Cell Death and Apoptosis Overview

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Questions and Answers

What is the primary purpose of cell death in diseased or damaged cells?

To ensure removal before posing a health threat (correct)

To cause cellular growth in surrounding tissues

To promote inflammation for repair

To stimulate nearby cell division

Which of the following statements about cell death during development is accurate?

It affects the size and shape of limbs and tissues. (correct)

It occurs randomly without any regulatory pattern.

It plays no role in determining tissue size.

It helps in repairing damaged tissues.

How does apoptosis contribute to maintaining tissue or organ size?

By causing continuous growth without regulation

By balancing cell division with cell death rates (correct)

By increasing the rate of cell division significantly

By eliminating all surrounding cells to allow expansion

What characterizes necrosis compared to apoptosis?

It results in the swelling and eventual bursting of cells Signup and view all the answers

What potential consequence can arise from an imbalance between cell division and apoptosis?

Development of cancer Signup and view all the answers

What happens to cells during the process of apoptosis?

They undergo fragmentation into membrane-enclosed bodies Signup and view all the answers

What role does apoptosis play in response to drug treatment in liver cells?

It prevents liver enlargement after drug withdrawal Signup and view all the answers

Which of the following best describes the process of apoptosis?

A programmed process involving shrinking of cells Signup and view all the answers

What key difference distinguishes necrosis from apoptosis?

Apoptosis maintains cell membrane integrity. Signup and view all the answers

Which statement accurately describes the role of caspases in apoptosis?

Executioner caspases cleave substrates to facilitate apoptosis. Signup and view all the answers

How do phagocytic cells contribute to the process of apoptosis?

They scavenge dead cells and cell debris. Signup and view all the answers

What is the function of initiator caspases in the apoptotic process?

To activate executioner caspases. Signup and view all the answers

What happens to the membrane-enclosed fragments of cells undergoing apoptosis?

They are rapidly phagocytosed by immune cells. Signup and view all the answers

What role does Bcl2 play in preventing apoptosis?

Inhibits Bax/Bak aggregation Signup and view all the answers

What happens to Bcl2 upon an apoptotic stimulus?

It is inhibited, leading to apoptosis Signup and view all the answers

What can excessive apoptosis result in?

Tissue damage due to loss of essential cells Signup and view all the answers

Which scenario indicates the consequence of too little apoptosis?

Overproduction of anti-apoptotic proteins in cancer cells Signup and view all the answers

What triggers Bax/Bak to aggregate on the mitochondrial membrane?

An apoptotic stimulus leading to Bcl2 inhibition Signup and view all the answers

Which statement reflects the importance of apoptosis in cellular health?

Apoptosis is necessary in moderation for maintaining cellular balance. Signup and view all the answers

How does Bcl2 contribute to cancer progression?

By inhibiting apoptosis to allow excessive cell proliferation Signup and view all the answers

What is the primary role of cytochrome C in apoptosis?

To activate caspases leading to cell death Signup and view all the answers

Which mechanism initiates apoptosis in response to damaged cells signaling through death receptors?

Formation of the death induced signaling complex (DISC) Signup and view all the answers

What role does cytochrome C play in intrinsic apoptosis?

It activates adaptor proteins for apoptosome assembly Signup and view all the answers

Which statement regarding extrinsic apoptosis is true?

It relies on the activation of death receptors on the cell membrane. Signup and view all the answers

What is the primary function of Bcl2 proteins in relation to apoptosis?

To inhibit apoptosis and enhance cell survival Signup and view all the answers

What initiates the signaling cascade leading to apoptosis when survival factors are bound to cell surface receptors?

Activation of transcription factors Signup and view all the answers

In the context of apoptosis, what does the apoptosome signify?

An assembly of adaptor proteins leading to caspase activation Signup and view all the answers

How do Bax and Bak proteins contribute to intrinsic apoptosis?

By mediating the release of cytochrome C Signup and view all the answers

What is the role of executioner caspases in apoptosis?

To cleave and activate other caspases Signup and view all the answers

Which pathway is characterized by the activation of Fas receptors?

Extrinsic apoptosis pathway Signup and view all the answers

What is a key difference between intrinsic and extrinsic apoptosis?

Intrinsic apoptosis is triggered by internal cellular stress factors. Signup and view all the answers

What determines whether a cell will undergo apoptosis or survive?

The imbalance between pro-apoptotic and anti-apoptotic factors Signup and view all the answers

What is the importance of the survival factors in the apoptosis process?

They bind to cell receptors and inhibit apoptosis. Signup and view all the answers

Which component of apoptosis is primarily responsible for caspase activation?

Death induced signaling complex (DISC) Signup and view all the answers

The term 'caspase' in the context of apoptosis generally refers to:

Enzymes that execute the death program in cells Signup and view all the answers

What is the state of initiator procaspases prior to activation during apoptosis?

