Cell Biology: Cell Death and Apoptosis
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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?

    <p>Programmed Cell Death (PCD)</p> Signup and view all the answers

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

    <p>No inflammatory response is triggered.</p> 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?

    <p>Accidental Cell Death (ACD)</p> Signup and view all the answers

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

    <p>Cell contents are released into the extracellular space.</p> Signup and view all the answers

    What is a trigger of apoptosis?

    <p>Intrinsic or extrinsic signals.</p> Signup and view all the answers

    What is the primary function of iCAD?

    <p>Inhibition of CAD endonuclease</p> Signup and view all the answers

    What is the result of DNA fragmentation during apoptosis?

    <p>Cleavage of DNA in the regions between nucleosomes</p> Signup and view all the answers

    What triggers the caspase cascade in the extrinsic pathway?

    <p>Binding of Fas ligand to Fas receptor</p> Signup and view all the answers

    What is the function of executioner caspases?

    <p>Degradation of iCAD</p> Signup and view all the answers

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

    <p>Death-inducing signalling complex (DISC)</p> Signup and view all the answers

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

    <p>Tumour necrosis factor (TNF) family</p> Signup and view all the answers

    What is the result of caspase degradation of iCAD?

    <p>Activation of CAD endonuclease</p> Signup and view all the answers

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

    <p>Extrinsic pathway</p> Signup and view all the answers

    What is the primary function of phosphatidylserine in apoptosis?

    <p>To facilitate phagocytosis by macrophages</p> Signup and view all the answers

    What is the role of survival factors in apoptosis?

    <p>They block apoptosis by binding to cell surface receptors</p> Signup and view all the answers

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

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

    What is the outcome of caspase activation in apoptosis?

    <p>Flipping of phosphatidylserine to the outer leaf of the plasma membrane</p> Signup and view all the answers

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

    <p>UVB (290-320nm)</p> Signup and view all the answers

    What is the consequence of Bax/Bak aggregation?

    <p>Activation of caspases</p> Signup and view all the answers

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

    <p>To cleave and activate executor caspases</p> Signup and view all the answers

    Why are survival factors important during development?

    <p>They block apoptosis to regulate cell number</p> Signup and view all the answers

    What is the result of thymine dimers on DNA structure?

    <p>Disruption of DNA structure and interference with accurate replication</p> Signup and view all the answers

    What is the importance of phagocytosis in apoptosis?

    <p>It removes apoptotic cells to maintain tissue homeostasis</p> Signup and view all the answers

    What is the fate of apoptotic cells?

    <p>They are engulfed and destroyed by phagocytosis by macrophages</p> Signup and view all the answers

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

    <p>Blebbing</p> Signup and view all the answers

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

    <p>To activate all the changes in cell biology observed in apoptosis</p> Signup and view all the answers

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

    <p>They undergo apoptosis and form 'sunburn cells'</p> Signup and view all the answers

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

    <p>Increase in cell division or decrease in apoptosis</p> Signup and view all the answers

    What is often found at the centre of solid tumours?

    <p>A necrotic core due to lack of blood supply</p> Signup and view all the answers

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

    <p>An increase in the number of cells</p> Signup and view all the answers

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

    <p>Survival factors</p> Signup and view all the answers

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

    <p>Mutations and subsequent development by further mutations</p> Signup and view all the answers

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

    <p>It inhibits the development of cancers</p> 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.

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