Cell Membranes

Question 1

What are the 5 important cell membrane functions that make electrical events possible?

Answer 1

1. Barriers to free diffusion-differentially permeable allows step up for an ion concentration gradient
2. Produce and release compounds-exocytosis
3. Membrane sensitivity
4. Organize charges across membranes
5. Alter permeability of the membrane such as the concentration gradient to make it permeable to something it wasn’t originally permeable to

Question 2

What is the steady ionic state?

Answer 2

Cells in osmotic equilibrium. Even though cells may be in osmotic equilibrium with their environment The ion concentrations can greatly different between the cytosol and the interstitial fluid. Based on the colligative properties of solutes. osmotic pressure does not care what the particles are just the total conc of solutes

Question 3

How is the difference in the ionic steady state established?

Answer 3

4 Characteristics:

1. Differential permeability of the membrane
2. Concentration gradients of solutes
3. Electrical charge on ion-charge gradient across membrane
4. Active molecular pumps

Question 4

Integration

Answer 4

one system includes the other to have a common outcome.

Question 5

Pradaptations for cell membranes to nervous control systems?

Answer 5

1. integration
2. exadaptation-adaptation to do a specific job used in other ways than originally intended.
3. maladaptation-once useful now not anymore

ex: armadillo

Question 6

How does the steady ionic state maintain the ionic difference across the membrane?

Answer 6

permeability of the membrane

Question 7

What are the five physical and chemical factors that affect permeability?

Answer 7

1. viscosity of the membrane-cholestral/sterols, greater viscosity less permeable
2. thickness of the membrane-greater thickness less permeable
3. presence of protein channels
4. Size of the diffusing molecule-uncharges large mol move slow
5. Charge on molecule- large charged mol move easier bc smaller ions have greater electronegativity

Question 8

What are the two gradients make the driving force?

Answer 8

1. Chemical-potential chemical energy

2. electrical gradient

Question 9

Do we normally measure membrane permeability if not what do we measure and what is it based on?

Answer 9

No. Measure D diffusion coefficient. D is based on the physical parameters in the membrane.

Question 10

What is D and what are the units? And what it is determined by?

Answer 10

General diffusion coefficient and cm squared per second. The physical properties that determine cell membrane permeability: viscosity, thickness, presence of protein channels, molecule size, and charge on molecule.

Question 11

What is conductance in the general diffusion equation?

Answer 11

conductance = AD

A=surface area
D=diffusion coefficient
how easily will a mol be conducted across the membrane

Question 12

What is flow rate?

Answer 12

Driving pressure X conductance

Question 13

What is the chemical potential?

Answer 13

determined by movement of uncharged solutes

closely approximated by concentration gradient. this process is called diffusion.

Question 14

How can we determine the rate of solute movement across the membrane?

Answer 14

Use the general diffusion equation but assume the charge is zero. Also know as Ficks first law of diffusion.

Question 15

Which equation shows how an ion is distributed across the membrane at equilibrium? What two gradients does it account for?

Answer 15

Nernst Equation. Accounts for both electrical and chemical gradients.