mol bio lecture 5

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Questions and Answers

What is the primary consequence of increased cyclophilin D activity?

Reduced cell survival

Enhanced mitochondrial membrane permeability

Inhibition of mitochondrial potential loss

Increased necrosis or apoptosis (correct)

How does downregulation of Apaf-1 affect apoptosis?

It enhances the release of cytochrome c

It promotes apoptosis by increasing procaspase activity

It blocks the formation of the apoptosome, reducing apoptosis (correct)

It has no effect on apoptosis

What effect does increased MPTP opening have on cell survival?

It leads to necrosis or apoptosis (correct)

It stabilizes mitochondrial potential

It enhances cell survival

It inhibits cytochrome c release

Which of the following statements about Bcl-2 is accurate?

It acts to inhibit pro-apoptotic proteins like Bax Signup and view all the answers

What role does cytochrome c play in apoptosis?

It activates procaspase-9 after forming the apoptosome Signup and view all the answers

What is a consequence of blocking the opening of MPTP?

Inhibition of apoptosis Signup and view all the answers

What happens to apoptotic processes when cyclophilin D is inhibited?

Cell survival is promoted due to reduced permeability Signup and view all the answers

What does the release of cytochrome c indicate in a cell?

Activation of apoptosis pathways Signup and view all the answers

What is the direct consequence of excessive opening of the MPTP?

Loss of mitochondrial potential and swelling Signup and view all the answers

In what way does Bcl-2 contribute to the regulation of apoptosis?

By inhibiting pro-apoptotic proteins like Bax Signup and view all the answers

What is a defining characteristic of necrosis?

It is an uncontrolled process triggered by external factors. Signup and view all the answers

Which of the following best describes the process of apoptosis?

It is highly regulated and avoids inflammatory responses. Signup and view all the answers

Which pathway is NOT involved in apoptosis?

Necrotic pathway linked to uncontrolled cell swelling. Signup and view all the answers

What is a potential result of necrosis on surrounding tissues?

Cell swelling and rupture with subsequent tissue damage. Signup and view all the answers

What is NOT a characteristic feature of apoptosis?

Triggering only through external factors such as trauma. Signup and view all the answers

During which process does cytochrome c play a crucial role?

Apoptosis via the intrinsic pathway. Signup and view all the answers

What is the main outcome of apoptosis, unlike necrosis?

The removal of unnecessary or harmful cells without inflammation. Signup and view all the answers

Which event occurs during necrosis?

Membrane rupture and release of intracellular contents. Signup and view all the answers

Which statement about autophagy is most accurate?

It involves degradation of cellular components for recycling. Signup and view all the answers

Which is true about the extrinsic pathway of apoptosis?

It involves death ligands binding to cell surface receptors. Signup and view all the answers

What is the primary role of caspase-3 in the apoptosis process?

Cleaving cellular substrates to execute apoptosis Signup and view all the answers

Which component initiates the formation of the apoptosome in the intrinsic pathway?

Cytochrome c Signup and view all the answers

What function does the mitochondrial permeability transition pore (MPTP) serve in apoptosis?

Promoting cytochrome c release and leading to cell death Signup and view all the answers

Which protein is critical in regulating the balance between apoptosis and necrosis through MPTP?

Cyclophilin D Signup and view all the answers

How is procaspase-9 activated in the intrinsic apoptosis pathway?

As part of the apoptosome complex formed with Apaf-1 and cytochrome c Signup and view all the answers

What is the primary role of autophagy in cells?

To recycle cellular components during stress Signup and view all the answers

Which statement accurately describes apoptosis compared to necrosis?

Apoptosis is an adaptive process, while necrosis is not Signup and view all the answers

Which caspase is primarily involved in the execution phase of apoptosis?

Caspase-3 Signup and view all the answers

What triggers the intrinsic pathway of apoptosis?

Oxidative stress and DNA damage Signup and view all the answers

What process occurs immediately before the formation of apoptotic bodies?

Cytoskeletal breakdown Signup and view all the answers

Which of the following proteins is involved in the activation of the extrinsic pathway of apoptosis?

Caspase-8 Signup and view all the answers

What is the role of cytochrome c in apoptosis?

To activate the apoptosome and caspase-9 Signup and view all the answers

In apoptosis, how are apoptotic bodies removed from the system?

Through phagocytosis by macrophages Signup and view all the answers

Which process directly involves death domains in apoptosis?

