FOM 1.4.2 Flashcards
Membrane is permeable to…
○ Gases: O2, CO2 ○ Small uncharged: EtOH somewhat permeable to water
Membrane is NOT permeable to..
○ Ions: H+, Na+, K+, Cl- ○ Large, uncharged: glucose ○ Large, charged: amino acids, peptides, nucleotides, phosphate ions
describe the effects of osmotic pressure and water transport
○ Hypertonic: Lots of solute outside —> water LEAVES the cell ○ Hypotonic: Little solute outside —> water ENTERS the cell
Passive Transport
moves molecules WITH the gradient
Active Transport
moves molecules AGAINST gradient (requires energy)
Primary Transport
use energy from ATP to move molecules AGAINST the gradient
Secondary Transport
moves one molecule WITH gradient, and the energy from that moves another molecule AGAINST the gradient (can be symport or antiport)
Pores
open on both sides, very large, not common in euks, mostly beta sheets ie aquaporin in bacteria
Channels
open on both sides, opening can be regulation, can be selective for size (ie ions)
Pumps
“airlock” only one side opens at a time, requires conformational change, uses energy from ATP
Transporters
“airlock” only one side opens at a time, requires conformational change, uses energy from ATP OR driven by gradient
physiological circulating range of glucose
3.6-6.6 mM
GLUT 1
Km (3-7) is around circulating range, thus GLUT one is able to take up glucose and transport it to tissues at a normal range
GLUT 2
Km (17) is much higher than circulating range, can function at high concentrations of glucose without getting saturated and quickly bind and transport it from gut cells to blood. Expressed in the islet cells and other tissues
GLUT 3
Km (1.4) is lower than normal range, thus when glucose levels are low, brain has priority in binding and receiving glucose
GLUT 4
Close to end-range of normal range (6.6), when glucose is higher than normal, insulin can be released and glucose will be stored
Describe the relationship between changes in ligand transport and osmotic pressure, using SGLT as an example.
If more ligand is transported outside of the cell, H2O is sure to follow to maintain equilibrium With SGLT (sodium-dependent glucose transporter), if glucose transport into the cell is disrupted and glucose stays in the lumen, then water moves out of the cell into lumen –> physiologically, this leads to thirst and diarrhea
Selectivity channel
backbone of proteins in the ion channel, ion-specific by size, ie Na+ ion too small to make proper interactions to pass through a K+ channel
Voltage sensor
for K+ channel: protein gate with lots of (+) charged histidines (partially embedded in membrane, so very sensitive), if one side of the membrane has a build up of (+) charge from K+ ions, it repels the voltage sensor and the channel opens until the a less positive charge is re-established and the gate closes
P-type ATPase
○ Has a phosphorylated intermediate state ○ Ion transport including H+
F-type/V-type ATPase
○ H+ transport ○ In lysosome and mitochondria
ABC Superfamily
○ Drugs, lipids, ions, peptides ○ Plasma membrane and ER
Describe the structure of a typical ATP-binding cassette (ABC) transporter.
○ 1, 2, or 4 polypeptide subunits ○ Has 2 TM domains (exoplasmic): § Specific for different ligands § 7 subclasses § Not conserved ○ Has 2 nucleotide binding domains (cytosolic) § For binding ATP
Describe the functional cycle of a typical ATP-binding cassette (ABC) transporter.
- Ligand binds OPEN conformation on cytosolic side 2. ATP binds —> CLOSED conformation —> Ligand released on exoplasmic side 3. ATP hydrolyzed 4. ADP and Pi released —> back to OPEN conformation
