Apoptosis and Its Pathways

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Questions and Answers

What function do initiator caspases serve in the apoptotic process?

They cleave substrates to dismantle the cell.

They maintain cell membrane integrity.

They activate executioner caspases. (correct)

They scavenge dead and damaged cells.

What is the role of phagocytic cells in relation to apoptosis?

They initiate the apoptotic process.

They remove fragments of cells undergoing apoptosis. (correct)

They delay the apoptosis process.

They regenerate damaged cells.

Which protein family is essential for the execution of apoptosis by cleaving proteins?

Cytokines

Caspases (correct)

Bcl2 proteins

Proteasomes

Which type of apoptosis is triggered by external signals binding to death receptors?

Extrinsic pathway Signup and view all the answers

What is a key function of Bcl2 proteins in apoptosis?

They inhibit the activity of executioner caspases. Signup and view all the answers

What is the role of adaptor proteins in the activation of caspases during apoptosis?

They facilitate procaspase dimerization. Signup and view all the answers

What type of caspase is responsible for cleaving executioner procaspases?

Initiator caspases Signup and view all the answers

Which of the following proteins is involved in DNA fragmentation during apoptosis?

CAD Signup and view all the answers

Which statement about executioner caspases is true?

They exist as inactive dimers before activation. Signup and view all the answers

What initiates the intrinsic pathway of apoptosis?

Cellular stress or damage Signup and view all the answers

How does the Bcl-2 protein influence apoptosis?

It inhibits apoptotic signaling pathways. Signup and view all the answers

Which of the following best describes the extrinsic pathway of apoptosis?

It is triggered by external death ligands. Signup and view all the answers

What major role do initiator caspases play in the process of apoptosis?

They activate the executioner caspases. Signup and view all the answers

Which proteins are among the substrates that are cleaved by executioner caspases?

Nuclear lamins and cell-cell adhesion proteins Signup and view all the answers

What is the consequence of the caspase-mediated cleavage of iCAD?

This leads to the activation of CAD. Signup and view all the answers

What initiates the extrinsic pathway of apoptosis?

Activation of Fas receptors Signup and view all the answers

Which component is released from mitochondria during intrinsic apoptosis?

Cytochrome C Signup and view all the answers

How do survival factors influence apoptosis?

They activate transcription factors. Signup and view all the answers

What role does caspase-8 play in the apoptosis process?

It cleaves other executioner caspases. Signup and view all the answers

Which protein is known as an anti-apoptotic factor?

Bcl2 Signup and view all the answers

Which is a characteristic feature of the intrinsic pathway of apoptosis?

Release of cytochrome C from mitochondria Signup and view all the answers

What is the function of the apoptosome in apoptosis?

To recruit and activate procaspases Signup and view all the answers

What is the primary distinction between intrinsic and extrinsic pathways of apoptosis?

Intrinsic is cell-triggered while extrinsic is receptor-mediated. Signup and view all the answers

What role do Bax/Bak proteins play in apoptosis?

They mediate the release of cytochrome C. Signup and view all the answers

Which of the following is a consequence of the activation of executioner caspases during apoptosis?

Cleavage of cellular proteins leading to cell death Signup and view all the answers

What does the term 'calcium signaling' refer to in the context of apoptosis?

An increase in intracellular calcium that can promote apoptosis Signup and view all the answers

How do transcription factors regulate apoptosis?

By binding to DNA and regulating gene transcription Signup and view all the answers

Which statement correctly describes the relationship between pro-apoptotic and anti-apoptotic factors?

The balance between them determines cell survival. Signup and view all the answers

Study Notes

Apoptosis

Apoptosis is a form of programmed cell death, a process that removes unwanted or damaged cells without causing inflammation.
Apoptosis can be triggered by two pathways: extrinsic and intrinsic.

Extrinsic Pathway

The extrinsic pathway is triggered by external signals, such as death receptors (like Fas receptor) activated by Fas ligand on killer lymphocytes.
This activation leads to the formation of a death-induced signaling complex (DISC) which involves the recruitment of adaptor proteins and initiator procaspases.
DISC facilitates the dimerization of an initiator procaspase (caspase-8), leading to its activation.
Activated caspase-8, in turn, activates executioner caspases, triggering apoptosis.

Intrinsic Pathway

The intrinsic pathway is triggered by internal signals, such as damage or absence of critical survival factors.
Mitochondria play a key role by releasing cytochrome C.
Cytochrome C activates an adaptor protein, leading to the formation of a wheel-like heptamer of adaptor proteins called the apoptosome.
The apoptosome recruits and activates initiator procaspases, leading to caspase activation and apoptosis.

Survival Factors

Survival factors can suppress apoptosis and ensure that cells only die when necessary.
Survival factors bind to cell surface receptors, triggering a signaling cascade that activates transcription factors.
These transcription factors stimulate the production of anti-apoptotic proteins, like Bcl2.
Bcl2 inhibits apoptosis by preventing the release of cytochrome C from mitochondria.

Pro- and Anti-Apoptotic Factors

Pro- and anti-apoptotic proteins belong to the same family, the Bcl2 family.
Anti-apoptotic proteins like Bcl2 and others prevent apoptosis, while pro-apoptotic proteins like Bax/Bak promote apoptosis.

Caspases

Caspases are proteases that are essential for apoptosis.
They exist as inactive precursors called procaspases.
Procaspases are activated through a cascade of cleavages and rearrangements.
Initiator caspases activate executioner caspases, which cleave substrates and dismantle cellular components.

Executioner Caspases and Targets

Executioner caspases cleave over a thousand different proteins, including:
- Nuclear lamins, leading to the breakdown of the nuclear envelope.
- Cytoskeletal components, resulting in the collapse of cellular structure.
- Cell-cell adhesion proteins, causing detachment from neighboring cells.

DNA Fragmentation

The CAD nuclease (caspase-activated DNase) is involved in DNA fragmentation during apoptosis.
CAD is normally bound by an inhibitor called iCAD.
Executioner caspases cleave iCAD, activating CAD and triggering DNA fragmentation.

Necrosis vs. Apoptosis

Necrosis is a form of cell death that is characterized by cell swelling and rupture, leading to the release of cellular contents and inflammation.
Apoptosis is a controlled form of cell death that involves the dismantling of cellular components without causing inflammation.

Phagocytosis

Phagocytic cells, like macrophages, play a role in scavenging dead and damaged cells and cell debris.
Phagocytic cells also remove the membrane-enclosed fragments of cells undergoing apoptosis, preventing cell death by necrosis.

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Description

This quiz explores the concept of apoptosis, focusing on its role as programmed cell death. You will learn about the two main pathways of apoptosis: the extrinsic and intrinsic pathways, including their mechanisms and key players. Test your understanding of this critical biological process.