Retta - L17

Apoptosis Overview

• Apoptosis is a physiological process that regulates animal cell numbers through controlled cell death.
• Two main pathways of apoptosis: intrinsic and extrinsic, which are influenced by extracellular factors.

Mechanisms of Cell Growth and Division

• Cell proliferation equals cell division, influenced by extracellular growth factors that also promote cell growth.
• Different organisms may separate triggers for cell growth and division; some require both growth factors and nutrients.
• Protein kinases, such as mTOR, stimulate protein synthesis while inhibiting degradation.

Balance Between Cell Proliferation and Cell Death

• Coordination of cell proliferation and apoptosis is crucial for regulating tissue growth.
• Bax promotes apoptosis, while Bcl-2 supports cell survival; an equilibrium between these factors is essential for normal physiological processes.

DNA Damage and Apoptosis

• DNA damage can trigger apoptosis if repair mechanisms fail; this serves as protection against pathological conditions like cancer.
• Activation of the ATM/ATR kinase system phosphorylates p53, which promotes cell cycle arrest or induces apoptosis.

Caspases and Apoptosis

• Apoptosis is mediated by caspases, proteolytic enzymes that cleave specific proteins to induce cell death.
• Initiator caspases (e.g., caspases 8 and 9) activate effector caspases (e.g., caspases 3 and 7) to trigger the apoptotic cascade.

Extrinsic and Intrinsic Pathways

• The extrinsic pathway is initiated by cell surface death receptors (e.g., TNF-alpha, Fas, TRAIL).
• The intrinsic pathway involves mitochondrial signaling, with caspases activated regardless of the pathway.

Morphological Features of Apoptosis

• Characteristic features of apoptotic cells include chromatin condensation, nuclear fragmentation, and formation of apoptotic bodies.
• Apoptotic bodies are essentially vacuoles containing cytoplasm and intact organelles, which are eventually cleared by phagocytes.

Distinctions Between Apoptosis and Necrosis

• Apoptosis is a controlled process that avoids inflammation, while necrosis is accidental cell death that can damage surrounding tissues; necrotic cells release inflammatory signals.
• Key differences: apoptosis features chromatin condensation and organized cell death, while necrosis involves cell rupture and inflammation.

Alternate Cell Death Mechanisms

• Necroptosis is a form of programmed necrosis, often triggered in response to viral infections when caspase pathways are inhibited.
• Autophagy refers to the process of self-eating, wherein damaged organelles are degraded to prevent toxicity; it is more of a survival mechanism than a cell death process.

Role of Autophagy

• Autophagy involves formation of phagophores that encapsulate damaged organelles, fusing with lysosomes to degrade materials into reusable components.
• Proper autophagy is essential for cellular health; dysfunction can lead to various diseases.### Autophagy Overview
• Autophagy is a catabolic process essential for maintaining intracellular energy balance.
• It eliminates harmful proteins and damaged organelles, such as dysfunctional mitochondria.
• Functional macromolecules are recycled into cells, contributing to amino acid availability for cellular functions.

Types of Autophagy

• Macroautophagy: Classical form of autophagy that engulfs large cellular components.
• Chaperone-Mediated Autophagy (CMA): Targets altered proteins for degradation by delivering them to lysosomes.
• Microautophagy: Involves direct engulfment of cellular cargo by lysosomes for degradation.

Mitophagy

• Mitophagy is a specialized autophagic process focused on degrading abnormal mitochondria.
• Degradation of dysfunctional mitochondria plays a crucial role in various pathophysiological conditions.

Nobel Prize in Autophagy

• Yoshinori Ohsumi received the Nobel Prize in 2016 for elucidating the mechanisms of autophagy, significantly advancing understanding of cellular degradation processes.

This quiz focuses on the critical topic of apoptosis, exploring both the intrinsic and extrinsic pathways involved in cell death. We will discuss the regulatory mechanisms and physiological roles of apoptosis in maintaining proper cell numbers in animal organisms. Prepare to test your understanding of these vital cellular processes.