PHIS 206 Lecture Notes - Lecture 4: Membrane Transport Protein, Facilitated Diffusion, Membrane Potential
2 May 2018
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Lecture 4: Membrane Potential and The Action Potential
Assisted Membrane Transport
• Proteins in the membrane (carriers) aid the passage of solutes and ions across the
membrane
• The motion of the substance can be downhill (facilitated diffusion) or uphill (active
transport)
• Often referred to as “Carrier-Mediated” Transport → something assisting the transport
o Specific (as general rule, will accept 1 thing and not its mirror image) → at
identifying what they want to pass
o Can be competed for
Characteristics of Carrier-Mediated Transport
• Specificity
o Carrier is choosy in what it transports (I’ll take you, but not your mirror image)
• Competition
o Even though choosy, several substances can be transported beyond the intended
one
• Saturation
o The transporters are limited in number. Their collective ability to transport is
therefore limited
Facilitated Diffusion (high to low)
1. Carrier protein takes conformation in which solute binding site is exposed to region of
higher concentration
2. Solute molecule binds to carrier protein
3. Carrier protein changes conformation so that binding site is exposed to region of lower
concentration
4. Transported solute is released and carrier protein returns to conformation in step 1.
Primary Active Transport (low to high)
• Uphill
o Energy is used to move things uphill (from low to high)
o Uses ATP (like spending money)
• (see diagram on slide)
Na-K Pump (pumps sodium out and potassium into cell)
• In every cell, a protein exists that moves sodium out of the cell, and potassium into the
cell against their concentration gradients
• 30% of your caloric intake every day goes to this pump everyday
• As long as this pump is running, the lower chart is true
• The result of this:
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Document Summary
Lecture 4: membrane potential and the action potential. Their collective ability to transport is therefore limited. Primary active transport (low to high: uphill, energy is used to move things uphill (from low to high, uses atp (like spending money) (see diagram on slide) Na-k pump (pumps sodium out and potassium into cell) Ecf (outside of cell) high na+ low k+ Icf (inside of cell) low na+ high k+ Secondary active transport: the fact that sodium is very high outside of cells (and low inside) allows it to be a. As it comes into the cell, it can move something else uphill: this is secondary active transport. This represents as potential , a separation of positive and negative charges: at rest, such cells are said to be electrically polarized (means they are more negative than positive) Graded potential: think ripples on the surface, small depolarization travels away from its origin, slowly dying out.
