Cell Stress Part 2 Flashcards

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1
Q

What do Lysosomes normally do ?

A

Lysosomes normally supply extracellular nutrients to cells

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2
Q

Lysosomes Harbour what ?

A

Lysosomes harbour many enzymes that degrade macromolecules at acidic pH

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3
Q

What do Lysosomes digest ?

A

Lysosomes also digest intracellular contents acquired by autophagy This allows recycling of macromolecular building blocks during starvation Autophagy from Greek: “self-eating”

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4
Q

Autophagy ?

A

Autophagy is initiated by engulfing damaged organelles and cytosol with a double membrane derived from the ER

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5
Q

Functions of autophagy

A

Normal “housekeeping”  Increased to allow recycling of macromolecules under starvation conditions  Responses to viral and bacterial infections

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6
Q

Cell Death

A

Necrosis

Nutrient starvation or extensive chemical damage  Cells run out of energy (ATP) 

Unable to maintain ion gradients 

Osmotic influx of water swells, bursts cells

 Cytosolic contents released; inflammation is triggered in multicellular organisms

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7
Q

Cell Death

A

Apoptosis

Regulated cell death
 Removal of unwanted cells 

Surplus during development (external cues) 

Too stressed, DNA too damaged (internal state) 

Dead cells must be cleared, without inflammation

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8
Q

Forms of Cell dEATH

A

Two major forms: necrosis and apoptosis 

Necrosis is passive, resulting from loss of metabolic control 

Any cell may suffer necrosis 

Inflammation results from release of cytoplasm

Apoptosis is death regulated in multicellular organisms by internal state or external cues

 Removes unwanted cells without inflammation

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9
Q

Apoptosis

A

Specific external stimuli (engagement of “death receptors”), or sensing of internal state (DNA damage, mitochondrial dysfunction) 

A molecular “decision” is made, which activates caspases 

Caspases dismantle the cell without disrupting the membrane 

In whole organisms, the cell remnants can be taken up by nearby cells without inflammation or loss of tissue integrity 

Removal of “distressed” cells with minimal damage to the organism (via mitochondrial pathway) 

Or removal of cells during normal development

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10
Q

Overall Summary

A

Cells can be stressed by various factors, which damage macromolecules or remove nutrients 

Most damaged cell constituents may be degraded and replaced; DNA must be repaired

 Background damage is omnipresent and inescapable 

Stress response mechanisms  are in place all the time (“constitutive”), and  are induced when cells are stressed (e.g., unfolded protein response, autophagy) or especially vulnerable (e.g., to DNA damage in mitosis) 

Acutely starved or energy-deprived cells die by necrosis (in multicellular organisms, this causes inflammation)

 In multicellular organisms, unwanted cells may die by apoptosis

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