EXAM 2 STUDY SET - CH 13 Flashcards
Na+ — K+ ATPase
Active transport system.
P-Type ATPases.
Forms phosphorylated Asp intermediate.
P-Type ATPases
couple phosphorylation and conformational changes to pump Ca2+ / H+ / Na+ ions, Cu2+ (metal), or phospholipids w/ charged head groups across membranes.
P-Type ATPase Pump has what 2 conformations?
Ion binding site facing into cell.
Ion binding site facing out of cell.
What powers the interconversion of the two conformations of the P-Type ATPase Pump?
ATP hydrolysis
(SERCA) Sarcoplasmic Reticulum Ca2+ ATPase
pumps Ca2+ from muscle cytoplasm to sarcoplasmic reticulum.
SERCA Structure
Single polypeptide chain w/ transmembrane domain - 10 α helices.
SERCA binds?
Ca2+
The cytoplasmic portion of SERCA contains what three domains?
N, P, A
SERCA: N domain
binds ATP
SERCA: P domain
Aspartate residue (Asp 351) accepts phosphate during rxn cycle.
SERCA: A domain
links N and P domains.
Catalytic Transport Cycle: P-Type ATPases
- Bind cytoplasmic Ca.
- ATP binding by N domain.
- Transfer phosphoryl group to Asp in P domain.
- ADP released, structural change, Ca binding site now faces sarcoplasmic reticulum lumen, Ca leaves enzyme.
- Phosphoryl group in P domain hydrolyzed.
- Enzyme changes conf. Ca binding site faces cytoplasm.
P-Type ATPases Fundamental Rxn Mech
Free E release from ATP hydrolysis to drive membrane transport via conf. changes induced via addition / removal of phosphoryl group at key Asp site.
ABC Transporters consist of what domains?
2 ABC domains
2 membrane-spanning domains.
ABC Transporters are characterized by what common domain?
ATP-binding cassette (ABC)
Multi-Drug Resistance protein (MDR)
ATP-dependent Pump.
Extrudes small molecules from cell.
ABC Transporter.
ABC domains
ATP-binding domains
ATP-binding Cassette Domain: Multi-Drug Resistance
Reaction Cycle:
- Channel open to cytoplasm.
- Substrates bind, conf. change in ABC domain.
- ATP binds ABC domains, more structural changes, orient substrate to face outside of cell.
- conf. has reduced affinity for substrate, allows release.
- ATP hydrolysis - resets transporter to initial state.
Lactose Permease
Secondary Transporter / Cotransporter.
Symporter.
Use one [gradient] to power formation of another.
Symporter
Transport molecule against [gradient] by coupling movement w/ another molecule down its [gradient].
Substrates move in same direction.
Antiporter
Use 1 [gradient] to power formation of another.
Transports 2 substrates in opp directions.
Uniporter
Transport 1 substrate / molecule in either direction.
Depends on [difference] across membrane.
Lactose Permease Mech
- Lactose-binding pocket faces outside cell.
- H+ binds, lactose binds.
- Permease everts.
- Lactose leaves permease.
- H+ leaves permease, enters cell.
- Permease everts, cycle complete.
Ion Channels
allow rapid movement of ions across membranes down [gradient].
Depolarization
+ change from resting potential.
Increased permeability to ion.
What happens when the membrane potential is beyond the critical threshold value?
Depolarization.
Nerve impulse / AP gen’d.
Action Potential
Result of K+ and Na+ channels opening / closing in response to changes in membrane potential.
Signals sent along neurons by transient depolarization / repolarization.
Repolarization
Internal charge returns to (-) value.
Typical Membrane Resting Potential
-60mV
neuron interior higher [K+], lower [Na+] than exterior.
K+ Ion Channel Structure
Four subunits - each homologous to one of repeated units in Na+ channel.
4 ion-binding sites.
The Ca+ Channel is homologous to what other channel?
Na+
Na+ Channel
4 repeated regions of similar seq.
Each region:
5 hydrophobic segments.
1 hydrophilic segment.
K+ Ion Channel Function
selectively, rapidly transports K+ along cell membrane.
Why doesn’t the K+ Ion Channel transport larger ions?
too big to enter channel
Why doesn’t the K+ Ion Channel transport smaller ions?
they can’t interact w/ selectivity filter.
E of desolvation can’t be compensated for by interactions w/ selectivity filter.
Voltage-Gated Channels
Na+ and K+ Channels
Change conf. w/ changes in membrane potential.
K+ Channel Segments
S1 - S4 function in voltage gating, “paddle” domains.
Change in membrane potential alter conf. of paddles to open / close channel.
S4 voltage sensor.
Ball and Chain Model
Inactivates K+ Channel.
Ball tethered to channel via polypeptide segment (chain).
Depolarization of the K+ Channel creates a?
binding site for ball, binds, inactivates channel.
Acetylcholine
NT released into synaptic cleft.
Acetylcholine binds to?
channel called acetylcholine receptor.
When acetylcholine is bound to its receptor what happens?
Conf. changes.
Rotate membrane-spinning helices.
Opens K+ and Na+ channel (pore).
Triggers AP.
Acetylcholine Structure
4 subunits
α2βγδ arranged to form pentameric ring.
Nernst Eqn
Equilibrium est’d - driving force of gradient countered by charge repulsion.
membrane potential - equilibrium potential
Action Potential (AP) Generation Mech
- Activate acetylcholine receptor (K+ out, Na+ in).
- membrane potential change activates Na+ Channels.
- Subsequent opening of voltage-gated channels - “ball” of Na+ channel inactivates channel and acetylcholine receptor.
- K+ channels open, membrane potential drops to K+ eq. potential
- K+ channels closed by “ball” segment, membrane potential returns to initial state.
- Events propagated down nerve membrane as AP.
Electrocardiogram: P wave
Atrial myocardium depolarization.
Signals atrial contraction.
Electrocardiogram: QRS Complex
Ventricular depolarization.
Signals ventricular contraction.
Simultaneous atria repolarization.
Electrocardiogram: T wave
Ventricle repolarization.
Precedes ventricular relaxation.
Electrocardiogram: PQ (PR) Interval
Atria contract, relax, ventricles contract.
.16 sec
Electrocardiogram: QT Interval
Ventricles contract, begin to relax.
.36 sec
Aquaporin
Allow rapid, specific water movement across membranes.
Increase permeability of some membranes to water.
Aquaporin Structure
Hydrophilic residues line water channel.
Ligand-Activated Channel
acetylcholine receptor
Where does aquaporin exist?
Plasma membranes of kidneys. Liver. Eyes. GI Organs. Lungs. Glands.
Diffusion
Movement of molecules from region of [high] to [low].
Down [gradient]
Gap Junction
Cell-to-cell channels.
Passage of materials btw adj. cells.
Intercellular communication.
Polar molecules <1kDa can pass.
Gap Junction Structure
12 molecules of connexin 6 hexagonally arranged - form connexon. Connexon from adj. cells form gap juncton. Traverse 2 membranes. Cytoplasm-to-cytoplasm communication.
