Cell Death For,s

Question 1

What are the three main forms of cell death?

Answer 1

Necrosis: Traumatic cell death due to acute injury (e.g., hypoxia).

2. Apoptosis: Programmed cell death (e.g., DNA damage, cytotoxic T-cell contact).
3. Excitotoxicity: Neural tissue-specific cell death caused by disturbed glutamate homeostasis.

Question 2

What are the characteristics of necrosis?

Answer 2

Membrane damage.

• Chromatin flocculation.

• Rapid depletion of energy levels.

• Leakage of cell contents causing inflammation.

Question 3

What are the characteristics of apoptosis?

Answer 3

Intact membrane with blebbing (membrane protrusions).

• Chromatin condensation and nuclear shape distortion.

• Energy levels maintained or slowly depleted.

• No inflammation (engulfed by phagocytes before spilling contents).

Question 4

What are the steps in apoptosis?

Answer 4

Chromatin condensation and membrane blebbing.

2. Cell fragmentation into apoptotic bodies.
3. Apoptotic bodies attract phagocytes via externalized phosphatidylserine.
4. Phagocytes bind to receptors, stimulate anti-inflammatory cytokines, and engulf the dying cell.

Question 5

What are common triggers for apoptosis?

Answer 5

DNA damage.

• Viral infection.

• Cancer cells.

• Developmental processes (e.g., metamorphosis).

• Self-tolerance (elimination of autoimmune lymphocytes).

Question 6

What are biochemical markers of apoptosis?

Answer 6

DNA fragmentation creates a ladder pattern in gel electrophoresis.

• TUNEL assay detects free DNA ends by labeling with dUTPs.

• Phosphatidylserine externalization detected by Annexin V protein.

• Loss of mitochondrial electrochemical gradient measured with fluorescent dyes.

Question 7

What enzymes drive apoptosis?

Answer 7

• Caspases: Proteases with cysteine active sites that cleave substrates at aspartate residues.

• Caspases are tightly regulated to prevent premature activation.

Question 8

What are the two apoptotic pathways?

Answer 8

1. Extrinsic Pathway:

• Triggered by extracellular signals.

• Death receptors bind ligands and activate caspases.

2. Intrinsic Pathway:

• Stimuli cause mitochondrial membrane leakage.

• Cytochrome C release activates caspases

Question 9

What role does UV radiation play in apoptosis?

Answer 9

UV-B (sunlight): Causes thymine dimers in DNA, leading to replication errors, mutations, and apoptosis (helps limit skin cancer).

• UV-C: Lethal, but absorbed by the ozone layer.

Question 10

How does insufficient or excessive apoptosis cause disease?

Answer 10

Insufficient Apoptosis: Autoimmune diseases (failure to eliminate lymphocytes).

• Excessive Apoptosis: Diseases like type 1 diabetes mellitus.

Question 11

What is excitotoxicity?

Answer 11

: A form of neural cell death caused by excessive glutamate, leading to prolonged receptor activation and intracellular calcium buildup.

Question 12

Q12: How does glutamate homeostasis work?

Answer 12

Glutamate is synthesized from glutamine in the Krebs cycle.

• Released into the synaptic cleft for nerve impulses.

• Recycled back into cells via vesicular pumps.

Question 13

Q13: What happens during disturbed glutamate homeostasis?

Answer 13

Excess glutamate is released (e.g., during hypoxia).

• Prolonged activation of NMDA and AMPA receptors leads to calcium entry.

• Ca2+-dependent enzymes degrade phospholipids and other biomolecules, causing cell death.

Question 14

What clinical conditions are associated with excitotoxicity?

Answer 14

Stroke.

• Trauma.

• Neurodegenerative diseases.