Biology Chapter 23: Cell Death

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Questions and Answers

What is the main difference between necrosis and apoptosis?

Necrosis is a pathological process, while apoptosis is a physiological process. (correct)

Necrosis is a physiological process, while apoptosis is a pathological process.

Apoptosis is a passive process, while necrosis is an active process.

What happens to the plasma membrane during apoptosis?

It disappears, releasing mitochondria.

It remains intact, but portions bud off. (correct)

It ruptures, releasing intracellular contents.

It increases in volume and then bursts.

What is the result of disturbances in apoptosis pathways?

Cancer, autoimmune diseases, and neurodegenerative disorders. (correct)

Cell division and differentiation.

Programmed cell death and tissue physiology.

Inflammatory responses and tissue damage.

What is the purpose of apoptosis in cellular physiology?

To remove damaged cells and maintain tissue homeostasis. Signup and view all the answers

What happens to the mitochondria during apoptosis?

They release cytochrome c, but remain within blebs. Signup and view all the answers

What is the result of necrosis?

Groups of cells die simultaneously, inducing an inflammatory response. Signup and view all the answers

What is the function of scramblase during apoptosis?

To flip phosphatidylserine to the outer membrane surface, serving as an 'eat-me' signal. Signup and view all the answers

What happens to chromatin during apoptosis?

It condenses and segments. Signup and view all the answers

What is the role of active caspase 9 in apoptosis?

To initiate the caspase proteolytic cascade Signup and view all the answers

What type of proteins are caspases?

Cysteine proteases Signup and view all the answers

What is the function of the death domain (DD) in TNFR?

To transmit the apoptotic signal Signup and view all the answers

What is the role of Fas death receptor in apoptosis?

To initiate apoptotic cell death when engaged by Fas ligand Signup and view all the answers

What is the function of caspases in apoptosis?

To degrade cellular components in the apoptotic cell Signup and view all the answers

What is the significance of the post-translational modification of caspases?

To ensure rapid activation of caspases when needed Signup and view all the answers

What is the role of T-cytotoxic cells in apoptosis?

To express Fas ligand to stimulate the apoptotic death of host cells Signup and view all the answers

What is the difference between Fas and TNFR1 in death signaling?

Fas is more potent in death signaling than TNFR1 Signup and view all the answers

What is the primary function of phosphatidylserine in the process of apoptosis?

Marking apoptotic cells for recognition by phagocytic cells Signup and view all the answers

What is the role of p53 protein in the process of apoptosis?

Halting the cell cycle and stimulating apoptosis Signup and view all the answers

During development, what is the primary function of apoptosis?

Removing excess cells to allow for normal development and function Signup and view all the answers

What is the result of incomplete apoptosis during development?

Abnormal structures Signup and view all the answers

What is the primary function of apoptosis in maintaining tissue homeostasis?

Maintaining a balance between cell division and death Signup and view all the answers

What is the primary function of the Apoptosome?

Triggering the formation of apoptotic protease activating factor Signup and view all the answers

What is the role of Bax in the initiation of apoptosis?

Inserting into the mitochondrial membrane, allowing cytochrome c to exit Signup and view all the answers

What is the result of apoptosis in the vertebrate nervous system?

More than half of the nerve cells undergo programmed cell death Signup and view all the answers

Study Notes

Cell Death

Cells die through either necrosis or apoptosis.

Necrosis

Passive, pathological process that occurs due to cellular injury or accidental means
Affects groups of cells simultaneously, causing cell membranes to rupture and release intracellular contents into surrounding tissue fluids
Often induces an inflammatory response
Completes within several days

Apoptosis

Active, normal, physiological process that removes individual cells without damaging neighboring cells or inducing inflammation
Ensures cells live only when and where needed
Characteristics:
- Cell shrinkage, but no lysis
- Plasma membrane remains intact, but portions bud off (blebbing)
- Phosphatidylserine in the inner membrane flips to the cell surface, serving as an "eat-me" signal to phagocytic cells
- Mitochondria releases cytochrome c in an ATP-dependent process, but remains within blebs
- Chromatin segments and condenses
- Apoptotic bodies are formed and engulfed by phagocytic cells, recognized by the presence of phosphatidylserine
- Completed within a few hours

Biological Significance of Apoptosis

Removes damaged cells, infected cells, or starved cells, saving nutrition and preventing viral spread
Essential during development to remove excess cells and sculpt developing tissues
Maintains tissue homeostasis by balancing cell division and death to maintain a constant cell number

Initiation of Apoptosis

Apoptosome (Internal Cell Death Program)
- Initiated by irreparable damage to cellular components or DNA
- Bax (proapoptotic protein, Bcl-2 family) is inserted into the mitochondrial membrane, allowing cytochrome c to exit into the cytoplasm
- Cytochrome c in the cytosol triggers the formation of Apoptosome using ATP
- Cytoplasmic cytochrome c activates Apaf-1, which activates caspase 9, initiating the caspase proteolytic cascade
Death receptor (External Cell Death Program)
- Triggered by death receptors (e.g., Fas, TNFR)
- Recognizes specific ligands, and the tumor necrosis factor receptor (TNFR) possesses a homologous cytoplasmic sequence termed the "death domain (DD)"
- Adaptor molecules such as FADD and TRADD contain DDs, interacting with death receptors to transmit the apoptotic signal

Caspase Family of Proteases

Caspases are proteases that are major effectors of apoptotic cell death
Members of the cysteine protease class
Synthesized as inactive zymogen or proenzyme forms and are activated to become functional proteases when needed

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Description

Learn about the two types of cell death, necrosis and apoptosis, and their differences in terms of cellular injury, inflammation, and physiological process.