Flashcards in Holmes 1 Deck (21):
What is the equation for rate of diffusion?
(concentration of substance) x (membrane surface area) x (substance solubility in membrane)/(membrane thickness) x (square root of molecular weight)
MW not important...everything else clinically relevant
Why is the hydrophobic core of the membrane said to be an insulator? (solution is conductor)
ions and charged molecules do not dissolve in the lipid core of the bilayer
What happens if we got hyperactivity mutation of Ras?
CANCER; cells divide and don't stay where they are suppose to stay
Why is signaling usually at the membrane?
Probability, 5-6 times more likely to make contact between two molecule on membrane than in cytosol
What are three ways molecules are transported across lipid bilayers?
1) passive diffusion: not protein facilitated
2) passive transport: protein dependent
3) active transport: protein and energy dependent. Common is secondary active transport using ion gradient (sodium, potassium, and chloride are common ions)
-also symporters and antiporters
Describe the rate graph of passive diffusion, transport, and carrier-mediate transport.
passive diffusion: linear, slow but does not saturate
passive transport with channels: fast, but does saturate (similar to michaelis-menten)
carrier-mediate transport: faster than passive diffusion but slower than channel mediate transport. Does saturate. Passive carrier transport can't transport above concentration gradient, but active transport can.
What is the function of the plasma membrane?
Physical barrier: allows for build up of gradients
Communication interface: supports signal transduction
Na+ higher inside or outside cell? K+? Cl-?
Why is Ca2+ concentration so low inside the cell?
Ca2+ precipitates easily
Nomenclature for high/low K+? Na+? pH?
K+: hyper/hypo -kalemia
Na+: hyper/hypo -natremia
pH: alkalemia, acidemia
Passive membrane properties include:
-maintaining high charge separation across membrane and high currents
-both requires energy
Where does a membrane with low capacitance help the most?
-small capacitance allows electrical signal to travel faster with smaller attenuation
Ohm's Law? Time constant?
V = IR, R=resistance, I=current, V=voltage
t = RC (membrane resistance x membrane capacitance)
-for FAST propagation, we want small t
length constant = ?
square root of membrane resistance (Rm)/internal resistance (Ri)
FAST propagation we need large length constant (lambda)... LARGE Rm...small Ri
Rm is like "insulator" makes it propagate faster
How can we decrease capacitance to increase Rm?
Increase d, the separation between the two sides of the membrane
ANSWER: MEMBRANE STACKING....since we can't just increase d alone (myelin sheath is an insulator)
C -> s/d Rm -> d/s d is membrane thickness, s is membrane surface
What is multiple sclerosis (MS)?
demyelinating disease, increases membrane capacitance, decreases nerve conduction velocity
-inflammatory autoimmune disease that destroys oligodendrocytes
How do we get ions across the membrane if they act as insulators?
ion channels and transporters
-ion channels often have multiple subunits which each have multiple transmembrane segments
-ion selectivity region is SELECTIVITY FILTER
What is Nernst potential?
when electrochemical driving force = 0, and ion is at equilibrium
V = RT/zF x ln[ion outside]/[ion inside]
rewritten V = 62/z x log10 [ion outside]/[ion inside]
z = valence of ion (K+ = 1, Cl- = -1)
What tissue is notably targeted by hyperkalemia? Risk groups?
The heart. Those with chronic renal failure are at high risk.
Look and study PKG?
I dont know if we need to know
What are 3 major phospholipids?
-phosphatidylethonolamine (net positive charge)
-phosphatidylserine (net negative charge): on inner leaflet