Week 3 Ch. 4 Flashcards
Cell membranes model
mosaic model
flexible membraes
Factors of molecule transport across cell membranes
- Membrane permeability
- molecular gradients
- Transport mechanisms (membrane pound proteins)
- Ion channels
Membrane permeability
How far into membrane substances can go
High membrane permeability:
O2 and CO2
N2
No membrane permability
Ions, glucose
Diffusion occurs
down a concentration gradient
high–>low
*no ATP needed
Diffusion through a lipid bilayer
Requires a protein channel or carrier
*no ATP needed
Active transport
occurs against concentration gradient
involves a protein carrier
*Requires ATP/energy
Lipid solubility and rate of diffusion
increased lipid solubility = increased rate of diffusion
What soluble molecules cross membrane via
channels or protein transport
What factors influence diffusion?
-Membrane pores (diameter and size)
-Electrical charge (selectivity) - i.e. potassium channel
Potassium Channels MOA
Carbonyl oxygens in selective filter
Carbonyl grabs water that K is surrounded by and pulls K and water apart. K is sucked into channel
Na will not lose water so it just leaves
Sodium channel MOA
Inner surface of channel is lined with negatively charged AAs - pulls dehydrated sodium into channel (pulls sodium away from water)
“all or non”, open or closed
Facilitated diffusion
Transport molecule binds to binding point inside channel
entryway from ECF closes, entryway into cell opens
Molecule releases from binding side and goes into cell
Rate of facilitated diffusion is limited by
Vmax of carrier protein
So facilitated diffusion has a max amount of molecules it can bring in, diffusion rate plateaus off once reached
If you need more molecule, you need addition carrier protiens
Factors that affect net rate of diffusion:
- Concentration gradient
- electrical potential
- Hydrostatic pressure
Electrical potential
Explained by Nerst potential
Nerst Potential
Equilibrium potential
“At what point will the negatively charged molecules stop entering the cell?”
Hydrostatic pressure factor
Higher pressure results in increased energy available
net movement from high to low pressure
Osmosis
water–>salt concentration
Osmotic pressure
amount of pressure required to counter osmosis
attributed to the osmolarity of solution
tonicity vs osmolarity
Tonicity takes into account the properties of the solute AND permeability of a membrane
Tonicity is also called
Effective osmotic pressure
Active transport
requires ATP (energy) to move substances in or out of cell
depends on carrier proteins
Primary active transport
energy is derived from direct breakdown of ATP
Secondary active transport
energy comes from stored energy of ionic concentration differences between two sides of the membrane
Active transport example
Na+-K+ pump
Na-K pump helps:
Maintain negative electrical voltage inside cell (3 Na+ out, 2 K+ in = more negative on the inside)
can run in reverse to generate ATP
Calcium pumps
One pump pumps Ca2+ out of cell, another pumps Ca2+ into organelles (sarcoplasmic reticulum and mitochondria)
Hydrogen ion transport
Pull in H+ against concentration gradient
-gastic glands
-renal tubules (release or pull in H+ to maintain urine pH)
Contratransport
Occurs due to concentration gradients formed on either side of plasma membrane
One substance pulls another in with it when moving into cell
i.e Na+ and glucose
Countertransport
Substance moves into cell and uses energy to propel a second substance out
i.e. Na+ and Ca+
Co-transport
Conformational change of carrier protein will not occur unless both substances are present
i.e. Glucose and Na+ ions
