Test 2 Lecture 28-29 Flashcards
Membrane proteins facilitate the transport of ions as well as drugs and proteins.___,
a family of cell adhesion receptors
Integrins
The concentration gradients of various ions (Na+, K+, Ca2+, etc.) set up an ____ across the plasma membrane (about -60 to -75mVolts) that are
critically important for membrane function.
electro
potential gradient
The Na+/K+ pump pumps 3 Na+ outside in exchange for 2K+ inside (against the gradient), thus generating an ____ across plasma membrane.
electrochemical gradient
The ion channels (Na+, K+, Ca2+, etc) are regulated membrane pores which open for
less than a millisecond and transport <107 ions during this short time. They are regulated
by changing ____
electrical potential or ligands.
The inactive state of the ion channels allows the action potential to progress in only ____ and thus lead the signal to the other end of nerve axons.
one
direction
The action of ionic channels and pumps are important for propagating ___
and pathogen mediated signaling.
sensory signaling
uniport system
can only go one way
symport transport system
needs 2 different molecules to bind and then can go through
antiport transport system
needs molecule at both sides and switches
transport that goes with gradient
example
passive
glucose will travel through glucose permease (glucose transporter)- α- helical transmembrane segments form a central aqueous cavity for transporting glucose.
Cells have a transmembrane electrical potential of about ___ mVolts. This electrical gradient is built by ___ transport
-60 to -75
active
Mammalian cells have more of which ions on the inside and outside
inside:
K
outside
sodium, Cl, bicarbinate, Mg, Ca
ion gradients help with
sodium/ potassium pump
general
3 sodium out
2 potassium in
one ATP used: one ADP formed
Na/K pump confirmations
E1: 3 Na+ attach, ATP is used and P is attached changing shape and releasing Na into ECM
E2: 2 K attach, P is kicked off and changes shape and K is released into inside of cell
3 Na out: 2 K in
The Na+/K+ pump is driven by the ___ of ATP, and it contains an ATPase activity at its cytoplasmic domain.
hydrolysis
The Na+/K+ pump is electrogenic, and is responsible for setting and maintaining the ___ in almost all cell types
membrane potential
The membrane potential set up by the Na/K pump is a form of stored (or usable) energy, which is utilized for pumping other ions and nutrients across the plasma membranes. The membrane potential is also essential for the transmittal of nerve impulse in the form of ____, from the brain to neuromuscular junctions for muscle contraction.
action potential
Digitalis and other cardiotonic steroids, that are popularly used to treat congestive heart
failure, inhibit the Na/K pump by binding to its ____. Inhibiting the pump for a limited duration reduces the ___ gradient across the membrane, which indirectly increases the intracellular ___ level, thus inducing the cardiac muscle contraction.
extracellular side.
Na+
Na+
how do digitalis work
bind to outside of Na/K pump (blocks dephosphorylation of E2)
prevents Na from being pumped out, Na inside cell increases and cause cardiac muscle contraction
Steps of Na/K pump
- pump is either in E1 (Na) or E2 (K)
- E1: binds 3 Na+ ions from the cytosolic side, phosphorylation of the protein at an Asp residue facing the cytosolic side
- Phosphorylation induces a conformational shift : pump opens to the extracellular side to release the Na+ ions.
- E2 state, 2 K+ ions bine from the extracellular side
- Binding of 2 K+ ions induces dephosphorylation (at the Asp residue), conformational shift and release the 2 K+ ions inside the cell.
3 ways to Na back into cell
Na/K pumps: pump 3 Na out (+ outside, - inside)
Na/Ca antiport pump will bring Na into cell
Na/H antiport pump will bring Na into cell
Na/glucose symport pump will bring Na and glucose into cell
Ion channels are mostly passive and function as a ___
pore.
Ion channels opens for less than a ___ during which time large amounts (up to 107) ions gush in or out along the concentration gradient.
m-second
Ion channel opening is either regulated by change in the ____(voltage gated) or by specific neurotransmitters or other ligands (such as ___) binding to channels which essentially function as receptor coupled pores (ligand gated).
membrane potential
acetyl choline and capsaicin
Voltage gated Na+ Channel are regulated by changing ___
membrane potential
___ region of neurons are rich in voltage gated Na+ channels that are activated by change in the ionic equilibrium across the membrane caused by incoming ___
axonal
action potential.
tetrodotoxin
inhibits sodium channel
puffer fish
how does acetylcholine channel pore work
Lucine sits in pore
acetylchloline binds : helix rotates and serine (smaller, hydrophilic) in center: opens pore
pore will automatically close
ligand gated channel
explain ball and chain
membrane + outside
( pore closed)
membrane - outside (depolarized)
(pore opens), H2N ball moves to block hole (inactivated)
membrane returns to + (pore closes and ball moves)
Acetyl choline mediated opening of ligand gated ____. Post synaptic membrane of neurons and nero-muscular junctions are rich in acetyl choline gated Na+ channels.
