Lecture 1: Cell Membrane Potential

Question 1

Why can’t ions move across the cell membrane without help?

Answer 1

They are repelled by the hydrophobic phospholipid tails

Ions must cross through channels/ carriers (integral membrane proteins)

Question 2

What’s the difference between carriers and channels

Answer 2

Channels:

• transport protein with a hole in the middle
• usually selective for a particular ion
• ions move down their electrochemical gradient
• amount of movement of ions Is determined by electrochemical gradient
• can be open all the time (leak channels) or gated (only open in response to stimuli)

Carriers:

• transmembrane proteins that change shape
• usually selective for a particular ion
• ions move down their electrochemical gradient
• amount of ion movement is limited by available binding sites ie can be saturated

Question 3

Describe the ionic composition of the ICF and ECF of Na+, Cl- and Ca2+ and K+

Answer 3

Na+, Cl- and Ca2+ high in ECF

K+ high in ICF

Question 4

Give the definition of membrane potential

Answer 4

The difference in charge between inside and outside of a cell at any point in time

Question 5

Give definition of electrochemical gradient

Answer 5

Overall force of an ion due to combination of chemical and electrical driving forces

Question 6

Give definition of equilibrium potential

Answer 6

Value of Vm at which electrical gradient is EQUAL in magnitude and OPPOSITE in direction to the chemical gradient –> no net movement of the ion

Question 7

Do self test at the end of the PowerPoint

Answer 7

Now nigga!