Membrane Proteins and Transport across membranes Flashcards
What is an artificial bilayer
There are liposomes (made from cholesterol)
They are impermeable to most soluble molecules
Cell membrane
contains membrane transport proteins to transfer specific molecules
What are the two types of movement in the bilayer?
Simple diffusion which takes place by molecules moving from high to low concentration
- small non-polar molecules have the fastest diffusal rate (highly permeable)
- small polar molecules still undergo simple diffusion, however there is more of a barrier compared to non-polar molecules
Membrane transport proteins foster the second type of movement through the membrane, which transfers large polar molecules/ ions through the bilayer
Why are small, non-plar molecules the easiest to diffuse?
The non-polar molecules are hydrophobic and this property makes it easy for these molecules to interact with the hydrophobic tails
What type of proteins help transport impermeable molecules?
Transmembrane transport proteins (meaning they cross the lipid bilayer) create a path for ions, sugars, and other polar molecules to cross the bilayer
Can transport proteins transport any molecule?
No, these transport proteins are highly selective.
There exist specific transmembrane proteins for certain molecules
What are the 2 types of membrane proteins? How do they differ?
Channels and Transporters
- Channels bind weakly to the transported molecules, whereas transporters bind strongly to the transported protein
- Channels decide which proteins to transport based on size and electrical charge, but for transporters proteins bind to binding site of specific transports
- channels do not change conformation, but transporters change shape and conformation
What is the main difference between active and passive transport?
Passive transport refers to simple diffusion where molecules move along the concentration gradient, from high to low concentration
Active transport involves energy to pump molecules from low to high concentration (moves against concentration gradient)
What is the electrochemical gradient?
This is the driving force of how many molecules can be transported out
What influences the electrochemical gradient?
The concentration gradient + the membrane potential
Channel proteins
Assist in passive transport
- they contain hydrophilic pores across the membrane
- They also have a faster diffusal rate compared active transport
Ion channels
there exist non-gated ion channels that are always open and these channels assist in generating resting potentials
- There are also gated channels, which require specific electrical signals to open
What are the types of gated ion channels?
Voltage-gated, ligand-gated (intra/extracellular), mechanical-gated
Uniport
Type of transported protein that passively transports one type of solute
-It is reversible (can move in/out of cell)
Example of uniport
GLUTuniport- transports glucose
What are the three types of active transporters
Gradient-driven pump: one solute moves down the gradient, producing energy that will force a second solute to move against the gradient
ATP-driven pump
Light driven pump
what are the two types of gradient-driven pumps?
Symport (solutes move in the same direction)
Antiport (opposite direction
NA+-glucose symporter
Sodium moves down the concentration and glucose moves against the gradient in one direction
1. occluded (empty)
2. outward (open Na+-glucose put into binder)
3. occluded (occupied)
4. inward (open in cytosol)
What happens when oscillation occurs
Reversible only if both sides are occupied or if both sites are empty
Na+-H exchanger
Example of an antiporter
There needs to a pH maintained to ensure optimal enzyme function in the cytosol
Sometimes there is an excess in H so the transporter will transport H out of cytosol as Na moves in
How do we fix the issue if Na+ equalizes on both sides of membrane?
Na+-K pumps
what are the different types of ATP-driven pumps?
P-type pumps. ABC transporter, V-type proton pump
P-type pump
These phosphorylate themselves and this energy will pump nutrients against its gradient
(Na+-K, H+ pumps)
Describe the pumping cycle of Na+-K+ pump
- 3 Na+ or 2 K+ binds to binding site in the cytosol
- the pump phosphorylates itself, hydrolyzing ATP
- Phosphorylation triggers conformation changes and Na+ ejected into extracellular
- 2 K+ binds
- Pump will dephosphorylates itself
- Pump returns to original conformation and K+ ejected in cytosol
Difference between Na+-K+ pump/H+ pump
Na+-K+ pumps are present in animal cell and H+ are in membrane potential in plant cell
ABC transporter
Uses 2 ATP to pump small molecules across membrane
Usually takes toxins away from body
V-type proton pump
Uses ATP to pump H+ into organelles to acidify the lumen in lysosomes, plant vacuole
how do the V/F type proton pump compare?
They are structurally related but F-type pumps use H+ gradient to drive synthesis of ATP
in mitochondria, chloroplasts. bacteria
F-type ATP synthase pumps H+ into matrix and is reversible
V-type pumps H+ in lumen
How does our body transfer glucose from our intestines to our bloodstream?
- glucose must go through the cell from a low concentration (inside lumen) to high concentration (inside cell) through a Na+ driven glucose symport.
The energy from Na+ moving from high to low will move glucose against gradient - On the basal lateral side, you can use a GLUT uniporter to move glucose from high to low
- There is a Na+ pump that will move Na+ out and K+ in
List the components involved in moving glucose into intestines
Gut lumen
Epithelial cell: forms villus/villui and in villus we have microvillus
Apical domain: face gut lumen
Lateral domain: faces neighboring cells
basal domain: faces basil lamina
Tight junctions: blocks things from going in/out
What is the membrane potential? Why is it important?
Difference in electrical charge on 2 sides of membrane
Used by gradient-driven pumps to carry active transport
Electrical signaling
How is a membrane potential generated?
K+ leak channel (cytosol»_space; extracellular space)
Na+-K+ pump ( 3 Na+ pumps out of cytosol from a low to high and 2 K+ pumps into cytosol from high to low)
What is the Equilibrium?
Resting membrane potential varies from -20mV to -200mV
Generation if Membrane Potential (AC)
more positive on the outside and more negative on inside
