cell bio 2d
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what are the stages of autophagy?
- merging with lysosome
- resulting residual body
what is the function of ESCRT?
bring receptors together to concentrate them and then MVB's fuse with lysosome to rid receptors (reuse them)
how does cell downregulate signal?
by bringing it in and sending them to degradation pathway
how does the secretory system work?
- cargo proteins are translocated to the ER lumen
- in the ER, cargo fold and inserted into VTCs
- VTCs transport cargo to Golgi, where their oligosaccharide and polypeptide chains are processed
- motors are translocated
what's the signal for proteosome?
multiple ubiquitin attached
how does ubiquitin attach to E1?
describe the process of ubiquitin conjugation mechanism
- using ATP, ubiquitin attached to E1, ubiquitin-acitivating enzyme
- E2 attaches to ubiquitin and recognizes protein for degradation,
- coupled to E3 (protein ligase) binds to prtein to be degraded, and transfers ubiquitin from E2 to protein using ATP
- proteosome chews protein up into aa and small peptides to be recycled
how do cells respond to their environment?
each cell expresses a genetically programmed repertoire of receptors, transuction hardware and effector system
how does signal transduction affect cells?
change in gene expression, cell shape, cell movement, cell metabolism
why do most stimuli react on receptors at PM?
they cannot penetrate PM, some light, steroid hormones, gases can penetrate PM,
how are receptors inactivated?
negative feedback, inhibitory ligand binding and phosphorylation of receptor
what are the two classes of signaling molecules?
- large requiring cell surface receptors (growth factors, cell cell interactions)
- small or hydrophobic and able to cross PM
signals lead to both short term and long term effect; what are the short and long term effects?
- short term: change in cell activity in cytoplasm (altering protein function)
- long term: altering gene expression (can be affected by the same signaling molecule)
what is the general pathway of cell receptors?
- signal transduction (converts mechanical or chemical mechanism to specific cellular response)
- feedback loops
what is the effector of seven-helix?
trimeric G protein
what is the effector of receptor tyrosine kinase and cytokine?
what is the effector of receptro guanylyl cyclase?
how does receptors transfer signal?
by conformational change or clustering to activate each other
what are the three major classes of cell surface receptors?
- ion channel linked receptors
- G-protein linked receptors
- enzyme linked receptors
what are the characteristics of seven helix receptor?
- use trimeric G-proteins to relay signal
- largest family of receptors; very ancient
- drug targets
- structurally similar to rhodopsin
- olfactory neurons and sight associated with this kind of receptors
where does rod photoreceptors process light signals?
in their outer segments
how is rhodopsin activated?
light binding to retinal will activate transducin, a heterotrimeric G protein
what promotes the exchange of GTP for GDP, activating the G protein?
what is the role of alpha and gamma subunits of trimeric g protein?
- alpha and gamma both have tails anchored on PM, alpha is regulated by GAP and GEF (activate and inactivate it)
- alpha and beta subunits are activated by GTP binding
how is the G protein coupled receptors activated?
- ligand binds to receptor (changes in conformation)
- G-protein binds to G protein coupled receptor, which exchange GTP for GDP (subunits separate)
what activates ATP bound protein?
- ATP (protein kinase turns it on)
- protein phosphatase dephosphorylates turns it off
how to activate and inactivate signaling by GTP binding?
GTP bound is on, GTP hydrolysis is off
what are the molecular switches that activate and inactivate monomeric proteins?
- GAPs induces hydrolysis of GTP (inactivating)
- GEFs are activating
describe signaling amplification in the retina
- one rhodopsin molecule absorbs one photon
- G protein (transducin) activated
- cyclic GMP phosphodiesterase activated
- Na channels close (change in membrane potential
- signal to brain
what terminates G protein activation and causes reassociation of trimer?
GTPase of alpha subunit
what are the different receptor signaling types?
- endocrine (through blood stream)
- paracrine (close contact with another cell)
- contact dependent (regulating self)
- snaptic (neuronal )
what are the signaling molecules?
- ligands (change shape and activity)
- small molecules (lipophilic-intracellular receptors in cytosol or nucleus which bind to transcription factors)
can steroid hormones cross membranes?
yes, binds directly to nuclear receptors, influencing transcription, all made from cholesterol
what are the different types of steroid hormones?
what are the different growth factor receptors?
- receptor tyrosine kinases
- cytokine receptors
- receptor serine/threonine kinases
what does ligand binding do in receptor tyrosine kinases?
induces dimerization and activation
EGF binding does what to an autoinhibited monomer?
ligand binding opens extracellular domains
what is a SH2 protein?
- Grb2 is an example
- bind to P-tyr motif in receptor, which binds other proteins
what is the role of Ras (G protein)
- activates MAP kinase cascade
- GDPases as molecular switches
- RasGAP hydrolyze GTP to GDP
- only active when linked to PM
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