Why do cells need extracellular signals?
A: They are required for cells to survive, grow, and divide.
Where do extracellular signals come from?
Other cells; mostly soluble proteins that are secreted or cell-surface–bound
What do most extracellular signals do?
Stimulate a process, but some inhibit.
Three positive signal types
Mitogens, growth factors, survival factors.
What are mitogens?
Secreted proteins that bind cell-surface receptors and release molecular “brakes” that block entry into S phase.
What do mitogens push the cell through?
The start transition into cell division.
Example: Platelet-derived growth factor (PDGF)?
Example: Hepatocyte growth factor?
Released by platelets at a wound; binds receptor tyrosine kinase; causes nearby cells to proliferate to heal. pdgf both mutigen and growth factor.
Stimulates liver cells to proliferate after injury.
How do growth factors work?
Promote macromolecule synthesis; inhibit macromolecule breakdown
Do growth factors depend on the cell cycle control system?
No, many cells grow even after terminal differentiation.
How is PDGF also a growth factor
It stimulates growth and ensures cells stay the correct size when dividing.
What is apoptosis
Programmed, neat cell death that prevents damage to neighbours
Why is apoptosis important?
Controls cell numbers; shapes development; maintains adult tissues.
apoptosis example in development?
Removing webbing between toes; removing tadpole tail.
eg 2 if liver enlarges (e.g., due to phenobarbital), apoptosis restores normal size
process of apoptosis: What are blebs?
cannot just burst…
Irregular bulges on an apoptotic cell.
Cell shrinks; cytoskeleton collapses; nuclear envelope breaks apart; DNA fragments
What are caspases?
Proteases made as inactive precursors, activated during apoptosis
Two types of caspases
Initiator caspases and executioner caspases.
initiator= activate executioner caspases
executioner= Break down proteins; e.g., destroy lamin proteins in nuclear lamina to allow DNA breakdown.
What do Bcl2 proteins control
Activation of caspases, can promote or inhibit cell death.
What do Bax and Bak do
Activated by DNA damage; promote apoptosis by releasing cytochrome c from mitochondria.
What does Bcl2 do?
Inhibits apoptosis by preventing Bax and Bak from releasing cytochrome c.
What happens when cytochrome c is released?
It triggers cell death.
What complex does cytochrome come form?
The apoptosome, a seven-armed structure.
function of apoptosome?
Activates initiator caspase → starts caspase cascade.
What is a death receptor?
Cell-surface receptor that receives apoptotic signals.
Example: Fas receptor?
What does Fas activation cause?
Activated by Fas ligand on killer lymphocytes or natural killer cells
Formation of a death-inducing signalling complex containing initiator caspase → apoptosis.
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CB: intro to cellbio11
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chem conversions6
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ch 1 med plants29
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cb: chemical components of cells17
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ch2 med plants: history of etheogens17
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Ch3 medicinal: 2 plant biochem6
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ch4 med plants: poisonous fungi and plants21
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unit 3 cb: bioenergetics20
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mod 2: vocab chem29
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u4 cellb: protein structure41
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u5 med plants: deterrents from fungi & plants55
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u6 med plants: cancer treatments15
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u7 med: adaptogens/opto19
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u5 cellb: dna and chromosome (midterm 2)30
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med plant u8: heart and circulatory system20
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med plants unit 90
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u6 cellbio: dna replication and repair38
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u7 cellb: dna/protein31
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cellb u8:gene expression32
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cellb u9 genetic ev23
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cellb u10: memb structure27
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cellb u11 memb transport31
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u11 medp:central N sys33
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U12med: stimulants3
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cellb u12 cell signalling31
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cellb u13: mitochondria & energy34
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cellb u14 cell cycle24
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Cellb u1529
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cellb u1623
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cellbio u1720
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cellb u1815
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cellb u1920
