Meiosis, Further Cell Theory

Meiosis and further cell theory explained in one loooong flashcard.

Apoptosis

Programmed cell death, a controlled process that removes damaged, unnecessary, or harmful cells without causing inflammation.

Overview of Apoptosis

Trigger: G2 phase cell unable to repair DNA → Apoptosis signal received (internal/external) → Caspase cascade activated

Process:

1. Caspases cleave DNA, nuclear proteins, plasma membrane

2. Structural breakdown – Membrane, cytoskeleton degrade → Cell shrinks & blebs → Apoptotic bodies form

3. Removal: Macrophages signal → Apoptotic bodies removed via endocytosis

Caspases

Enzymes activated in apoptosis (intrinsic/extrinsic). They:

• Chop DNA into fragments

• Break down nuclear, cytoplasmic, and membrane proteins

• Dismantle the cytoskeleton

• Shrink the cell and form blebs

Active Caspases Pathway

🔹 Intrinsic (mitochondrial): Triggered by internal damage (e.g., radiation, DNA damage, infection). Releases apoptosis factors→ activates caspases→ controlled cell breakdown.
🔹 Extrinsic (Death Receptor): Triggered by external signals (e.g., cytokines, cytotoxic drugs, immune cells, hormones, pathogens). Death receptor activation → caspases → cell disassembly.

Stem cells

Unspecialized cells with the ability to divide and differentiate into specialized cell types.

Stages of Stem Cells (Embryonic Development)

• Zygote (A): Single-cell stage after fertilization.

• 2-cell stage (B): Initial division.

• Morula (C): Solid ball of cells.

• Blastula/Blastocyst (E): Hollow ball of cells where embryonic stem cells are collected.

• Gastrula (F): Stage where differentiation begins.

Type of stem cell potency

• Totipotent:

  • Source: Zygote or early-stage embryo.

  • Potential: Can form all cell types, including embryonic and extra-embryonic tissues (e.g., placenta).

• Pluripotent:

  • Source: Inner cell mass of the blastocyst.

  • Potential: Can form all body cells but not extra-embryonic tissues.

• Multipotent:

  • Source: Adult stem cells (e.g., bone marrow, brain).

  • Potential: Can form related cell types within a specific tissue or organ system.

Other Types of Stem Cells: Embryonic, Adult, Potency

• Embryonic Stem Cells:

  • Collected at the blastocyst stage (Image E).

  • These cells are pluripotent, meaning they can develop into nearly any cell type.

• Other Types of Stem Cells:

  • Adult Stem Cells: Found in tissues like bone marrow; typically multipotent, meaning they can develop into related cell types (e.g., blood cells from hematopoietic stem cells).

• Stem Cell Potency:

  • Potency: The ability of stem cells to differentiate into different cell types.