membrane transport1 not responsible for: nernst equation, other than to know what it’s used for....
TRANSCRIPT
Membrane Transport 1
Not responsible for:Nernst Equation, other than to know what it’s used for.
Chapter 12 Membrane Transport
Questions in this chapter you should be able to answer:Chapter 12: 2-14, 16, 17, 19, 20, 21A, B, 22, 23
Membrane Transport 2
To what are membranes permeable?
Where are membrane transport proteins found?
Aquaporin transporters can facilitate H2O transport in some cells
Membrane Transport 3
How do we describe the properties of membrane transport proteins?
1. Symmetry of transport
2. Mechanism of transport
Transport symmetry
Membrane Transport 4
3. Energy requirements
What defines ‘active’transport?
What potential sources of energy for active transport?
Concentration gradients
ATP
Light
Electrical attraction
Membrane Transport 5
What is “membrane potential”
What ions are commonly involved?-- Na+, K+, fixed ions
Outside Insidelow [ K+] High [K+]High [ Na+] Low [Na+]
Read text of Figure 12-21pg 399
Movement of K+ through the‘K Leak Channel’ establishes the cell’s ‘resting potential’
-- concentration gradient-- electrical attraction-- -20 to -200 mA
inside
outside
Membrane Transport 6
What are examples of transport coupled to electrochemical gradients?
Na+ gradientsH+ gradients
called 2O active transport
What is an electrochemical gradient?
concentration gradient+
membrane potential
ECG can drive or impede transport
Membrane Transport 7
What are the properties and functions of the Na-pump (Na/K pump)-- 3 Na+ out for 2 K+ in
What are its…
Symmetry?
Mechanism?
Energy requirement?
What are its functions?
maintenance of tonicity
maintenance of the Na+ gradient
Question 12-2, pg 395Na/K pump
Membrane Transport 8
How can cells alter membrane potentialand respond to its changes?-- ‘gated’ ion channels
Nerve impulse; muscle contraction-- Voltage-gated and ligand-gated
Sense of hearing;Plant movements-- Mechanically-gate channels
Dirurnal cycling;Phototaxis-- Light-gated channels
Tick and Sick-4 9
At sensory cells, opening of ion transporters creates nerve impulse
Stimulus opens Na+ channels e.g., stereocilia of inner ear
Na+ rushes into cell
Changes membrane potential
Tick and Sick-4 10
Nerve impulses travel from sensory neurons
motor neurons
Membrane Transport 11
What is a nerve impulse??
A nerve impulse is an altered membrane potential
= “action potential”
Wave-like movement
Electrodes can show movementof the action potential
Membrane Transport 12
The cellular foundation of “neurobiology” -- the giant neuron of the squid
Used to study factors that affect action potential
-- e.g., effect of [Na+]
Membrane Transport 13
An action potential can be studied experimentally?
“Voltage clamping” can be used to manipulate membrane potential
-- & study effects
Stimulating electrode:-- alters membrane potential
Measuring electrode:-- measures current (ion) flow
Voltage-gated ion gates respond
Threshold potential
Refractory period
Measure current Set (‘clamp’)
membrane potential
Schematic of Voltage Clamp Device
axon
Stim
ulat
ing
volta
geM
embr
ane
Pot
entia
l (m
V)
Tick and Sick-4 14
Nerve impulse ion flow
During propagation of Action Potential, waves of Na+ and K+ ions move back and forth across membrane
Due to opening and closing of ion channels-- why does A.P. move??
Membrane Transport 15
How can the properties of different ion channels be studied?
Patch Clamping
Can measure current through a single channel
Question 12-4, p 405
Tick and Sick-4 16
K+ then flows out of cell restores Resting
Potential
Na+ flows into cell Action Potential
Action Potential triggers opening and closing of“voltage-gated Na+ channels” “voltage-gated K+ channels”
Membrane Transport 17
Why do the Na+ and K+ channels open and close at different times?-- Membrane potential alters their state
voltage-gated Na+ channels-- 3 states
voltage-gated K+ channels-- 2 states
closed open closedState of K+Channels
State of Na+Channels
The “wave”
Tick and Sick-4 18
Flow of Na+ ions opens Voltage-gated Na+ channels
voltage-gated Na+ channels
voltage-gated K+ channels
Propagateimpulse
RestoreResting potential
ActionPotential
Tick and Sick-4 19
What happens when nerve impulse reaches the end of axon?
Neurons pass signals
at a synapse
Membrane Transport 20
What happens when an action potential reaches the synaptic complex?
Presynaptic membrane Post-synaptic membrane Voltage-gated Ca++ channels Ligand-gated Na+ channels Exocytosis of vesicles Voltage gated Na+ channels
Synaptic Signaling
Tick and Sick-4 21
“Neuro transmitters” are the chemical signal passed from cell-to-cell
Common examples-- Dopamine-- Serotonin-- Acetylcholine
Some are inhibitory-- GABA
Bind to receptors-- Ligand-gated Na+ Channels
Tick and Sick-4 22
Excitatory Neurotransmitters open Na+ channels -- Na+ flows through open channels
-- alters membrane potential-- create action potential in next cell
Synaptic Signaling
Tick and Sick-4 23
Cell process both excitatory and inhibitory signals
-- may signal or not
Membrane Transport 24
Adapted form question 19-19.
The inside of endosomes is acidic, which is achieved by the presence of a H+ pump in the endosome membrane. The endosome membrane also contains a transporter which pumps Cl- into the endosome. If a mutation eliminates the Cl- pump, acidification of the endosome is impaired.
A, Draw a diagram of the endosome showing the two transporters and the movement of ions.
B. Why does a mutation to the Cl- pump impair endosome acidification?
C. Could a Ca++ pump substitute for the Cl- pump? Why or why not?