Physio Lect 2 - Solute Transport through the Plasma Membrane

This is the lipid bilayer, what is its use?

Controls the transport of molecules in and out of the cell.

Are the head groups or the fatty acid tails hydrophilic?

the head groups

Are the fatty acid tails in the lipid bilayer hydrophobic or hydrophilic?

hydrophobic

Rank these in terms of ease of transport through the lipid bilayer (easiest to hardest):

hydrophobic molecules (gases)

small uncharged polar molecules (water, urea, and glycerol)

ions

large, uncharged, polar molecules (glucose and sucrose)

1. hydrophobic molecules (gases)

2. small uncharged polar molecules (water, urea, and glycerol)

3. large, uncharged, polar molecules (glucose and sucrose)

   1. ions

how do gases move through the lipid bilayer?

simple diffusion

how do small uncharged polar molecules move through the lipid bilayer?

can go through without aid of proteins, but often movement through bilayer is enhanced through transmembrane proteins creating channels through membrane - concentration difference (for water it would be Aquaporins)

how do hydrophilic solutes (Na+, K+, and glucose) pass through the membrane?

proteins pass through the cell membrane and create channels through the membrane - which then drives the molecules through simple diffusion

what is passive diffusion of ions?

when ions move from high conc to low conc (uses transmembrane protein called an ion channel)

can ion channels be considered as pores for the cell to allow molecules in and out?

yes

how many subunits compose an ion channel in general?

4-5 subunits

how do we tell these channels apart into their subtypes?

they can be repetitions of a single unit or be made up of many different protein subunits, thus making the channels different and distinguishable

Are ion channels selective?

yes

What determines selectivity?

pore size (Na+ is smaller than K+ - but hydration sphere is larger)

amino acid composition

What are the different types of ion channel gates?

Ligand gated

Voltage gated

Mechanically gated

Can there be non-gated ion channels?

yes - some channels are perpetually open

What is facilitated transport?

when a carrier protein transports a defined number of solutes from the extracellular to the intracellular space

how many conformational states do carrier proteins cycle through during facilitated transport?

two or more

what is facilitated transport proportional to?

the solute concentration at low concentrations

what is primary active transport?

when ATP hydrolysis is what drives transport

What is an example of active transport?

Na+-K+ ATPase-I

What happens during Na+-K+ ATPase-I active transport?

we consume 1 ATP per cycle

3 Na+ exit the cell

2 K+ enter the cell

In primary active transport, what is special about this pump?

it’s electrogenic

In Na+-K+ ATPase-I active transport, the transporter consumes about ______ of the cell’s energy

1/3

In Na+-K+ ATPase-I active transport, the transporter consumes about ______ of the NERVE cell’s energy

2/3

What do strong electrochemical gradients influence in cell physiology?

pH balance

osmotic balance

other transport mechanisms

What is the term for when active transport maintains the concentration and electrochemical gradient that serves as the driving force for passive transport, thus letting a second molecule/ion through?

Secondary Active Transport

uniport

symport

antiport

Provide an example of secondary active transport

Glucose Transporters driven by the Na+ Gradient

Glucose binds to a carrier protein that receives Na+ and glucose, using the electrochemical gradient for sodium the cell takes in the sodium ions and the glucose - using the energy to take in sodium as a way to take in glucose

What is the driving force of a channel?

electrochemical gradient

What is the driving force of facilitated transport?

concentration

electrochemical gradient

What is active transport?

energy driven transport against conc. gradient or electrochemical gradient

Transport of a molecule against its concentration gradient utilizing the high electrochemical gradient of Na+ developed by Na+/K+ ATPase is called…

secondary active transport