Extrinsic pathway activation Signup and view all the answers

What is a significant consequence of excessive autophagy?

Cell death Signup and view all the answers

What happens when caspase-3 activity is reduced?

Blocked apoptosis, allowing damaged cells to survive. Signup and view all the answers

What is the effect of upregulating procaspase-8?

Enhanced apoptosis through the extrinsic pathway. Signup and view all the answers

What role does caspase-9 play in the intrinsic apoptosis pathway?

It activates downstream apoptotic pathways. Signup and view all the answers

What is the consequence of downregulating Bax?

Blocked mitochondrial outer membrane permeabilization. Signup and view all the answers

What occurs with disrupted formation of the apoptosome?

Blocked activation of caspase-9. Signup and view all the answers

Which outcome is associated with enhanced Bax activity?

More cytochrome c release and enhanced apoptosis. Signup and view all the answers

What is the impact of reduced caspase-8 activity?

Impaired apoptosis and potential for unchecked cell proliferation. Signup and view all the answers

What results from increased levels of cellular caspase-9?

Promotion of apoptosis in response to stress. Signup and view all the answers

Study Notes

Caspase Function and Regulation

Caspase-3: Key executioner in apoptosis. Increased activity promotes apoptosis, while reduced activity allows potentially harmful cells to survive.
Caspase-8: An initiator caspase in the extrinsic pathway; activated by death receptors. Upregulation enhances apoptosis, while downregulation or mutations lead to impaired apoptosis, facilitating tumorigenesis.
Caspase-9: Initiator in the intrinsic pathway, activated by the apoptosome. Increased activity promotes apoptosis; downregulation leads to cell survival, particularly in cancerous conditions.

Pro-Apoptotic and Anti-Apoptotic Factors

Bax: Pro-apoptotic member of Bcl-2 family. Promotes mitochondrial outer membrane permeabilization, facilitating cytochrome c release. Upregulation increases apoptosis, while downregulation inhibits it, enhancing cell survival and cancer risk.
Bcl-2: Anti-apoptotic protein that prevents cytochrome c release by inhibiting pro-apoptotic proteins. Upregulation blocks apoptosis, promoting cell survival.

Apoptosome and Its Role

Apoptosome: Complex formed by Apaf-1, cytochrome c, and procaspase-9. It initiates caspase-9 activation. Disruption prevents apoptosis, while enhanced formation accelerates apoptosis via the intrinsic pathway.

Mitochondrial Dynamics in Cell Death

Cyclophilin D: Regulates the mitochondrial permeability transition pore (MPTP). Upregulation increases cell death via necrosis/apoptosis; its inhibition promotes cell survival.
MPTP: Pore that, when opened, leads to mitochondrial depolarization and release of pro-apoptotic factors, promoting necrosis/apoptosis. Restricted opening enhances survival under stress.

Cytochrome c and Apaf-1 Function

Cytochrome c: Released from mitochondria during apoptosis. It binds to Apaf-1 to form the apoptosome, driving apoptosis. Its release correlates with increased apoptosis; sequestration leads to reduced apoptosis.
Apaf-1: Activates procaspase-9 when bound to cytochrome c, forming the apoptosome. Increased activity enhances apoptosis; decreased activity blocks it, promoting cell survival.

Comparison of Cell Death Processes

Necrosis: Uncontrolled and passive; results in cell swelling, rupture, and inflammation, typically harmful.
Apoptosis: Programmed and regulated; allows for the removal of damaged cells without inflammation. Initiated either intrinsically (via mitochondrial signals) or extrinsically (via death receptors).
Autophagy: A recycling process during stress, can lead to cell death if excessive. It blurs the line between survival and apoptosis.

General Steps of Apoptosis

Initiation: Intrinsic (damage) or extrinsic (death signals) pathways activate apoptotic mechanisms.
Caspase Activation: Caspase-8 and caspase-9 activate executioner caspases.
Execution Phase: Caspases dismantle cellular components, leading to cell shrinkage and fragmentation.
Apoptotic Bodies Formation: The cell breaks into membrane-bound fragments for phagocytosis.
Phagocytosis: Engulfment of apoptotic bodies by macrophages without inflammation.

Studying That Suits You

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Description

Explore the crucial roles of caspases and apoptotic factors like Bax and Bcl-2 in cell death mechanisms. This quiz examines how their regulation affects apoptosis and cancer development. Test your knowledge on pro- and anti-apoptotic signals that maintain cellular health.