Membrane Proteins and Transport across membranes

Question 1

What is an artificial bilayer

Answer 1

There are liposomes (made from cholesterol)
They are impermeable to most soluble molecules

Question 2

Cell membrane

Answer 2

contains membrane transport proteins to transfer specific molecules

Question 3

What are the two types of movement in the bilayer?

Answer 3

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

Question 4

Why are small, non-plar molecules the easiest to diffuse?

Answer 4

The non-polar molecules are hydrophobic and this property makes it easy for these molecules to interact with the hydrophobic tails

Question 5

What type of proteins help transport impermeable molecules?

Answer 5

Transmembrane transport proteins (meaning they cross the lipid bilayer) create a path for ions, sugars, and other polar molecules to cross the bilayer

Question 6

Can transport proteins transport any molecule?

Answer 6

No, these transport proteins are highly selective.
There exist specific transmembrane proteins for certain molecules

Question 7

What are the 2 types of membrane proteins? How do they differ?

Answer 7

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

Question 8

What is the main difference between active and passive transport?

Answer 8

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)

Question 9

What is the electrochemical gradient?

Answer 9

This is the driving force of how many molecules can be transported out

Question 10

What influences the electrochemical gradient?

Answer 10

The concentration gradient + the membrane potential

Question 11

Channel proteins

Answer 11

Assist in passive transport
- they contain hydrophilic pores across the membrane
- They also have a faster diffusal rate compared active transport

Question 12

Ion channels

Answer 12

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

Question 13

What are the types of gated ion channels?

Answer 13

Voltage-gated, ligand-gated (intra/extracellular), mechanical-gated

Question 14

Uniport

Answer 14

Type of transported protein that passively transports one type of solute
-It is reversible (can move in/out of cell)

Question 15

Example of uniport

Answer 15

GLUTuniport- transports glucose

Question 16

What are the three types of active transporters

Answer 16

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

Question 17

what are the two types of gradient-driven pumps?

Answer 17

Symport (solutes move in the same direction)
Antiport (opposite direction

Question 18

NA+-glucose symporter

Answer 18

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)

Question 19

What happens when oscillation occurs

Answer 19

Reversible only if both sides are occupied or if both sites are empty

Question 20

Na+-H exchanger

Answer 20

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

Question 21

How do we fix the issue if Na+ equalizes on both sides of membrane?

Answer 21

Na+-K pumps

Question 22

what are the different types of ATP-driven pumps?

Answer 22

P-type pumps. ABC transporter, V-type proton pump

Question 23

P-type pump

Answer 23

These phosphorylate themselves and this energy will pump nutrients against its gradient

(Na+-K, H+ pumps)

Question 24

Describe the pumping cycle of Na+-K+ pump

Answer 24

1. 3 Na+ or 2 K+ binds to binding site in the cytosol
2. the pump phosphorylates itself, hydrolyzing ATP
3. Phosphorylation triggers conformation changes and Na+ ejected into extracellular
4. 2 K+ binds
5. Pump will dephosphorylates itself
6. Pump returns to original conformation and K+ ejected in cytosol

Question 25

Difference between Na+-K+ pump/H+ pump

Answer 25

Na+-K+ pumps are present in animal cell and H+ are in membrane potential in plant cell

Question 26

ABC transporter

Answer 26

Uses 2 ATP to pump small molecules across membrane
Usually takes toxins away from body

Question 27

V-type proton pump

Answer 27

Uses ATP to pump H+ into organelles to acidify the lumen in lysosomes, plant vacuole

Question 28

how do the V/F type proton pump compare?

Answer 28

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

Question 29

How does our body transfer glucose from our intestines to our bloodstream?

Answer 29

1. 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
2. On the basal lateral side, you can use a GLUT uniporter to move glucose from high to low
3. There is a Na+ pump that will move Na+ out and K+ in

Question 30

List the components involved in moving glucose into intestines

Answer 30

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

Question 31

What is the membrane potential? Why is it important?

Answer 31

Difference in electrical charge on 2 sides of membrane
Used by gradient-driven pumps to carry active transport
Electrical signaling

Question 32

How is a membrane potential generated?

Answer 32

K+ leak channel (cytosol&raquo_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)

Question 33

What is the Equilibrium?

Answer 33

Resting membrane potential varies from -20mV to -200mV

Question 34

Generation if Membrane Potential (AC)

Answer 34

more positive on the outside and more negative on inside