BIO 3P03 ACTUAL EXAM

BIO 3P03 ACTUAL EXAM

QUESTIONS AND DETAILED ANSWERS |

A+ GRADED ALREADY PASSED

When will diffusion be the fastest between compartments?Correct Answer when there is a large difference in # of molecules between them (flux is proportional to change in conc)

• important properties of ion channels Correct Answer 1) conduct

ions across membrane 2) select specific ions 3) open/close in response to mechanical, electrical, or chemical signals

Even though Na+ is smaller than K+, why doesn't Na+ fit through highly-selective K+ channel (KcsA)? Correct Answer Na+ has stronger electric field, so bigger hydration cloud, thus it behaves bigger than K+ and cannot pass through the K+ channel pores

Which of the following types of ion channels is a monomeric protein? Ligand-gated, gap-junction, voltage-gated. Correct Answer Voltage-gated (all motifs are connected)

In a voltage-gated channel, how many motifs/transmembrane domains? Correct Answer 4

Where is the voltage sensor in a voltage-gated channel? Correct Answer alpha helix 4 (S4) - contains positive amino acids

Where is the selectivity filter in a voltage-gated channel? Correct Answer the P loops between alpha helices 5 & 6 in each domain

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Inside-out patch clamp Correct Answer electrode is quickly withdrawn from cell in cell-attached configuration (exposes inside of membrane to external solution)

• good for studying cytoplasmic factors affecting inside surface of

channel

Outside-out patch clamp Correct Answer electrode is slowly withdrawn from whole-cell mode (exposes outside surface of membrane to external solution)

• good for studying ligand-gated channels (apply ligand to bathing

solution)

Hyperkalemic periodic paralysis Correct Answer mutation alters function of voltage-gated Na+ channels so that they're unable to close inactivation gates.

Triggered by high serum K+ levels & results in periodic muscle paralysis

What does the ion equilibrium potential (Eion) respresent?Correct Answer when electrical gradient = chemical gradient (ie.no net movement)

Formula for Eion Correct Answer Eion = 58mv/z(log [outside]/[inside])

What is membrane potential (Vm)? Correct Answer the difference in voltage across the membrane

How to calculate Vm Correct Answer GHK Equation:

Vm = P[K]o + P[Na]o + P[Cl]i/(P[K]i + P[Na]i + P[Cl]o

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What is the permeabilities for K, Na & Cl-? Correct Answer Pk = 1 Pna = 0.04 Pcl = 0.45

Depolarization is a increase or reduction of charge separation?Correct Answer reduction or reversal or charge separation = depolarization

What ion is most permeable at rest? Correct Answer K+

How do impermeable ions affect the cell? Correct Answer impermeable anions make Vm more negative so Na will influx to balance charge. Since water follows Na, this causes swelling and possible rupture of cell. (water moves towards higher osmolarity)

• conditions of Gibbs-Donnan Eqm Correct Answer 1) [cations] =

[anions] on either side of membrane 2) product of permeable ions inside = outside 3) there is 1 membrane potential, Em = Ek, = Ecl

Applies when ion diffusion is passive.

What is the role of the Na/K ATPase? Correct Answer maintain resting Vm, maintain osmotic eqm, and prevent dissipation of ionic gradients.

• Na out, 2 K in

Actively prevents water from flooding cell by pumping out Na to counter effect of impermeable anions

Steady state vs true eqm Correct Answer steady state requires continuous energy/work eqm does not

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