Cell Death: Apoptosis and Necrosis

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Questions and Answers

What is the primary function of apoptosis in the human body?

To repair damaged DNA

To maintain tissue homeostasis and eliminate damaged cells (correct)

To slow down cell division

To eliminate cancer cells

What is the estimated number of cells that die each day in the human adult?

20 billion

50 billion (correct)

100 billion

10 billion

What is a characteristic of cancer cells?

They avoid apoptosis to arise as tumors (correct)

They divide slowly

They are impervious to DNA damage

They undergo excessive apoptosis

What is autophagy?

One of the three types of cell death Signup and view all the answers

What is the result of too much or too little apoptosis?

Either neurodegenerative disorders or cancer Signup and view all the answers

How much of cells does the human body replace each year?

70 kg Signup and view all the answers

What occurs within minutes of the apoptotic trigger?

Dilatation of the endoplasmic reticulum and chromatin condensation Signup and view all the answers

Which pathway is also known as the 'death receptor pathway'?

Extrinsic pathway Signup and view all the answers

What is the timeframe for the energy-independent form of cell death?

12–24 hours Signup and view all the answers

What is the result of the loss of function of mitochondria and endoplasmic reticulum?

Dramatic breakdown of energy supply leading to cellular, nuclear, and organellar swelling Signup and view all the answers

What occurs in the later stages of apoptosis?

Budding of cell membrane and release of lysosomal enzymes Signup and view all the answers

What is the outcome of the release of lysosomal enzymes in apoptosis?

Triggering of an inflammatory response Signup and view all the answers

What is the primary function of AIF released by MOMP?

To contribute to chromatin condensation and large-scale DNA degradation Signup and view all the answers

What is the role of APAF-1 in the apoptosome?

To create the apoptosome complex Signup and view all the answers

What is the function of the WD40 motif in APAF-1?

To negatively regulate APAF-1 Signup and view all the answers

What is the consequence of cytochrome c release from mitochondria?

Activation of procaspase-9 Signup and view all the answers

What is the role of EndoG released by MOMP?

To aid the caspase-activated DNase in nucleosomal DNA fragmentation Signup and view all the answers

What is the function of the CARD domain in APAF-1?

To interact with procaspase-9 Signup and view all the answers

What is the primary function of the WD40 repeats in the C-terminal region of APAF-1?

To keep the APAF-1 protein in an inactive state until cytochrome c is present Signup and view all the answers

What is the consequence of APAF-1 switching from a 'closed' to an 'open' conformation?

An increase in the binding activity of dATP/ATP Signup and view all the answers

What is the function of the apoptosome?

To recruit procaspase-9 into its central hub and activate it Signup and view all the answers

What is the characteristic of caspases that allows them to selectively cleave proteins?

Their ability to cleave proteins after aspartate residues Signup and view all the answers

What is the role of initiator caspases?

To activate downstream executioner caspases Signup and view all the answers

What is the outcome of the activation of downstream executioner caspases?

Cell death Signup and view all the answers

What is the primary function of Fas ligand in the regulation of the immune system?

To induce apoptosis Signup and view all the answers

What is the outcome of the mitochondrial pathway of apoptosis?

Release of pro-apoptotic proteins Signup and view all the answers

What is the role of BID in apoptosis?

Facilitation of death receptor-mediated apoptosis Signup and view all the answers

What is the function of MOMP during apoptosis?

To release inhibitors of IAPs Signup and view all the answers

What is the primary function of APAF-1?

To activate caspases Signup and view all the answers

Which pathway is responsible for the majority of apoptosis in vertebrates?

Mitochondrial pathway Signup and view all the answers

Study Notes

Cell Death

There are three types of cell death: apoptosis, necrosis, and autophagy
Apoptosis is a characteristic form of programmed cell death, essential for development, maintenance of tissue homeostasis, and elimination of damaged cells
50 billion or more cells die each day in the human adult, and each person replaces around 70 kg of cells every year

Apoptosis

Apoptosis is a fundamental process that can lead to diseases such as neurodegenerative disorders or cancer if it occurs too much or too little
Cancer cells must avoid apoptosis for tumors to arise
Apoptosis is an active, energy-requiring process leading to a characteristic series of morphological changes that accompany the degradation of the cell

Signal Transduction Pathways that Mediate Apoptosis

There are two pathways that trigger apoptosis: the extrinsic (death receptor pathway) and intrinsic (mitochondrial) apoptotic pathways
The extrinsic pathway is activated by the engagement of death receptors on the cell surface
The intrinsic pathway involves the release of cytochrome c and other proteins from the mitochondria

Apoptosome

The apoptosome is a complex that activates procaspase-9 and is composed of cytochrome c, APAF-1, and procaspase-9
APAF-1 contains a nucleotide binding domain (NBD), a caspase recruitment domain (CARD), and a long C-terminal extension containing 13 repeats of the WD40 motif
Formation of the apoptosome leads to the activation of procaspase-9, which can go on to activate downstream executioner caspases

Caspases

Caspases are highly selective cysteine proteases that have a preference for cleaving proteins after aspartate residues
Caspases can be grouped into two categories: initiator caspases and effector (or executioner) caspases
Initiator caspases (e.g. caspase-9) activate effector caspases (e.g. caspase-3 and caspase-7), which eventually lead to cell death

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Description

Learn about the differences between apoptosis and necrosis, two types of cell death. Understand the characteristics of apoptosis, including chromatin condensation and DNA fragmentation, and how it differs from necrosis. Test your knowledge of cellular processes!