Membrane Transport Flashcards
What can go directly through a cell membrane?
Small non polar molecules (e.g. O2, CO2), Steroid hormones
What is Osmosis?
Net movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration
What does osmolarity and osmolality mean? What is the difference?
They both refer to the total concentration of solutes in a solution.
Osmolarity has the units Osm/L while Osmolality has the units Osm/kg.
Osmolarity varies with temperature and pressure while Osmolality is independent of temperature and pressure.
In Osmolality, volume includes solvent and solutes while in osmolality total weight is only of solvent
What is an osmole?
The number of moles of solutes that contribute to the osmotic pressure of a solution.
We only take into account the solutes that cannot cross the cell membrane
What does Tonicity mean?
It is the solute concentration of a solution outside a cell and its effect on cellular fluid volume. Therefore, you always need a cell and its surrounding solution to measure tonicity so that you can make a comparison.
You can have hypertonic, isotonic and hypotonic solutions
What affects membrane potential?
The concentration of ions (e.g. Na+ and K+).
What is Simple Diffusion?
Movement down a concentration gradient for molecules that can cross the lipid membrane by themselves (no proteins involved)
Does not require energy.
What does hypertonic and hypotonic mean?
Hypertonic means there is a higher solute concentration outside of the cell (lower osmolarity inside cell) so water moves out of the cell. This causes cells to shrink.
Hypotonic means there is a higher solute concentration (higher osmolarity inside cell) inside the cell so water moves into the cell. This causes the cell to swell.
What is facilitated diffusion?
Molecules use proteins to transport molecules to the other side of the membrane down a concentration gradient.
Does not require energy
What are transmembrane protein examples? Are they hydrophobic or hydrophilic
Channel and Carrier proteins. They have hydrophobic outer membranes so they sit well with the inner membrane which is hydrophobic. Then they have hydrophilic inner membranes which allow hydrophilic molecules to easily pass through them.
Are channel proteins always open?
They can be.
Or they can be closed in a process called gating. The overall shape of the protein stays the same but a small portion of the membrane acts a gate. For example, in changes in pH, Osmotic pressure, membrane potential or binding of molecules (e.g. sodium ion voltage gated channels)
There is no limit to the number of molecules that can pass through a channel protein at any one time.
How do carrier proteins work?
Molecules bind to a carrier protein leading to a change in the shape of the carrier protein. There is a limit to the number of molecules that can move through the carrier protein at any one time.
What is active transport?
It transports solutes against the concentration gradient.
Active transport requires energy, usually under the form of ATP.
What is secondary active transport?
They use the gradient created by another active transport pump (e.g. sodium potassium pump) to move molecules down their concentration gradient by co-transport via a symporter.
What is an antiport?
When different molecules are pumped through an active transport protein in different directions (e.g. sodium calcium pump- 3 Na+ in for 1 Ca+ out)
