Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE...
Transcript of Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE...
![Page 1: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/1.jpg)
Membrane channels and pumps
Stryer ch 13
![Page 2: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/2.jpg)
Concentration & potential differences across cell membranes
![Page 3: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/3.jpg)
MEMBRANE TRANSPORT SYSTEMS
Regulate the cellular volume
Control the transfer of metabolites across membranes
Maintain ionic and molecular gradients across membranes
DIFFERENT TYPES OF TRANSPORT SYSTEMS
Passive diffusion e.g, hydrophobic molecules
Facilitated diffusion by channels e.g. transfer of
metabolites and ions
Active transport
![Page 4: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/4.jpg)
µ’’
!’’, c’’
!’, c’
µ’
The thermodynamics of transport across membranes
µ’ = µ0 + RT ln c’ + zF!’
µ’’ = µ0 + RT ln c’’ + zF!’’
"G = µ’’ - µ’ = RT ln c’’/c’ + zF (!’’ - !’)
"G > 0 active transport
"G < 0 passive transport
![Page 5: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/5.jpg)
[Na+] [K+]
Outside cell 140 mM 5 mM
Inside cell 10 mM 100 mM
"G = RT ln c’’/c’ + zF "!
Transport of 3 mol Na+ from inside to outside of a cell at a
transmembrane potential of 70 mV
"G = 3 RT ln [Na+]out / [Na+]in + 3 F (!out - !in)
= (20.5 + 20.5) kJ = 41 kJ
Transport of 2 mol K+ from outside to inside of a cell
"G = 2 RT ln [K+]in / [K+]out + 2 F (!in - !out)
= (15.5 - 13.5) kJ = 2 kJ
At physiological conditions ATP ADP + P "G = -60 kJ
![Page 6: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/6.jpg)
Conditions required for a protein to work as a
transmembrane pump
• Protein must contain binding sites to fix substances
which should be transported
• Protein must exist in two conformations
• Binding sites must have different affinities in the two
conformations
![Page 7: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/7.jpg)
Free energy changes for transport processes
"G = RT ln c’’/c’ + zF "!
![Page 8: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/8.jpg)
Structure of the Ca2+ ATPase
![Page 9: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/9.jpg)
The transport mechanism of the Ca2+ ATPase
![Page 10: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/10.jpg)
The transport mechanism of the Ca2+ ATPase
![Page 11: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/11.jpg)
The transport mechanism
of the Na+- K+ ATPase
[Na+] [K+]
Outside cell 140 mM 5 mM
Inside cell 10 mM 100 mM
![Page 12: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/12.jpg)
Some co-transport systems
Molecule Ion gradient Organism
transported or tissue
Glucose Na+ Intestine, kidney
Amino acids Na+ Mouse tumor cells
Lactose H+ E. coli
![Page 13: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/13.jpg)
![Page 14: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/14.jpg)
Scheme of active transport by Lactose Permease
![Page 15: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/15.jpg)
Scheme of active transport by Lactose Permease
![Page 16: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/16.jpg)
X-ray structure of Lactose Permease
![Page 17: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/17.jpg)
Structural changes of Lactose Permease during active transport
![Page 18: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/18.jpg)
![Page 19: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/19.jpg)
Ion Channels
![Page 20: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/20.jpg)
Morphology of two types of mammalian neurons
![Page 21: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/21.jpg)
![Page 22: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/22.jpg)
Transport rate of ions across membranes
Pumps ca 1000 ions/second
Channels 106 - 107 ions/second
![Page 23: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/23.jpg)
Some properties of ion channels
1. Ion channels can be highly selective
2. They exist in an open and a closed state
3. The transition between open / closed stae is regulated
4. Open states often spontaneously convert to inactivated form
![Page 24: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/24.jpg)
Schematic representation of a synapse
Voltage-gated ion channels
Ligand-gated ion channels
![Page 25: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/25.jpg)
Synaptic vesicles: 104 Ach
300 vesicles release Ach
[Ach] 10 nM > 500 µM in ms
Ach binds to postsynaptic
membrane
![Page 26: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/26.jpg)
![Page 27: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/27.jpg)
Membrane depolarization
![Page 28: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/28.jpg)
Patch clamp technologyE Neher & B Sakmann 1976
![Page 29: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/29.jpg)
Patch clamp recording of acetylcholine receptor channel
![Page 30: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/30.jpg)
+
Electrical eel: source of AchR
Torpedo Marmorata
![Page 31: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/31.jpg)
![Page 32: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/32.jpg)
Action potentials are mediated by transient changes of Na+
and K+ permeabilities
![Page 33: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/33.jpg)
Opening of
AchR channel
![Page 34: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/34.jpg)
Opening of K+ channels &
restoration of resting potential
![Page 35: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/35.jpg)
![Page 36: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/36.jpg)
Topology of Na+ channel
![Page 37: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/37.jpg)
Sequence relationships of ion channels
![Page 38: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/38.jpg)
Structure of potassium channel
![Page 39: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/39.jpg)
Details of structure of
potassium channel
![Page 40: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/40.jpg)
Considerations on the
energy of ion selectivity
![Page 41: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/41.jpg)
![Page 42: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/42.jpg)
![Page 43: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/43.jpg)
Summary
Specific channels rapidly transport ions across membranes
Ions flow down their concentration gradient
Responsible for nerve impulses
- Specificity for certain ions
- Existence of open & closed states
- Regulated by ligands or trans-membrane potential
![Page 44: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/44.jpg)
![Page 45: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/45.jpg)
![Page 46: Stryer ch 13 · Stryer ch 13. Concentration & potential differences across cell membranes. MEMBRANE TRANSPORT SYSTEMS Regulate the cellular volume Control the transfer of metabolites](https://reader030.fdocuments.us/reader030/viewer/2022040501/5e226899366058309a517fc1/html5/thumbnails/46.jpg)