Membrane Transport

Question 1

Which molecules are easily able to get across the lipid bilayer? Which have the hardest time?

Answer 1

High: Water
Middle: Urea, glycerol, glucose
Low: Cl-, K+, Na+

Question 2

Which cells are high intracellularly? Extracellularly?

Answer 2

Intracellular: K+, Mg+2, SO4-2,PO3-, protein
Extracellular: Na+, Ca+2, Cl-

Question 3

What is the difference between diffusion and active transport?

Answer 3

Diffusion- down concentration gradient with carrier, channel or just across the membrane
Active- against concentration gradient with ENERGY

Question 4

How is simple diffusion different from facilitated diffusion?

Answer 4

Simple: dependent only on concentration gradient
Facilitated: rate of diffusion limited by Vmax and density of carrier protein

Question 5

What types of carrier proteins/channels are there involved in diffusion?

Answer 5

1. Lipid-soluble cross membrane- determined by lipid permeability
2. Water-soluble
   A. Pores-determined by diameter and electrical
   charge
   B. Channels- selectively permeable, voltage
   gated, ligand gated

Question 6

What is an ionophore?

Answer 6

Hydrophobic molecules that dissolve in lipid bilayer that mediate passive transport by increasing permeability to specific inorganic ions.

1. Mobile ion carriers (Valinomycin) pick it up and carry it across
2. Channel formers (gramicidin A) form pores-faster than carriers

Question 7

What factors affect net rate of diffusion?

Answer 7

1. Concentration difference
2. EMF (=+or-61(logC0/Ci))…nernst potential
3. Pressure difference

Question 8

What is osmotic pressure? Osmolarity? How does osmolarity change for ionic compounds?

Answer 8

Osmotic pressure- the amount of pressure required to counter osmosis.
Osmolarity- determines osmotic pressure-number of particles in a soln. Mw=1 osmole
It changes based on the number of particles it would disassociate to; for NaCl, it would double.

Question 9

What is the difference between isotonic and isosmotic?

Answer 9

Isotonic is the same pressure and isosmotic is same osmolarity. Isotonicity and isosmoticity are both positive for molecules that don’t cross the membrane unaided, but ones that can are only isoosmotic.

Question 10

How is steady state determined? How does permeability affect the time course?

Answer 10

Concentration of impermeant molecules because permeant molecules are constantly going in and out…molecules with higher permeability like urea change the volume more rapidly

Question 11

What are some clinical abnormalities of fluid volume regulation?

Answer 11

Hypernatremia- increased plasma Na…increases water loss, central/nephrogenic diabetes insipidus
*decreased ADH secretion/responsiveness to ADH
Hyponatremia- decreased plasma Na…large water ingestion, SIADH

Question 12

What is the difference between primary and secondary active transport?

Answer 12

Primary- directly uses ATP

Secondary- uses energy from another molecule’s concentration gradient
example:

Question 13

What are examples of primary transport?

Answer 13

Na+/K+ ATPase pump for maintaining osmotic balance
Ca+2 ATPase on cell membrane and SR to keep Ca out of cytosol
H+ ATPase HCl secretion in GI and kidney to control pH

Question 14

What are two subtypes of secondary active transport?

Answer 14

1. Co-transport: substance transported in same direction as other molecule’s [gradient]
2. Counter-transport: driven in opposite direction

Question 15

How do cardiac glycosides (digotoxin) increase cardiac contractility?

Answer 15

Inhibit the Na/K ATPase= increase intracellular Na–>decrease Na gradient–>decrease Na/Ca counter-transport–> increased intracellular Ca for mm contraction