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Overview of Programmed Cell Death (Apoptosis)

• Previous topic: Mitochondria and chloroplasts

• Key theme: Programmed cell death (apoptosis)

Introduction to Apoptosis

• Definition:
    - Apoptosis is a controlled cellular process in which a cell intentionally destroys itself.

• Purpose of apoptosis:
    - Occurs in response to:
      - Damaged molecules (e.g., DNA damage beyond repair)
      - Viral infections
      - Removal of unneeded cells during development (e.g., interdigital cell death)

Differences Between Apoptosis and Necrosis

• Apoptosis:
    - Organized, controlled, orderly process
    - Prevents harm to surrounding tissues
    - Normal part of organism growth and development

• Necrosis:
    - Accidental cell death
    - Uncontrolled process
  

Examples of Apoptosis

• Interdigital cell death in development:
    - Removal of soft tissue between fingers, allowing normal digit formation
    - Example in chickens: Removal of tissue between toes facilitates adapted foot morphology (e.g., webbed feet) through apoptosis

Characteristics of Apoptotic Cells

• Distinct features:
    - Cellular shrinkage
    - Protrusion of the plasma membrane (blebbing)
    - Fragmentation of DNA
      - DNA is broken into smaller pieces
    - Loss of attachment to surrounding cells
    - Engulfment by phagocytes
  

Mechanism of Apoptosis

Intrinsic Pathway

• Internally triggered by stimuli, such as:
    - Genetic damage
    - Hypoxia (reduced oxygen levels)
    - Viral infections

• Role of mitochondrial membrane:
    - Change in mitochondrial membrane potential
    - Release of cytochrome c from mitochondria into the cytosol

Caspases in Apoptosis

• Caspases: Enzymes that are key to the apoptosis process
    - Caspase 9 (initiator)
    - Caspase 3 (executioner)

• Measurements of caspase levels and cytochrome c can indicate cell health:
    - Increased levels signifying apoptosis

Comparison of Normal and Apoptotic Cells

Apoptosis and Disease

• Too little apoptosis:
    - Leads to cancer
    - Malignant cells persist and proliferate

• Too much apoptosis:
    - Linked to degenerative diseases (e.g., Alzheimer's, Parkinson's)
    - Excessive cell death can lead to cellular aggregation and signal disruption

Summary of Apoptosis and Mitochondria

• Key components:
    - Release of cytochrome c from mitochondria as a signal for apoptosis
    - Importance of cytochrome c concentration monitoring

Cell Tissue and Organelles

• Distinction between cytosol and cytoplasm:
    - Cytosol: Liquid component
    - Cytoplasm: Includes organelles and cytosol

• Endoplasmic Reticulum (ER):
    - Rough ER: Protein synthesis
    - Smooth ER: Lipid synthesis

• Golgi Apparatus:
    - Modifies, packages, and sorts proteins

• Lysosomes:
    - Involved in degradation and recycling

Endomembrane System

• Composed of interconnected membranes facilitating protein transport within the cell

• Involves processes:
    - Nuclear envelope
    - Endoplasmic Reticulum and Golgi interactions
    - Exocytosis and endocytosis mechanisms

Proteins and Vesicle Trafficking

• Use of fluorescent proteins (e.g., GFP) for tracking proteins in live cells

• Importance of motor proteins (e.g., kinesin) for vesicle movement on cytoskeleton
    - Actin microfilaments in plant cells
    - Microtubules in animal cells

Summary of Vesicle Dynamics

• Vesicles bud off from donor compartments (e.g., ER, Golgi)

• Process of docking and fusion with target membranes:
    - Involves SNARE proteins
    - Tethering proteins (e.g., Rab proteins) assist in anchoring vesicles

Conclusion

• Understanding apoptosis is crucial for insights into developmental biology, cancer, and degenerative diseases

• The endomembrane system is essential for intracellular communication and protein distribution

• Ongoing research focuses on these mechanisms for therapeutic applications.