Two haploid cells form, each with half the number of chromosomes.
- Meiosis II: Similar to mitosis but involves the division of sister chromatids, resulting in four haploid daughter cells.
Significance: Ensures genetic diversity through recombination and independent assortment.

Definition: A process of cell division that results in two genetically identical diploid daughter cells.
Stages:
- Prophase: Chromatin condenses into chromosomes; nuclear envelope disintegrates.
- Metaphase: Chromosomes align along the metaphase plate.
- Anaphase: Sister chromatids separate and move toward opposite poles.
- Telophase: Nuclear envelope re-forms; chromosomes de-condense.
- Cytokinesis: Cytoplasm divides, resulting in two separate cells.
Significance: Essential for growth, development, and tissue repair.

Phases:
- Interphase:
  - G1 (Gap 1): Cell growth and organelle duplication.
  - S (Synthesis): DNA replication.
  - G2 (Gap 2): Preparation for mitosis; checks for DNA damage.
- M Phase: Mitosis and cytokinesis.
Duration: Varies by cell type; somatic cells typically take about 24 hours.
Checkpoints:
- G1 checkpoint (to assess size and DNA integrity).
- G2 checkpoint (to assess DNA replication).
- M checkpoint (to ensure chromosomes are properly aligned).

Definition: Programmed cell death, a vital process for maintaining tissue homeostasis.
Signaling Pathways:
- Intrinsic (mitochondrial) pathway: Triggered by internal stress signals.
- Extrinsic (death receptor) pathway: Triggered by external signals binding to death receptors on the cell surface.
Key Phases:
- Cell shrinkage, chromatin condensation, and fragmentation of the nucleus.
- Formation of apoptotic bodies that are phagocytosed by neighboring cells.
Importance: Eliminates damaged or unnecessary cells without causing an inflammatory response.

Key Regulators:
- Cyclins and Cyclin-dependent Kinases (CDKs): Govern progression through the cell cycle.
- Growth factors: Stimulate cell division, particularly in response to external signals.
Inhibitory Mechanisms:
- Tumor suppressor genes (e.g., p53) can halt the cell cycle in response to DNA damage.
- Contact inhibition: Cells stop dividing when they come in contact with neighboring cells.

Definition: Abnormal growths of tissue that can be benign (non-cancerous) or malignant (cancerous).
Characteristics of Cancer Cells:
- Uncontrolled cell division.
- Ability to invade other tissues (metastasis).
- Evasion of apoptosis and increased longevity.
Genetic Factors: Mutations in oncogenes (promote cell division) and tumor suppressor genes (inhibit division) are key drivers of tumorigenesis.
Therapeutic Approaches:
- Surgery, radiation therapy, chemotherapy, and targeted therapies to eliminate cancerous cells or inhibit their growth.

Reduces chromosome number by half during gamete formation
Genetic diversity through recombination (crossing over) and independent assortment
Prophase I: Homologous chromosomes pair (synapsis) and exchange genetic material
Metaphase I: Pairs align on the cell equator
Anaphase I: Homologous chromosomes separate
Telophase I: Two haploid cells with half the number of chromosomes form
Meiosis II: Similar to mitosis, dividing sister chromatids resulting in four haploid daughter cells

Ordered series of events leading to cell division
Phases:
- Interphase: G1 (growth), S (DNA replication), G2 (preparation)
- M Phase: Mitosis and cytokinesis
Duration: Varies by cell type but typically takes about 24 hours for somatic cells
Checkpoints:
- G1: Assesses cell size, DNA integrity
- G2: Assesses DNA replication
- M: Ensures chromosomes are properly aligned

Programmed cell death that maintains tissue homeostasis
Signaling Pathways:
- Intrinsic: Internal stress signals
- Extrinsic: External signals binding to death receptors
Key Phases:
- Cell shrinkage, chromatin condensation, nuclear fragmentation
- Formation of apoptotic bodies phagocytosed by neighboring cells
Importance: Eliminates damaged cells without causing an inflammatory response

Key Regulators:
- Cyclins and Cyclin-dependent Kinases (CDKs): Govern cell cycle progression
- Growth factors: Stimulate cell division in response to signals
Inhibitory Mechanisms:
- Tumor suppressor genes (e.g., p53): Halt the cell cycle in response to DNA damage
- Contact inhibition: Cells stop dividing when they contact neighboring cells

Abnormal growths of tissue
Benign (non-cancerous) or malignant (cancerous)
Characteristics of Cancer Cells:
- Uncontrolled cell division
- Ability to invade other tissues (metastasis)
- Evasion of apoptosis and increased longevity
Genetic Factors: Mutations in oncogenes and tumor suppressor genes are key drivers of tumorigenesis
Therapeutic Approaches:
- Surgery, radiation therapy, chemotherapy, targeted therapies to eliminate or inhibit growth