mol bio lecture 5 pt2

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Questions and Answers

What role does p53 play in the intrinsic pathway of apoptosis?

It inhibits the expression of pro-apoptotic proteins.

It directly cleaves caspases to initiate apoptosis.

It promotes the release of anti-apoptotic factors from mitochondria.

It upregulates the expression of pro-apoptotic proteins like Bax. (correct)

How do Bax and Bak contribute to the intrinsic pathway of apoptosis?

They bind to cytochrome c, preventing its release.

They form pores in the mitochondrial membrane. (correct)

They inhibit the caspase cascade directly.

They enhance the activity of anti-apoptotic proteins.

What is the primary function of the apoptosome in the intrinsic apoptotic pathway?

To form a complex that activates procaspase-9. (correct)

To inhibit mitochondrial permeabilization.

To prevent the activation of procaspase-9.

To cleave essential cellular proteins.

What is the consequence of mitochondrial outer membrane permeabilization (MOMP) in the intrinsic apoptotic pathway?

It leads to the release of pro-apoptotic factors into the cytoplasm. Signup and view all the answers

What distinguishes apoptosis from necrosis regarding the impact on DNA?

Apoptosis leads to DNA fragmentation, while necrosis does not. Signup and view all the answers

What is the role of Bcl-2 in the intrinsic pathway of apoptosis?

It inhibits pro-apoptotic factors like Bax. Signup and view all the answers

Which statement best describes the caspase cascade in apoptosis?

It involves the sequential activation of caspases leading to cell death. Signup and view all the answers

In the context of the intrinsic apoptotic pathway, how does oxidative stress influence the process?

It triggers the activation of p53 and promotes apoptosis. Signup and view all the answers

What is the role of FasL in the extrinsic pathway of apoptosis?

It binds to Fas receptor, initiating the apoptotic signal. Signup and view all the answers

Which caspase is primarily responsible for initiating the execution phase of apoptosis?

Caspase-8 Signup and view all the answers

What triggers the release of cytochrome c from the mitochondria?

Mitochondrial outer membrane permeabilization Signup and view all the answers

Which of the following statements accurately describes the formation of the Death-Inducing Signaling Complex (DISC)?

It requires the binding of adaptor proteins like FADD to the receptor's death domain. Signup and view all the answers

What is the function of Bid within the extrinsic pathway of apoptosis?

It links the extrinsic and intrinsic pathways by promoting mitochondrial changes. Signup and view all the answers

What role does Smac/DIABLO play in the apoptosis process?

It neutralizes inhibitors of apoptosis proteins Signup and view all the answers

Which of the following best describes the function of caspase-activated DNase (CAD) in apoptosis?

It cleaves DNA at internucleosomal regions Signup and view all the answers

How do executioner caspases contribute to the process of apoptosis?

They cleave structural proteins, leading to cell disassembly. Signup and view all the answers

Which stage of apoptosis involves the formation of small membrane-bound vesicles?

DNA Fragmentation and Cell Dismantling Signup and view all the answers

What triggers the activation of caspase-8 in the extrinsic apoptotic pathway?

The recruitment of adaptor proteins like FADD to the receptor death domain. Signup and view all the answers

Which of the following is NOT a characteristic of the caspase cascade in apoptosis?

Initiator caspases are only activated by apoptotic stimuli. Signup and view all the answers

How does apoptosis differ from necrosis in terms of intracellular content release?

Apoptosis prevents the release of intracellular contents Signup and view all the answers

Which caspase is primarily responsible for initiating the apoptosis process?

Caspase-8 Signup and view all the answers

What critical role do mitochondria play in the intrinsic pathway of apoptosis?

They release cytochrome c which initiates apoptosis. Signup and view all the answers

What is a primary characteristic of the DNA fragmentation that occurs during apoptosis?

It leads to a ladder pattern during gel electrophoresis Signup and view all the answers

Which protein is considered part of the tumor necrosis factor receptor family involved in the extrinsic pathway?

Fas (CD95) Signup and view all the answers

What is the end effect of the caspase cascade during apoptosis?

Dismantling and shrinkage of the cell. Signup and view all the answers

Which of the following phases occurs last in the apoptosis process?

Phagocytosis Signup and view all the answers

What main event is associated with the execution phase of apoptosis?

Chromatin condensation occurs Signup and view all the answers

What is the primary role of autophagy during nutrient scarcity?

To degrade non-essential proteins and organelles for nutrient release Signup and view all the answers

How does autophagy contribute to immune function?

By eliminating intracellular pathogens and aiding antigen presentation Signup and view all the answers

In embryonic development, what role does autophagy play?

It facilitates the transition to specialized cell types by degrading unnecessary components. Signup and view all the answers

What is a primary consequence of necrosis compared to apoptosis?

Necrosis leads to cell lysis and inflammation. Signup and view all the answers

Which process is specifically responsible for the separation of fingers and toes during embryonic development?

Apoptosis Signup and view all the answers

What is the significance of mitophagy in cellular quality control?

It selectively degrades damaged mitochondria to maintain cell function. Signup and view all the answers

In which part of the immune system does apoptosis play a critical role in preventing autoimmunity?

Thymus Signup and view all the answers

How is autophagy correlated with aging and longevity?

It enhances the longevity of cells by maintaining proteostasis. Signup and view all the answers

How does apoptosis contribute to tissue homeostasis in adult organisms?

