Passive transmembrane diffusion f charged and non charged solutes

Question 1

Definition of Plasma membrane

Answer 1

Cell surface membrane that separates the intracellular fluid from the extracellular fluid
Fluid mosaic model
lipid bilayer- 5 nm thick, 70% of membrane mass (phospholipids and cholesterol)
Membrane proteins: intrinsic -channels, transporters and receptors
extrinsic

trilaminar structure that is shown when stained with osmium trioxide (stains the polar heads)
5 nm thick

Question 2

lipid bilayer

Answer 2

constitutes 50% of the membrane mass and provides the basic membrane structural framework
2 long fatty acid chains attached to the hydrophillic phosphate head group

lipid molecules can diffuse within the plane of their respective leaflets, fluidity is regulated by cholesterol (raises its melting point) and (prevent membrane stifining at low temperatures)

Question 3

Membrane embedded proteins

Answer 3

2nd major component of all cell membranes30% of the mass of membrane, some partially span the lipid bilayer and some fully span the lipid membrane

membrane bound proteins are essential, they can provide structure and biochemical functions.

Question 4

Factors regulating passive diffusion of solutes across the plasma membrane

Answer 4

2 types of potential energy that contribute to the passive diffusion of a molecule or ion across the cell membrane. (chemical and electrical potential energy)

Chemical potential energy difference (from different concentrations of the solute between intracellular and extracellular) this is a potential energy found for both charged and uncharged solutes comes from inherent brwonian forces (concentration gradient -> pushes solute from high to low)

chemical potential difference: RTln [X]i/[X]o

Question 5

Net flux of an uncharged hydrophobic solute

Answer 5

Factors that determine the rate and direction of passive transmembrane diffusion:

net flux (Jx) is defined as the mass of X in moles that passively diffuses across the membrane per unit time per unit area of the membrane (moles/sec * cm2)

can be expressed by ficks first law of diffusion:
Jx= transmembrane concentration difference * Px (permeability)

Px= DB/a D-diffusion coefficient, a- membrane thickness B- partition coefficient (how lipid soluble is it)

Question 6

Electrical potential energy difference

Answer 6

Electrical potential energy difference= ZxF(psii-psio)
z(valency of ion)
(psi electrical potential for X)

transmembrane electrical potential energy (psi o- psi i) results from the difference in electrical charge carried by the extracellular vs intracellular ionic concentrations (positive and negativly charged molecules)

Electrical potential transmembrane energy is set up and maintained by the action of membrane bound active transport systems.

the sum of the chemical and electrical potential energy differences is the electrochemical energy difference (determines the net transmembrane flux of an ion

Question 7

Transmembrane pathways for diffusion of charged hydrophillic solutes (how do the charged hydrophillic solutes beat the odds and get through the lipid barrier)

Answer 7

Ions pass through transmembrane integral protein structures
3 paths:
1. Pores (Cl- pores that exist in skeletal muscle cells and mito outer membrane)
2. Protein Channels: open or closed gate located on the intracellular side of the channel (can be voltage, chemically, or physically gated)
3. transmembrane carrier proteins- forms a conduit and has two gates

Question 8

Equilibrium potentials

Answer 8

when the electrochemical potential energy difference is not 0
when there is no net movement (equilibrium condition) chemical potential energy is equal but opposite to the electric potential energy difference

Vm or Em=(-RT/zF)(ln [X]i/[X]o the nernst equation

Question 9

Differences between intracellular and extracellular concentrations of crucial ions

Answer 9

Na is higher outside (145 to 15) than inside NA want to come inside the cell

K is higher inside the cell (120 to 4.5) than outside K wants to leave the cell

Ca way higher on the outside (1.2), but both concentrations are so small (very low Ca solubility) Ca binds to negative sites on intracellular proteins

Cl is usually higher on the outside but is varient on the EC different