04_Membrane Transport Flashcards
What molecules can diffuse freely through the membrane?
Hydrophobic molecules (O2, CO2, N2, steroid hormones)
Compare the diffusion of uncharged polar molecules and ions through the lipid bilayer.
Small uncharged polar molecules > large uncharged polar molecules > ions
**ions CANNOT diffuse freely through membrane.
What does the ∆G during diffusion depend on for nonelectrolytes and electrolytes?
non-electrolytes: concentration (chemical) gradient
electrolytes concentration & voltage (electrochemical) gradient
How are protein pores used for transport?
Used as ion channels (typically votage-gated)
PASSIVE transport
What form of transport is the glucose transporter used for? How is the subsequent exit of glucose prevented?
Facilitated diffusion
Once inside the cell, glucose is phosphorylated.
What are some key features that set facilitated diffusion apart from diffusion (apart from the involvement of a transporter)?
Facilitated diffusion is specific, it is saturable (reaches a max rate of solute movement), and is regulated.
Simple diffusion is not (on a all counts).
How do primary pumps function? What do they typically transport?
hydrolyze ATP to move IONS against their concentration gradient.
Which type of primary pump is found in all cell types? What does it typically transport?
P-type pymp transports ions (Na+, K+, Ca2+, H+)
Which types of primary pumps can create proton gradients?
V-type and F-type
and also P-type
Which type of primary pump is composed of a dimer? What does it usually transport (general category)?
ABC transporter
transports small lipophilic molecules
How do P-type pumps achieve necessary conformational ∆ for functioning?
phosphorylation
Why is Ca+ a good signalling ion?
The ionic gradient is MUCH greater outside the cell compared to the cytosol; therefore, a small ∆ can be detected.
In which organelles is Ca+ very abundant?
mitochondria and ER
What type of pumps are found in membranes vesicles, vacuoles and lysosomes?
V-type pumps
Apart from the ions they transport, what is a main difference between P- and V-type pumps?
P-type pumps are phosphorylated. In V-type pumps, the phosphate from ATP hydrolysis is not transferred to the pump.
Which type of pumps can be made to “run backwards”? What does this mean?
F-type pumps
running backwards results in production of ATP from an existing ion gradient
What are flippases? Which type of primary pumps can act as flippases?
Flippases move lipids in the bilayer from one leaflet to the other (flip-flop movement).
ABC transporters can function as flippases.
How do Na+/K+ pumps function? What type of pump are they?
P-type primary pumps
They move Na+ and K+ against their concentation gradients.
E1 conformation: 3 Na+ bind in cytosolic side; ATP hydrolysis & phosphorylation of pump –> conformation change to E2.
3Na+ released into extracellular space. 2K+ bind
–> conformation change to E1, 2K+ released into cytosol.
SUMMARY: 3Na+ out, 2K+in
What is ATP used for in secondary active transport?
ATP is used to create concentration gradient for one molecule, that will be then used to drive transport for OTHER molecules.
Describe the movement of the molecule being transported with relation to the driving ion in symport and antiport.
Symport: driving ion moves down its concentration gradient in the SAME direction that the specific molecule is moving AGAINST its concentration gradient.
Antiport: specific molecule moves against its concentration gradient in the OPPOSITE direction of the driving ion moving DOWN its concentration gradient.
