Cell Biology: Apoptosis and Development

Programmed Cell Death (Apoptosis)

• Apoptosis is an active process of cellular changes leading to cell death.
• It's a normal, controlled part of organism growth and development.
• The body uses apoptosis to eliminate unwanted or abnormal cells.
• The term "apoptosis" is derived from the Greek word for the falling of leaves from a tree or petals from a flower.
• It distinguishes this programmed cell death from accidental cell death caused by injury or inflammation.

Animal Development and Cell Balance

• Animals start as a single cell (fertilized egg) and, undergoing rapid proliferation, differentiate into a vast array of specialized cells.
• Humans have an estimated 10¹⁴ cells with over 200 distinct types.
• In multicellular organisms, cell death and proliferation are balanced throughout life.
• The complex process of development also involves maintaining a balance between cell death and proliferation.

Types of Cell Death: Apoptosis vs Necrosis

• Apoptosis is a programmed cellular suicide occurring in a normal or regulated manner.
• Necrosis, typically a result of severe cellular injury, leads to the death of groups of cells and often causes inflammation.

Apoptosis Stages and Characteristics

• Apoptosis involves a series of distinct cellular changes.
• Apoptotic cells shrink and form membrane blebs, with the nucleus breaking into fragments
• Apoptosis also involves the formation of apoptotic bodies, which are then phagocytosed by neighboring cells or macrophages.
• Neighboring cells remain healthy during apoptosis.
• Apoptotic cell death doesn't cause an inflammatory response.

Importance of Apoptosis

• Apoptosis is essential for balancing cell numbers in tissues undergoing turnover.
• Apoptosis serves as a defense mechanism to eliminate potentially damaged or dangerous cells.
• Apoptosis plays a crucial role during embryonic development, maintaining homeostasis in adults, and aiding in responses to disease states, and fighting infections.
• Cells infected by viruses often undergo programmed cell death to limit viral production and spread.

Cellular Renewal in Adults

• Cellular renewal, balancing cell death with cell replacement by stem cells, is essential in mature (adult) organisms and tissues.
• The capacity of stem cells to differentiate into various cell types is critical for tissue repair and regeneration.

Types of Molecules Involved

• Phosphatidylserine: A cell membrane component that signals apoptotic cells for removal.
• Growth factors: Essential for cell survival in many tissues
• Extracellular matrix: Plays a role in regulating cell-cell interactions and cell survival.

Intrinsic and Extrinsic Pathways

• Two pathways lead to apoptosis.
• The intrinsic pathway includes internal surveillance mechanisms or signals affecting cell pathways or DNA damage.
• The extrinsic pathway is initiated by signals from other cells and involves the interaction of "killers" with specific receptors.
• These pathways often interplay.

Common Causes of Apoptosis

• Developmentally defective cells.
• Excess cells
• Cells with perturbed cell cycles
• Virus-infected cells
• Chemotherapeutic treatments

The Bcl-2 Family

• The Bcl-2 family of proteins regulates apoptosis, with anti-apoptotic and pro-apoptotic proteins.
• Factors such as nutrient withdrawal and/or environmental changes that signal apoptosis

Explore the crucial processes of programmed cell death (apoptosis) and animal development. Understand how these processes maintain cellular balance in multicellular organisms. This quiz covers the definitions, differences, and significance of apoptosis and necrosis.