Lecture 5: Membrane transport

Question 1

GPI anchors are only on the

Answer 1

extracellular leaflet

Question 2

Passive transport +ex (3)

Answer 2

• Does not require energy input from the cell
• Occurs by diffusion (movement from a region of high concentration to low concentration)
• Through membrane, channel or facilitative transporter

Question 3

Active Transport+ ex (3)

Answer 3

• Does require energy input (ATP) or the flow of other substances down their concentration gradient (secondary active transport)
• Can move substances against a concentration gradient
• Examples: Pumps

Question 3

Ion channels vs Facilitative transporter (2)

Answer 3

1. Ion channel allow millions of ions pass through per second, FT allows 100-1000 molecules per second
2. Facilitative transporters bind to specific molecules and undergo large conformational changes to facilitate their movement, while channels form pores allowing passive movement of ions or molecules along their concentration gradient and small change.

Question 3

The kinetic graph for facilitative transporter

Answer 3

When the concentration is high, the rate of transport levels off

Question 3

Primary active transport (3)

Answer 3

1. P-type pumps
2. V-type pumps
3. ABC transporter

Question 3

Facilitative Transporter (2)

Answer 3

• Binding of the solute triggers a confirmatinal change in the transmembrane protein that expose the solute to the other side
• polar or charged molecules (ex: glucose or amino acids)

Question 3

GLUT4 (5)

What is it+ex of what type of transporter?+ binding creates+ continued diffusion + direction

Answer 3

• Glucose transporter
• ex of a facilitative transporter
• Binding of glucose to one site provokes a conformational change associated with transport, and releases glucose to the other side of the membrane.
• Continued diffusion of glucose in the cell is possible because as it reaches the inside of the cell it is rapidly phosphorylated so the concentration of glucose in the cell is always low
• Bidirectional as it moves glucose high to low

Question 4

Channels (2)

Answer 4

• ions and water
• Small change (open/closed) in response to voltage,
  ligand, or mechanical change. [In the case of ligand-
  gated, the solute transported is not usually the ligand.]

Question 5

P-type pump

Answer 5

• Becomes phosphorylated during active transport
• Ex: Na+/K+-ATPase

Question 6

Na+/K+-ATPase

Answer 6

• During active transport, becomes phosphorylated and ATP is hydrolyzed
• Contributes to mainintaining the membrane potential (voltage) in cells
• 3 Na+ pumped out, 2K+ pumped in

Question 7

Na+/K+-ATPase Steps (8)

Answer 7

1. E1 conformation: ion binding sites are accessible on the inside of the cell, High affinity for sodium ions, ATP is bound
2. Occluded E1 state: When ions are bound, the protein closes so bound sodium ions cant flow back
3. Hydrolysis of ATP, pump is phosphorlayed, ADP still bound
4. E2: Release of ADP and conformation changes to E2, Ions binding sites are accessible to the extracellular compartment, loses affinity got Na+ ions, high affinity for potassium ions
   - 5/6. Occluded E2: When ions are bound, the protein closes, dephosphorylation occurs where phosphate falls off the pump
   - 7/8. E1 conformation: ATP binds, protein returns to E1 conformation, low affinity for K+ ions

Question 8

Rate of transport for ion channels and P-type pumps

Answer 8

• Due to complex conformational changes, the rate of transport is much slower for p-type pumps than transport through ion channels (by several magnitude)

Question 9

Proton-potassium pump (3)

What type+the dynamics when food is present +what it does

Answer 9

• H+/K+-ATPase is a p-type pump
• When food is in the stomach, pump is active as it fuses to plasma membrane as vesicles takes them there
• carries out the transport of protons for potassium ions through the energy in ATP hydrolysis (ATP-> ADP)

Question 10

V-Type pumps (2)

fuel+ what it does

Answer 10

• Utilize ATP energy without becoming phisphorylated themselves
• a proton pump that uses the energy from ATP hydrolysis to produce a proton gradient by transporting H+ ions across organelles and vacuoles (maintain the low PH of lysosomes)

Question 11

ABC transporters

Answer 11

• ATP-binding cassette transporters
• Share a similiar structure of ATP binding domain
• ABC transporters utilize the energy of ATP binding and hydrolysis to transport various substrates such as ions, lipids, peptides, nucleosides etc. across cellular membranes.

Question 12

Concentration gradient (2)

What it is+ a form of energy….

Answer 12

• The difference in the concentration of a substance between two areas
• a form of stored potential energy

Question 13

Symporter

Answer 13

• Transports two substances in the same direction
• Also called co-transporter

Question 14

Antiporter

Answer 14

• Transport two substances in the opposite directions
• Also called exchanger

Question 15

Secondary active transport

Answer 15

One of the substances is moving along (with) its concentration gradient, providing the energy to move the other substance against its concentration gradient

Question 16

Na+/Glucose cotransporter

Answer 16

• Transport glucose from the intestinal lumen into epithlial cells and Na+ ions is low in concentration inside the cells. So the Na+ ions moving down their concentration gradient is used to drive the cotransport of glucose
• Sodium provides energy for glucose to move against its concentration gradient
• Both move in the same direction