Quiz 4 (aka work from home assignment 1)
Before you attempt the following questions, please review chapter 12 lecture slides 1 through 30. Feel free to read the textbook and other sources as necessary. The videos help too.
The plasma membrane acts as a selectively permeable barrier, keeping cellular contents in, and the other things out.
Transporter proteins facilitate movement of certain molecules across the plasma membrane.
Thanks to selective permeability, many molecules are found at differing concentrations across the plasma membrane when a cell is at rest.
Solute Extracellular Intracellular
Ion channels are another class of protein that can selectively allow ions to cross the plasma membrane.
Neurons are a specialized class of cells that can transmit information from one place to another by selectively changing the concentration gradient of certain ions in response to a stimulus.
Immediately after a neuron is stimulated, a second class of ion channel opens, called a potassium rectifying channel.
When an electrode is stuck inside an intact squid giant axon, the membrane potential registers
-70mV. When the axon, suspended in a bath of seawater, is stimulated to conduct an impulse, the membrane potential changes transiently to +40mV. For univalent ions at 20oC, the Nernst equation reduces to:
V = 58mV x log10(Co/Ci)
Where Co and Ci are the extra and intracellular concentrations of the ion respectively (see table below).
Ion [cytoplasm] [seawater]
Na+ 65mM 430mM
K+ 344mM 9mM
Using this equation, calculate the potential across the resting membrane;
(Make sure to show how you rearranged the equation to solve for the unknowns).
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