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Membrane transport


Concentration of substrate required for enzyme to achieve 1/2 Vmax. This is a measure of potency (amt of drug needed for a given effect). lower Km = higher affinity of enzyme for substrate


the maximum rate at which an enzyme can carry out its specified reaction. It occurs when substrate concentrations are so high the enzyme is "saturated"

channels (3 types)

1. Voltage Gated
2. Ligand Gated
3. Mechanically Gated

Voltage Gated Channels

These channels open in response to a change in membrane potential.

Ligand Gated Channels

These channels open when bound by a specific chemical substance (ligand).
EX>muscle contraction, Nervous System

Mechanically Gated Channels

These channels open in response to a physical "pull" on the membrane.
EX>in the ear convert sound waves to electrical signals

P-Type Pumps (3 types)

1. H+ ATPase pump: plants and bacteria
2. Ca++ ATPase pump: on/off switch
3. Na+/K+ ATPase pump: osmotic balance and resting potential in animal cells

Membrane Asymmetry

outer surface of the plasma membrane contains an excess of positively charged sugar groups and the inner surface an excess of negatively charged lipids

Membrane Semipermeability-Macromolecules

Negatively charged proteins (macromolecules) get trapped and help maintain the negative charge inside cell

Membrane Semipermeability-The Concentration Cell

1 M NaCl / 1 M KCl
if only K and Cl ions can diffuse a gradient will be made

Electrogenic Pumps

Pump ions against their gradient

Membrane Potential (4 causes)

1. Membrane Asymmetry
2. Membrane Semipermeability-Macromolecules
3. Membrane Semipermeability-Concentration Cell
4. Electrogenic Pumps

Nernst Equation

V = (RT/ZF) ln Ion (Concentration Outside/Ion Concentration Inside)
Used for 1 ion

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