Block 2 - Intro to Cell Communication Flashcards
What are the 4 ways cells can communicate change?
contact dependent - signal molecule in one cell contacts receptor on another cell
paracrine - cell to signaling cell to target cell
synaptic - one cell contacts another cell via a synapse
endocrine - endocrine cell releases a hormone into the bloodstream that reaches a receptor on a target cell
Certain specialized receptor cells respond to —– stimuli
external
Cell communication often involves —– signals
chemical
Chemicals that are produced in one cell that work over a distance to produce a response in a second cell are called…
hormones
Peptide and protein signaling molecules can’t —– so they require —–
can’t cross the plasma membrane so they require a receptor on the cell’s surface
True or False: only a single stimuli or receptor links to a given signaling pathway
False - many can link to the same pathway
When a chemical signal reaches a cell, the response is often caused by…
- speeding up/slowing down a biochemical reaction
- increase/decrease a protein by altering transcription or translation
- change the activity of a protein by phosphorylation/dephosphorylation (post-translational modification)
- change the location of a protein
- start/stop the release of a secreted product
What are the three classes of plasma membrane receptors?
ion channel linked receptors
g protein coupled receptors
enzyme linked receptors
All plasma membrane receptors are…
integral membrane proteins
What are GPCRs?
- g protein coupled receptors
- activate a class of GTP binding proteins (G proteins) which are molecular switches that turn on while bound to GTP and turn off by hydrolysis of GTP to GDP
What are GTP and GDP?
guanosine triphosphate
guanosine diphosphate
GPCR’s have —- transmembrane spans and associate with a —unit G protein
7 transmembrane spans
3 unit G protein
When a ligand binds to the GPCR, what happens?
- GTP exchanges for GDP on the G protein
- alpha subunit dissociates from the complex and activates signaling pathways that bring about a cell response
True or False: the dissociated alpha subunit of a G protein always activates the same pathway
False - they are associated with different receptors and can activate different signaling pathways
G proteins can…
- regulate ion channels
- activate adenylate cyclase (increasing intracellular cyclic AMP)
- activate Phospholipase C (increasing intracellular IP3 and DAG)
Increasing cAMP can lead to…
protein phosphorylation
- activates protein kinase A which leads to protein phosphorylation and many different types of cell response
Protein Kinase A plays a role in phosphorylation, but also…
interacts with cAMP response element CREB to activate transcription (so it activates a transcription factor)
Many stimuli rely on —– signaling to “get their messages through”
cAMP signaling
What happens after GPCR signaling activates phospholipase C?
- IP3 is released into the cytosol
- Ca++ release from the ER is stimulated
- elevated Ca++ activates calcium-dependent protein kinases and phosphatases that alter the activity of target proteins
AND
- DAG is produced and remains in the membrane (because it is hydrophobic)
- DAG activates members of the protein kinase C family
Most signaling molecules can’t —- so their receptors…
can’t pass through the cell membrane, so their receptors are in the cell membrane
Some small hydrophobic signal molecules like steroids can —– so their receptors…..
can diffuse directly in to the cell cytoplasm so their receptors are cytoplasmic or nuclear
True or False: a stimuli can only act at one site
False - certain stimuli can act at more than one site and have more than one response/effect
Signaling pathways allow the response to….
be amplified, and cause a pattern of changes involving several different reponses
Although cells have many ways to cause a reponse, it is also important that they can…
terminate a response, diminish responsiveness, and prevent overstimulation
What are the 5 ways a cell can terminate response?
receptor sequestration
receptor down regulation
receptor inactivation
signaling protein inactivation
production of an inhibitory protein
What are Arrestins and how do they work?
- cytosolic proteins that recognize agonist-activated receptors and bind to them
- makes the receptor inaccessible for G proteins
- receptor is targeted for internalization by clathrin-coated pits and then as vesicles, where they are either recycled or sent to be degraded