By balancing cell turnover. Signup and view all the answers

What role does apoptosis have in neuronal development?

It eliminates excess neurons for optimal connectivity. Signup and view all the answers

Which of the following statements best describes autophagy compared to apoptosis?

Autophagy targets and recycles cellular components. Signup and view all the answers

Which statement about the function of apoptosis in the immune system is correct?

It helps restore homeostasis after an immune response. Signup and view all the answers

What is the main outcome of apoptosis during the embryonic stage of development?

Elimination of unnecessary cells. Signup and view all the answers

In what way can necrosis damage surrounding tissues?

By triggering an inflammatory response. Signup and view all the answers

Study Notes

Apoptosis Overview

Apoptosis is a programmed cell death essential for development, tissue maintenance, and immune regulation.
There are two pathways of apoptosis: intrinsic and extrinsic, each having unique mediators and signaling steps.

Intrinsic Pathway (Mitochondrial-Mediated Apoptosis)

Triggered by internal signals: DNA damage, oxidative stress, and other cellular stresses.
Key Mediators:
- p53 activates pro-apoptotic proteins (e.g., Bax and Bak) upon sensing cellular stress.
- Bcl-2 is an anti-apoptotic protein that inhibits Bax and Bak activity, preventing apoptosis.
Key Steps:
- Cellular Stress: Internal signals activate p53, which promotes apoptosis by upregulating Bax and Bak.
- Mitochondrial Outer Membrane Permeabilization (MOMP): Bax and Bak oligomerize, forming pores in the mitochondrial membrane, releasing pro-apoptotic factors like cytochrome c.
- Apoptosome Formation: Cytochrome c binds Apaf-1, leading to the activation of procaspase-9.
- Caspase Cascade Activation: Activated caspase-9 cleaves procaspase-3, which initiates the execution process of apoptosis.

Extrinsic Pathway (Death Receptor-Mediated Apoptosis)

Triggered by external signals through death receptors (e.g., Fas and TNF receptors).
Key Steps:
- Ligand Binding: FasL or TNF-α binds to their respective receptors, recruiting adaptor proteins like FADD.
- Formation of DISC: Recruitment of procaspase-8 occurs, forming the Death-Inducing Signaling Complex.
- Caspase-8 Activation: Procaspase-8 is cleaved to active caspase-8, which activates downstream caspases.
- Cross-Talk with Intrinsic Pathway: Caspase-8 can activate Bid, linking both pathways.

Role of Caspase Cascade

Caspases are cysteine proteases that execute the apoptotic program.
Initiator Caspases: (caspase-8, caspase-9) initiate the apoptotic signal.
Executioner Caspases: (caspase-3, caspase-7) cleave proteins leading to cell dismantling, such as nuclear lamins and cytoskeletal proteins.

Role of Mitochondria

Central to apoptosis, especially in the intrinsic pathway.
Cytochrome c Release: MOMP allows the release of cytochrome c into the cytoplasm, crucial for apoptosome formation and caspase activation.
Releasing Pro-Apoptotic Factors: Mitochondria also release Smac/DIABLO to neutralize inhibitors of apoptosis proteins, promoting apoptosis.

DNA Fragmentation

Activation of CAD: Caspase-activated DNase (CAD) cleaves DNA during apoptosis, generating a ladder pattern of fragments.
Chromatin Condensation: Apoptotic cells undergo chromatin condensation, facilitating DNA fragmentation.
Contrast with Necrosis: Unlike apoptotic DNA fragmentation, necrosis leads to cell swelling and uncontrollable release of cellular contents, causing inflammation.

Timing and Stages of Apoptosis

Apoptosis occurs within a few hours and includes distinct phases:
- Initiation: Activation of initiator caspases.
- Execution: Activation of executioner caspases leading to cellular changes.
- DNA Fragmentation: Endonucleases cleave DNA, forming apoptotic bodies.
- Phagocytosis: Apoptotic bodies are engulfed, preventing inflammation.

Differences from Necrosis

Apoptosis is a controlled, energy-dependent process preventing inflammation through encapsulation of apoptotic bodies.
Necrosis is uncontrolled, causing cell lysis and inflammation through the release of cellular contents.

Role of Apoptosis in Development and Function

Embryonic Development: Shapes tissues, eliminates excess cells and redundant structures (e.g., digits in limb formation).
Immune Regulation: Removes self-reactive cells and excess immune cells post-response to maintain homeostasis.
Tissue Homeostasis: Balances cell proliferation and death, removing damaged or abnormal cells to prevent cancer.

Role of Autophagy in Development and Function

Nutrient Recycling: Autophagy degrades non-essential components during stress, providing energy and nutrients.
Cell Differentiation: Supports differentiation by clearing unnecessary cellular components in developing cells.
Host Defense: Engages in xenophagy to eliminate pathogens and assists in antigen presentation.

Aging and Longevity

Maintains proteostasis and cellular quality control, preventing accumulation of damaged components linked to aging and age-related diseases.
Enhanced autophagy correlates with increased lifespan in various model organisms.

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Description

This quiz explores the intricate processes of apoptosis, focusing on the intrinsic and extrinsic pathways. Key mediators such as Bcl-2 and p53 will be highlighted, along with the significance of the caspase cascade and mitochondria in this programmed cell death. Additionally, the quiz will cover the differences between apoptosis and necrosis, especially regarding DNA consequences.