Active Transport Through Membranes Flashcards
What are the 4 major groups of molecules that come into contact with the cell membrane?
Rank which can pass through the lipid bilayer from best to worst efficiency
Hydrophobic Molecules- Best (O2, CO2, N2, steroids, hormones)
Small, Uncharged Polar Molecules (H2O, Urea, Glycerol, NH3)
Large, Uncharged Polar Molecules (Glucose, Sucrose)
Ions- Worst (H+, Na+, HCO3-, K+, Ca2+, Cl-, Mg2+)
Describe Passive Transport
No E needed
Solute travels down concentration gradient
Describe Active Transport
Coupled to ATP hydrolysis
Solute travels against the concentration gradient
What are the 3 modes of transport?
Antiporter- two molecules in the opposite direction
Symporter- two molecules in the same direction
Uniport- one molecule in one direction
What are the 3 general categories of Transporters?
- Pumps perform primary active transport- A water pump FIGHTS GRAVITY and actively pulls water in
- Carriers traverse the membrane without needing (extra) energy- Carrying a STOWAWAY along for the ride
- Channels are used in passive transport
What are the 4 types of primary active transport pumps?
P-type pump –> Phosphorylates self
ABC Transporter –> ATP Binding Cassette
V-type pump –> Uses ATP (1st found in yeast Vacuoles)
F-type pump –> Makes ATP (Phosphorylation Factor)- Factor V in ETC
Where are the 3 locations of P-type ATPases and what ions move in/out at each location?
Universal:
Ions moving in (2 K+ to cytosol)
Ions moving out (3 Na+ to outside)
Muscle:
Ions moving in- N/A
Ions moving out (2 Ca2+ to SR)
Stomach:
Ions moving in (1 K+ to cytosol)
Ions moving out (1 H+ to stomach)
For the 3 locations of the P-type ATPases, what is the function/role each participates in?
Universal:
Electrical excitation (neurons/muscles)
Gradient driving active transport
Muscle- Ca2+ signaling
Stomach- Digestion/Gastric pH
What are the 4 domains of P-type ATPases?
What are 2 Examples?
- Transmembrane domain spans the lipid bilayer. It is an integral membrane protein
- A/Actuator domain links the cytosolic domains to the transmembrane domain
- N/Nucleotide binding domain binds ATP
- P/Phosphorylation domain accepts the phosphate from ATP
Example 1: SERCA
Example 2: Na/K Pump
What is the MOA for the Primary Active Transport of P-Type ATPase SERCA?
- E1, unphosphorylated, Ca2+ ions bound
- ATP binds, Ca2+ ions trapped
- ATP hydrolysis, self-phosphorylation
- Eversion to E2, Ca2+ ions released
- Release of inorganic phosphate
- Eversion to E1
- E1 Sate: Open Inside
- E2 State: Open Outside
What is the MOA for the Primary Active Transport of P-Type ATPase Na/K pump?
- E1 Na+ ions bound, ATP bound
- Na+ ions trapped
- ATP hydrolysis, self-phosphorylation
- Eversion to E2, Na+ ions released
- Binding of K+
- K+ ions trapped, release of inorganic phosphate, ATP rebinding
- Eversion to E1
- Release of K+
- E1 Sate: Open Inside
- E2 State: Open Outside
For primary active transport, Digitalis and Oubain both lock the _____ _____ in the ____ _______.
What does this do to the cell?
Na/K pump
E2 conformation
This keeps Na+ inside the cell –> Excess Na+ removed by exchanging with Ca2+ –> Makes Ca2+ makes heart contract
Describe the MOA for primary active transporters- ABC Transporters
What are 2 Examples?
- Empty Transporter
- Small molecule binds and is trapped; ATP binding site affinity increases
- 2 ATPs bind causing eversion
- Small molecule is released
- ATP hydrolysis and release
Examples:
MDR protein- Monomer
MsbA- Homodimer
What are 2 examples of secondary active transport?
Na-Glucose cotransport
Lactose Permease
*Note that by definition, all secondary active transporters are symporters
Describe the MOA of secondary active transport Lactose Permease
- Empty carrier, H+ binds and increases affinity for lactose
- Lactose binds
- Eversion
- Lactose released
- Deprotonation
- Eversion
