Chapter 10

Question 1

•What are passive diffusion and the types of molecules that can move across the membrane in this fashion?

Answer 1

Simplest form of diffusion
During passive diffusion, a molecule simply dissolves in the phospholipid bilayer, diffuses across it, and then dissolves in the aqueous solution at the other side of the membrane.
Gases ( C02, N2, O2)
Small uncharged polar molecules ( Ethanol, and water, urea kinda)

Question 2

• Be able to calculate the free energy required to move a molecule or ion across the membrane.

Answer 2

∆G_A = RT ln ([A]_in/[A]_out)+Z_Aℱ∆Ψ

∆G_A- Electrochemical potential of A (per mole)
R – Ideal Gas constant (8.314 J/mol K)
T – Temperature in Kelvin
ℱ- Faraday’s constant (96,485 J/Vmol )
Z_A – ionic charge of A
∆Ψ- Membrane potential (volts)

Question 3

• Mediated diffusion
  
  • What are carriers?

Answer 3

■ Carrier binds to ion and diffuses through membrane

■ Ionic complexes are soluble in nonpolar solvents

Carrier ionophore: Valinomycin

six Val carbonyl oxygens coordinate the K+ ion

■ Methyl and isopropyl groups let is pass through membrane

Question 4

• Mediated diffusion
  
  • What are channels?

Answer 4

■ Movement down concentration gradient

■ Selective

■ Can be gated or non-gated

Aquaporin AQP1

■ Specific for water

■ No transport of H+ or H3O+

Size restriction

■ Electrostatic repulsion

■ Water dipole reorientation

A= Ala; H=His; N=Asn; P=Pro; R=Arg

-Gated ion channels, allows ions to enter and go out the membrane in response to the voltage changes. One great example of gated ion channel is the voltage gated. On the other hand, non-gated ion channels open and closes the channel gates without the voltage changes.

Question 5

• Mediated diffusion:
  
  • What are transporters and how do they work?

Answer 5

Slower rate of movement than channels

■ Conformational changes

■ Uniporter – Moves molecules down concentration gradient

GLUT1 uniporter

Selective for glucose

■ Alternates between two conformations

■ Can move glucose in either direction across membrane

Question 6

• Define active transport. Describe the difference between primary and secondary active transport.

Answer 6

• Against a concentration gradient
• An energy source is used during transport § Primary active transport
• Energy source is ATP, photons of light, or electrons moving down an ETC § Secondary active transport
• Energy source is a previously established electrochemical gradient

Question 7

• What is the mechanism and of movement of ions through the Na⁺/K⁺ ATPase.

Answer 7

■ Primary active transport of ions across the membrane

■ Antiport

– 3 Na+ out

– 2 K+ in

■ Controls osmotic potential

■ electrogenic

Question 8

• How does the movement of ions or molecules through symporters and antiporters work?

Answer 8

Secondary active transport

■ Slower rate of movement than channels

■ Conformational changes

■ Cotransporters – Couples the movement of a molecule down its concentration gradient with the movement of a molecule against its concentration gradient