Lecture 16: membrane transport and signaling Flashcards
simple passive transport
down gradient and is energy independent [linear]
facilitated transport
involves a carrier but can be passive or active [hyperbolic]
passive vs active transport
- passive = both move down their gradients
- active = at least one moves against [up] its gradient
gap junctions are ____ transport
facilitated passive transport
what causes the channel to open/ close in a gap junction?
Ca causes conformational change [> 10^-5 = closed]
kinetics of gap junction
linear kinetics
gramicidin A [channel lonophore]
- dimer of left-handed helices “end-to-end”
- antibiotic of bacterium that collapses ion gradient between cytoplasm and the extracellular environment
valinomycin [carrier ionophore] uses ____ transport and coordinated with ___ by _____
- facilitated passive transport
- coordinates K+
- hydrophobic R-groups = can carry things through the membrane [like a cage]
sodium-glucose transporter is
secondary active symport
sodium-glucose transporter wants ____
wants glucose from outside to inside [low to high] = unfavorable so gets energy from Na going down its gradient [favorable]
signal transduction involves an _____ acting as a receptor [R] ; binds ____ at cell surface
integral membrane protein; binds ligand
signal transduction process
- recognition = receptor binds only its specific ligand
- signal transmission = binding may change membrane permeability; allow association of other proteins to R; causes internilization
- **can have signal amplification
beta-A binds to ____ which initiates
binds to hormone epinephrine which initiates sequence of events that amplifies inside cell
how does adenylate cyclase get activated in Adrenergic system?
beta receptor reacts with/ activates G-protein = becomes GTP and activates AC
AC converts AMP to cAMP by ___
removing 2 phosphate groups
what converts cAMP to AMP?
phosphodiesterase
2nd messenger for activity in adrenergic system
cyclic AMP [cAMP]
effect of caffeine in adrenergic system
inhibits the enzyme that deactivates cAMP = more signaling activity
amplification: most steps in the pathway are ____; 1 molecule at step 1 produces _____
- most steps in pathway are catalytic
- 1 molecule at step 1 produces many downstream
example of desensitization in Adrenergic system caused by what
- intrinsic GTPase activity of Gα-GTP complex
- phosphodiesterase converts cAMP to AMP = turns off signal cascade
lateral diffusion; prefers what type of fluidity?
- G-proteins must move within membrane to interact with the 7-transmembrane receptors
- anything that affects fluidity will also effect efficiency of G-protein
- prefers more fluid
