Overview of Apoptosis and Its Functions

Questions and Answers

What is the definition of apoptosis?

Apoptosis is programmed (genetically regulated) cell death that eliminates cells that are no longer needed or dangerous cells.

What is the function of apoptosis?

To sculpt body structures, eliminate unnecessary tissues, maintain balance between cell division and cell death, and roles in aging and diseases.

What is the difference between apoptosis and necrosis?

Apoptosis is programmed cell death that occurs neatly; necrosis is death by injury leading to inflammation and damage to neighboring cells.

Which change happens in the plasma membrane of an apoptotic cell?

Phosphatidylserine is moved from the inner to the outer leaflet of the plasma membrane. Signup and view all the answers

What happens to cytochrome c in an apoptotic cell?

Cytochrome c relocates from the intermembrane space of the mitochondria to the cytosol. Signup and view all the answers

Which techniques are used to detect apoptosis?

DNA laddering and TUNEL staining. Signup and view all the answers

What is a caspase?

Caspases are cysteine-dependent aspartate-directed proteases that mediate apoptosis. Signup and view all the answers

Describe the extrinsic pathway to caspase activation.

Cell-surface Fas receptor activation triggers apoptosis when a killer lymphocyte binds to the Fas receptor. Signup and view all the answers

Describe the intrinsic pathway to caspase activation.

Apoptotic stimulus releases cytochrome c from mitochondria, activating adaptor proteins and forming an apoptosome. Signup and view all the answers

What are the 3 different classes of Bcl2 regulators?

Anti-apoptotic, pro-apoptotic, and BH3-only. Signup and view all the answers

What can be defined as pro-apoptotic stimuli?

Increased levels of oxidants, DNA damage, chemotherapeutic drugs, improperly folded proteins, death activators, and withdrawal of positive signals. Signup and view all the answers

What is the function of survival factors?

Survival factors suppress apoptosis by regulating Bcl2-family proteins. Signup and view all the answers

What is the function of mitogens?

Mitogens stimulate cell division by inhibiting the retinoblastoma protein via CDKs. Signup and view all the answers

What is the function of growth factors?

Growth factors stimulate cell growth and increase in size and mass. Signup and view all the answers

What may happen if cells fail to undergo apoptosis?

Failure of apoptosis may lead to cancer. Signup and view all the answers

What happens if an oncogene is lost or if it's overactive?

If lost, there is less growth; if overactive, it drives extra growth, possibly leading to cancer. Signup and view all the answers

Study Notes

Apoptosis Overview

Apoptosis is programmed cell death that selectively eliminates unneeded or harmful cells.

Functions of Apoptosis

Crucial for sculpting body structures, such as neural wiring and limb development.
Eliminates unnecessary tissues, e.g., a tadpole’s tail.
Maintains tissue homeostasis by balancing cell division and death.
Plays a role in aging and various diseases.

Comparison: Apoptosis vs. Necrosis

Apoptosis is a controlled, physiological process of cell death, where cells shrink and are cleared without harming others.
Necrosis involves pathological cell death, where cells swell and rupture, causing inflammation and damage to surrounding cells.

Plasma Membrane Changes

During apoptosis, phosphatidylserine shifts from the inner to the outer plasma membrane leaflet, signaling phagocytes to clear the cell.

Cytochrome c in Apoptosis

Cytochrome c is released from mitochondria to the cytosol during apoptosis, an important step in the apoptotic process.

Detection Techniques for Apoptosis

DNA laddering: visualizes DNA fragmentation indicating cell death.
TUNEL staining: labels fragmented DNA with fluorescent markers.
Detection of cytochrome c in the cytosol signifies apoptotic activity.

Caspases

Caspases are cysteine-dependent proteases central to apoptosis.
Initiate and amplify the apoptotic process through a caspase cascade.

Extrinsic Pathway of Caspase Activation

Triggered by Fas receptor activation on the cell's surface.
Interaction with lymphocyte fas ligand initiates the caspase signaling cascade.

Intrinsic Pathway of Caspase Activation

Involves the release of cytochrome c from mitochondria.
Cytochrome c forms an apoptosome with adaptor proteins, activating procaspase-9 leading to apoptosis.

Bcl2 Family of Regulators

Consists of anti-apoptotic (Bcl-2), pro-apoptotic (Bax, Bak, Bad), and BH3-only proteins.
The balance of these proteins decides cell survival or death.

Pro-apoptotic Stimuli

Increased oxidative stress.
DNA damage from UV or X-ray exposure.
Chemotherapeutic drug effects.
Accumulation of misfolded proteins.
Exposure to death activators like Fas.
Withdrawal of growth and survival signals.

Role of Survival Factors

Suppress apoptosis by modulating Bcl2-family proteins, promoting cell survival.

Function of Mitogens

Stimulate cell division by inhibiting the activity of the retinoblastoma protein via cyclin-dependent kinases (CDKs).

Function of Growth Factors

Promote cell growth by increasing cell size and mass.

Consequences of Failed Apoptosis

Can lead to uncontrolled cell growth and the development of cancer.

Oncogenes

Oncogenes normally promote cellular growth and survival.
Loss of an oncogene reduces growth; overactivity may push towards cancerous growth.

Tumor Suppressor Genes

Typically inhibit excessive cell growth.
Loss of function can lead to unregulated cell proliferation, potentially resulting in cancer.

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Description

Explore the fundamental concepts of apoptosis, the process of programmed cell death. This quiz covers the functions and importance of apoptosis in development, tissue homeostasis, and comparison with necrosis. Understand key molecular changes and their implications in health and disease.