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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?

Na+: outside
K+: inside
Cl-: outside

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?

-Longer axons!
-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


Why is PIP2 important? COmmon?

Rare, <1%. Important for signaling with phospholipase C. Activates calcium release

POINT: phospholipids can have structural and signaling roles.