Na+ channel.
Acetyl choline receptor Na+ channel is ___ gated channel
ligand
“the ball and chain” mechanism helps prevent excessive ___ both inside and outside the cell during the 10-20 m-seconds needed to reestablish the membrane potential that brings the channel to steady state level.
ion movement
Post synaptic membrane of neurons and nero-muscular junctions are rich in ____
acetyl choline gated Na+ channels.
explain action potential
Na open and Na comes into the nerve, changing the internal charge to + (depolarization)
at peak (+30) Na close, K open (repolarization)
K will leave nerve, this will make internal charge -, K channels close, but are slow and goes to far (refractory period)
resting potential goes back to normal through Na/K pump
absolute refractory period
prevents another action potential from coming too early
prevents going backwards
at the end of a neuron, change in internal to + will cause opening of Ca channels and Ca will ___ cell. This will cause the ___ of secretory vesicles containing acetylcholine
go into
release
how does nerve impulse move across neuronal junctions
1) activation voltage gated Ca2+, Ca comes in and induces docking of acetylcholine vesicles and release of acetylcholine into the synaptic cleft.
2) acetylcholine mediated activation of Na+
Na channel on other neuron will bind to acetylcholine, open up Na will come in and action potential will start
Sense of burning heat and hot food (___) involve the action of an unusual Na+/Ca2+ channel.
capsaicin)
how does VRI work?
vanilloid receptor Type I (VRI)
activated by binding of capsaicin
channel opens , allowing influx of Ca2+ and Na+ ions. The influx depolarizes neuronal pain fibers, initiating a nerve impulse through the dorsal root ganglion (DRG) to the brain.
why you feel hot when you eat chilli peppers.
explain how botulinum toxin can be used
Botulinum toxin = muscle paralysis.
produced by the bacterium Clostridium botulinum.
It is polypeptide consisting of a light chain and a heavy chain bridged by a single disulfide bond.
BOT used to fix facial wrinkles, and prevent sweating, help headaches
how does botulinum work?
binds to neural end plate and prevents binding of acetylcholine vesicles
botulinum binds to the presynaptic terminal and enters by endocytosis.
The disulfide bond linking the two botulinum-toxin chains is broken, and the light chain is translocated out of the endocytotic vesicle into the cytoplasm.
Botulinum toxins A, C, and E cleave the 25-kd synaptosomal-associated protein SNAP-25; types B, D, F, and G cleave a synaptobrevin vesicle- associated membrane protein (VAMP); and type C cleaves syntaxin.
acetylcholine cannot be released, and the muscle is paralyzed
Tight junctions seal adjacent epithelial cells just beneath their ____ thus preventing passage of molecules and ions from the luminal side to the basolateral side of the epithelial layer.
apical surface
tight junctions block the movement of ____ between the apical and basolateral surfaces thus help maintain the specialized functions of different cell regions.
integral membrane proteins
___ junctions provide strong mechanical attachments between adjacent cells.
Adherence
Adherence junctions can:
hold cardiac cells together as the heart expands and contracts
hold epithelial cells together
responsible for contact inhibition during cell growth.
Adherens junctions are built from ____ — transmembrane proteins whose extracellular segments bind to each other and whose intracellular segments bind to ___ which are connected to ___ filaments.
cadherins
catenins
actin
Loss of functioning adherens junctions may also lead to ___
tumor metastasis.
Gap junctions
intercellular channels: 1.5–2 nm in diameter.
free passage of ions and small molecules
They are constructed from 4 (sometimes 6) copies of one of a family of a transmembrane proteins called connexins.
Because ions can flow through them, gap junctions permit changes in membrane potential to pass from cell to cell.
Because ions can flow through them, ___ permit changes in membrane potential to pass from cell to cell.
gap junctions
Desmosomes are localized patches that hold two cells tightly together. They are common in epithelia (e.g., the skin). Desmosomes are attached to ___ of keratin in the cytoplasm.
intermediate filaments
___ are localized patches that hold two cells tightly together, common in epithelia
Desmosomes
Role of adherence junctions and cytoskeleton
Integrin mediated transmission of Cell signaling from extracellular matrix to the cell nucleus.
integrin attach to ECM and FAK proteins
FAK attaches to FA and that sends signal through cytoskeletal fibers into nucleus
focal adhesion
vinculin
pacillin
talin