Inactive monomers Signup and view all the answers

What role do adaptor proteins play in the activation of procaspases?

They facilitate the dimerization of procaspases. Signup and view all the answers

What is the process referred to as 'cross-cleavage' in the context of caspase activation?

One domain of a dimer cleaving the other domain. Signup and view all the answers

Which of the following correctly describes executioner procaspases?

They become active after cleavage by initiator caspases. Signup and view all the answers

Which of the following cellular components is NOT affected by caspase activity?

Mitochondrial membranes Signup and view all the answers

What is the result of executioner caspases cleaving the inhibitor of CAD nuclease?

Triggering of DNA fragmentation. Signup and view all the answers

What characterizes the intrinsic pathway of apoptosis compared to the extrinsic pathway?

It begins with internal cellular stress signals. Signup and view all the answers

What is a common feature of procaspases in cells under normal conditions?

They are present as inactive precursors. Signup and view all the answers

Which of the following proteins does NOT participate in the cleavage process by caspases during apoptosis?

Cell surface receptors Signup and view all the answers

How does the arrangement of subunits contribute to the activation of caspases?

Rearrangement leads to the formation of the active caspase complex. Signup and view all the answers

Study Notes

Cell Death

Cells can die by necrosis or apoptosis.
Necrosis is messy and often triggers an inflammatory response.
Apoptosis is clean and tidy and does not trigger a response.

Apoptosis - Programmed Cell Death

Cells shrink, cytoskeleton collapses, nuclear envelope disassembles, and DNA is fragmented.
The cell surface becomes chemically altered and the dying cell breaks into membrane- enclosed fragments.
Membrane-enclosed fragments are quickly disposed of by phagocytosis.

Caspases: Proteases Required for Apoptosis

There are two main types of caspases: initiator and executioner.
Initiator caspases initiate apoptosis.
Executioner caspases cleave substrates to dismantle the cell.

Caspase Activation during Apoptosis

Caspases are present in cells as inactive precursors (procaspases).
Initiator procaspases exist as inactive monomers and adaptor proteins facilitate dimerization.
Executioner procaspases exist as inactive dimers and are cleaved by the initiator caspases.

Proteins Cleaved by Caspases

Nuclear lamins breakdown the nuclear envelope.
Components of the cytoskeleton collapse cellular structures.
Cell-cell adhesion proteins are detached from neighboring cells.
When an inhibitor of the CAD nuclease is cleaved, this triggers DNA fragmentation by CAD.

Extrinsic vs. Intrinsic Apoptosis

Extrinsic apoptosis is induced by external signals that tell the cell to die.
Intrinsic apoptosis occurs when the cell responds to damage or the absence of critical survival factors.

Extrinsic Pathway of Apoptosis

Damaged cells express death receptors (Fas receptor).
Fas receptors are activated by Fas ligand on killer lymphocytes.
DISC (death induced signaling complex) is formed in the damaged cell, which enables dimerization of an initiator procaspase (caspase-8), which facilitates its cross-cleavage and activation.
Activated caspase-8 cleaves executioner caspases, triggering apoptosis.

Intrinsic Apoptosis

Activated mitochondria play a key role in intrinsic apoptosis by releasing cytochrome C.
Cytosolic cytochrome C activates an adaptor protein that leads to apoptosome assembly.
The apoptosome activates initiator pro-caspases.
The apoptosome recruits and activates initiator pro-caspases.

Survival Factors Can Inhibit Apoptosis

Survival factors bind to cell surface receptors.
This triggers a signaling cascade that leads to activation of a transcription factor that stimulates the production of Bcl2.
Bcl2 is an anti-apoptotic protein.

Balance Between Pro- and Anti-Apoptotic Factors

Pro and anti-apoptotic proteins belong to the Bcl2 family.
Anti-apoptotic Bcl2 family proteins (Bcl2 itself and others) inhibit the formation of channels that release cytochrome C.
Pro-apoptotic Bcl2 family proteins (e.g. Bax, Bak) release cytochrome C.

Bcl2 Inhibits Bax/Bak

Bcl2 inhibits Bax/Bak, preventing cytochrome C.
Bax/Bak must oligomerize to form channels that can release cytochrome C.

Too Much Or Too Little Apoptosis

Too much apoptosis leads to tissue damage.
Examples: heart attacks, strokes.
Prevention of normal cell death occurs in many cancers.
Some cancer cells overproduce anti-apoptotic Bcl2 and suppress apoptosis, leading to tumor formation.

Apoptosis

Apoptosis is a beautiful, controlled process with many applications in our bodies.

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Description

Explore the mechanisms of cell death including necrosis and apoptosis. Learn about the roles of caspases in programmed cell death and the differences between these two processes. This quiz will help you understand the cellular changes that occur during apoptosis.