Cell Biology: Cell Death and Apoptosis

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Questions and Answers

What is the primary difference between apoptosis and necrosis?

Apoptosis occurs due to lack of ATP, while necrosis occurs due to physical damage.

Apoptosis is regulated cell death, while necrosis is accidental cell death. (correct)

Apoptosis occurs due to physical damage, while necrosis occurs due to lack of ATP.

Apoptosis is accidental cell death, while necrosis is regulated cell death.

What is the role of apoptosis in tissue remodeling and development?

To promote cell growth and division.

To induce necrosis in adjacent cells.

To remove excess cells and form mature tissues. (correct)

To trigger inflammatory responses.

What is a characteristic of necrosis?

Cells die due to lack of ATP or physical damage. (correct)

Cell contents are not released into the extracellular space.

Cells die in a controlled manner.

No inflammatory response is triggered.

What is the term for the process by which cells die in a controlled manner?

Programmed Cell Death (PCD) Signup and view all the answers

What is the result of apoptosis in terms of inflammatory response?

No inflammatory response is triggered. Signup and view all the answers

What is the term for the process by which cells die due to lack of ATP or physical damage?

Accidental Cell Death (ACD) Signup and view all the answers

What is the result of necrosis in terms of cell contents?

Cell contents are released into the extracellular space. Signup and view all the answers

What is a trigger of apoptosis?

Intrinsic or extrinsic signals. Signup and view all the answers

What is the primary function of iCAD?

Inhibition of CAD endonuclease Signup and view all the answers

What is the result of DNA fragmentation during apoptosis?

Cleavage of DNA in the regions between nucleosomes Signup and view all the answers

What triggers the caspase cascade in the extrinsic pathway?

Binding of Fas ligand to Fas receptor Signup and view all the answers

What is the function of executioner caspases?

Degradation of iCAD Signup and view all the answers

What is the name of the complex formed after the binding of Fas ligand to Fas receptor?

Death-inducing signalling complex (DISC) Signup and view all the answers

What is the name of the receptor family that death receptors belong to?

Tumour necrosis factor (TNF) family Signup and view all the answers

What is the result of caspase degradation of iCAD?

Activation of CAD endonuclease Signup and view all the answers

What is the name of the process triggered from outside the cell?

Extrinsic pathway Signup and view all the answers

What is the primary function of phosphatidylserine in apoptosis?

To facilitate phagocytosis by macrophages Signup and view all the answers

What is the role of survival factors in apoptosis?

They block apoptosis by binding to cell surface receptors Signup and view all the answers

What is the primary function of apoptosis in response to excessive DNA damage?

To prevent the possible development of cancer by removing damaged cells Signup and view all the answers

What is the outcome of caspase activation in apoptosis?

Flipping of phosphatidylserine to the outer leaf of the plasma membrane Signup and view all the answers

What type of radiation induces chemical bonds between adjacent thymines, leading to thymine dimers?

UVB (290-320nm) Signup and view all the answers

What is the consequence of Bax/Bak aggregation?

Activation of caspases Signup and view all the answers

What is the primary function of initiator caspases in the apoptotic pathway?

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

Why are survival factors important during development?

They block apoptosis to regulate cell number Signup and view all the answers

What is the result of thymine dimers on DNA structure?

Disruption of DNA structure and interference with accurate replication Signup and view all the answers

What is the importance of phagocytosis in apoptosis?

It removes apoptotic cells to maintain tissue homeostasis Signup and view all the answers

What is the fate of apoptotic cells?

They are engulfed and destroyed by phagocytosis by macrophages Signup and view all the answers

What is the morphological change observed during apoptosis where the cell surface bulges?

Blebbing Signup and view all the answers

What is the role of executor caspases in the apoptotic pathway?

To activate all the changes in cell biology observed in apoptosis Signup and view all the answers

What is the result of excessive DNA damage on skin keratinocytes?

They undergo apoptosis and form 'sunburn cells' Signup and view all the answers

What is the primary mechanism that contributes to the development of cancers?

Increase in cell division or decrease in apoptosis Signup and view all the answers

What is often found at the centre of solid tumours?

A necrotic core due to lack of blood supply Signup and view all the answers

What is the result of a decrease in apoptosis in the development of cancers?

An increase in the number of cells Signup and view all the answers

What is a key factor that regulates the development of cancers?

Survival factors Signup and view all the answers

What is the primary mechanism that leads to the development of solid tumours?

Mutations and subsequent development by further mutations Signup and view all the answers

What is the importance of apoptosis in the development of cancers?

It inhibits the development of cancers Signup and view all the answers

Study Notes

Cell Death

Apoptosis: Regulated cell death (RCD) or Programmed Cell Death (PCD) where cells die in a controlled way, and their contents are not released, triggering no inflammatory response.
Necrosis: Accidental cell death (ACD) due to lack of ATP, physical damage, or injury, where cell contents are released, triggering an inflammatory response.

Role of Apoptosis

In tissue re-modelling and development: Removes excess cells to form mature tissues, e.g., during metamorphosis, limb development, and establishment of the adaptive immune system.
In removing damaged cells: Prevents cancer development by eliminating cells with excessive DNA damage, such as those exposed to UVB radiation.

Morphological Changes during Apoptosis

Cells become smaller
Cytoskeleton collapses
Nuclear envelope disassembles
Chromatin condenses and is fragmented
Cell surface bulges (blebs)
Cells break up into membrane-bound "apoptotic bodies"
Apoptotic bodies are engulfed and destroyed by phagocytosis by macrophages

Caspases – Intracellular Mediators of Apoptosis

A family of proteases that trigger a sequence of intracellular events leading to apoptosis
Initiator caspases:Inactive monomers in the cytosol that are activated by cleavage during apoptosis
Executor caspases: Activated by initiator caspases, which then activate all the changes in cell biology observed in apoptosis

DNA Fragmentation

Activated by caspases, which cleave and activate the endonuclease CAD
DNA is cleaved in the regions between nucleosomes, resulting in a ladder of fragments

Extrinsic Pathway to Trigger Apoptosis

Activation of death receptors on the cell surface, such as the Fas receptor
Binding of Fas ligand to the Fas receptor activates the caspase cascade

Removal of Apoptotic Cell by Macrophage

Cells undergoing apoptosis are detected and removed by phagocytosis
Phosphatidylserine (PS) is flipped to the outer leaf of the plasma membrane, triggering phagocytosis

Survival Factors

Block apoptosis by interfering with Bax/Bak aggregation
Examples: Bcl2
Most cells require continuous signalling by survival factors produced by neighbouring cells to block apoptosis

Apoptosis and Cancer

Cancers are caused by an excessive number of cells due to mutations and decreased apoptosis
Increase in cell division or decrease in apoptosis can contribute to cancer development
At the centre of solid tumours, a necrotic core often forms due to a lack of blood supply

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Description

Understand the differences between necrosis and apoptosis, and learn about the intracellular pathways involved in these cell death processes. Appreciate the clinical importance of apoptosis.