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Questions and Answers
What is one of the key roles of programmed cell death during animal development?
What is one of the key roles of programmed cell death during animal development?
Which of the following disorders has been linked to abnormalities in programmed cell death?
Which of the following disorders has been linked to abnormalities in programmed cell death?
Why is a balance between cell death and cell renewal important in adult organisms?
Why is a balance between cell death and cell renewal important in adult organisms?
What can potentially replace damaged tissues in adult organisms?
What can potentially replace damaged tissues in adult organisms?
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What initiates the complex process of animal development?
What initiates the complex process of animal development?
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What is the primary purpose of apoptosis in an organism?
What is the primary purpose of apoptosis in an organism?
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How does apoptosis differ from necrosis in cellular response?
How does apoptosis differ from necrosis in cellular response?
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What are the observable characteristics of a cell undergoing apoptosis?
What are the observable characteristics of a cell undergoing apoptosis?
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The term 'apoptosis' is derived from which of the following Greek concepts?
The term 'apoptosis' is derived from which of the following Greek concepts?
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During what stages of an organism's life does apoptosis occur?
During what stages of an organism's life does apoptosis occur?
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Study Notes
Programmed Cell Death (Apoptosis)
- Apoptosis is a controlled process of cellular suicide
- Occurs as a normal part of an organism's growth and development
- The body uses apoptosis to get rid of unneeded or abnormal cells
- The term apoptosis is derived from the Greek word describing the falling of leaves
- It is distinguished from accidental cell death caused by injury or inflammation
Animal Development
- Animal development starts with rapid proliferation of embryonic cells.
- These cells then differentiate into specialized cell types.
- This process creates the various tissues and organs of the adult organism.
- Humans have approximately 1014 cells with more than 200 differentiated cell types.
- Development begins with a single fertilized egg.
Cell Death and Proliferation
- Cell death and proliferation are balanced throughout the life of multicellular organisms.
- The balance is important for development and maintaining tissue health.
Types of Cell Death
- Apoptosis: A normal, controlled process where cells die by programmed cell death.
- Necrosis: Cell death resulting from injury, characterized by swelling, lysis, and inflammation.
Apoptosis Characteristics
- Neighboring cells remain healthy during apoptosis
- Apoptotic cell death doesn't typically lead to an inflammatory response
- Apoptotic bodies (cell fragments) are efficiently phagocytosed (engulfed) by neighboring cells and macrophages.
- It is an active process involving a series of cellular changes that lead to the death of the cell.
Apoptosis and Illnesses
- Abnormalities in apoptosis are linked to various illnesses, including cancer, autoimmune diseases, and neurodegenerative disorders (Parkinson's and Alzheimer's disease).
Cell Renewal
- In adult tissues, cell death must be balanced by cell renewal.
- Stem cells in tissues are capable of replacing lost cells.
- The ability of stem cells to differentiate into diverse cell types is crucial for tissue repair and maintenance.
- Embryonic stem cells are of great interest for therapeutic use in damaged tissues.
Apoptosis Pathway
- Two pathways are involved in apoptosis: Intrinsic and Extrinsic.
Intrinsic Pathway
- Activated by internal surveillance mechanisms signals (or not sent) from other cell
- Includes DNA damage, chemical exposure, interference with cellular pathways, and excessive cell-cycle activation.
Extrinsic Pathway
- Triggered by signals from other cells (external input),
- Killer cells directly interact with target cells.
- Target cell receptors activate specific pathways starting at the plasma membrane.
Apoptosis and the Immune System
- In the immune system, apoptosis is crucial for controlling cell populations.
- Cytotoxic T lymphocytes use apoptosis to eliminate infected cells.
- This prevents viral replication and spread.
Apoptosis and Cancer
- DNA damage can induce apoptosis, eliminating cells with potentially harmful mutations and preventing cancer development.
The Bcl-2 Family
- Proteins in this family are crucial regulators of apoptosis.
- This family has anti-apoptotic and pro-apoptotic members.
- These proteins interact to control cell death.
Apoptosis in Healthy Cells
- BAK is associated with the mitochondrial outer membrane (in healthy cells).
- BAX is located in the cytoplasm (in healthy cells).
Mechanisms of apoptosis
- Cytochrome C plays a key role in apoptosis.
- In the intrinsic pathway, cytochrome C is released from mitochondria, activates caspase proteins which lead to cell death.
- In the extrinsic pathway, Fas ligand activates caspase 8 to induce apoptosis.
Apaf-1
- Apaf-1 is a crucial protein in the intrinsic apoptosis pathway.
- Its conformational change allows for apoptosome formation.
- Binding to caspase 9 triggers activation and initiates the caspase cascade.
In the Cytoplasm
- Cytochrome C binds to Apaf-1 (apoptotic protease-activating factor-1), altering its conformation.
- This exposure allows Apaf-1 to form the apoptosome structure.
Apoptosis and Cell Death
- Apoptosis eliminates a cell neatly without causing inflammation, eliminating the defective cell.
- Cells that die due to injury swell and rupture and cause cell death.
Intrinsic Pathway
- Signal molecules (Bax, Bak) start the process by acting on the mitochondria.
- Cytochrome c release and caspase activation lead to Programmed Cell Death.
- Anti-apoptotic molecules (Bcl-2, Bcl-xL) inhibit mitochondria and prevent caspase activation thus preventing apoptosis.
- Binding of anti-apoptotic molecules to Bax/Bak prevents mitochondrial outer membrane permeabilization.
BH3-Only Family Proteins
- BH3-only proteins can directly or indirectly promote death by facilitating Bax/Bak oligomerization or binding/neutralizing anti-apoptotic Bcl-2 proteins.
Additional Factors
- Withdrawal of nutrients or survival signals from the environment can trigger apoptosis.
- Growth factors.
- Contact with neighboring cells
- The extracellular matrix are all important factors for cell survival or triggering cell death.
Common Causes of Programmed Cell Death
- Defective cells
- Cells overproduced
- Cells without function
- Cells with abnormal cell cycle
- Virus-infected cells
- Treatment with chemotherapy
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Description
Explore the key concepts of programmed cell death, known as apoptosis, and its essential role in organism growth and development. This quiz covers the processes of cell proliferation and differentiation, highlighting their significance in maintaining tissue health. Test your understanding of these vital biological processes and their implications in animal development.
