membrane transport Flashcards
ions found mostly in extraceullar fluid
Na and Cl
ions found mostly in cells
K and PO43+
rate of solute movement across a membrane
P x C
where P is the permeability coefficient and C is the concentration gradient
hydrophobic molecules
diffuse easily across the membrane
O2, CO2, N2, steroid hormones
small uncharged polar molecules
kinda go through the plasma membrane
water, urea, glycerol, NH3
large uncharged polar molecules
mostly don’t go through the membrane
glucose and sucrose
ions
don’t go through the plasma membrane at all
protons, sodium, HCO3-, K+, Ca2+, Cl-, Mg2+
osmolarity
the concentration of everything but water
why is osmolarity sometimes hard too calculate
- Depends on how much stuff dissociates
- Osmolaritty of proteins and macromolecules hard to predict depends on dissociation
osmolarity of intracellular fluid
- Osmolarty of intracellular fluid is 300mOsmol/L
aquaporins
channel allowing water to move
allows bidirectional movement
tonicity
whether a cell swells or shrinks due to osmosis
isotonic
cell stays the same size
hypertonic
has more solutes so the cell shrinks
hypotonic
has less solute so the cell swells or bursts
iso osmolar
same osmotic value
why is iso-osmolar not the same as isotonic
solutes can move through membrane as well
when is iso osmolar the same as isotonic
when dealing with solutes that don’t move across the membrane
channel and transporter mediated transport is powered by
concentration gradient
pump mediated transport is powered by
ATP
pores and channels
- Water filled pores and channels increase permeability
- Pores and channels can be selective eg. Aquaporin for water
- Channels are gated pores allow control of permeability
channels are different to pores because
- Channels are gated pores allow control of permeability
3 types of gated channels
mechanically gated, ligand gated, voltage gated
mechanically gated channels
shut when there is no tension
ligand gated channels
○ Chemical molecule - ligand - opens the channels
○ Can be extracellular or intracellular ligand
voltage gated channels
○ Most cells are negative on the inside and positive on the outside
○ When the voltage changes the channels open
carrier proteins and transport proteins
- Facilitated diffusion
- Conformational change -> transport
- Energy from concentration gradient
uriporters
○ Transport a signle solute from one side of the membrane to another
- Co-transporters
○ Transfer of one solute depends on the simultaneous transport of a second solute (coupled transport)
2 types of co transporters
○ Symporters
§ Transfer second solute in the same direction as the first
○ Antiporters
§ Transfer the second molecule in the opposite direction tto the first
SGLT1
- Sodium-dependant glucose transporter
- Na+ and glucose transport
- Symporter
Active transport - pumps
- Pumps use the chemical potential energy to pump molecules up hill against their concentration gradient
- The pump is effectively a carrier being forced to operate in reverse (both are called transporters/facilitated diffusion)
ATP-binding cassette transporters - ABCs
- bind specific molecules and use ATP energy to transport them across phospholipid bilayers
- Huge superfamily (many transporters = many target molecules)
ABC transporter example
ABCA/ABCG - exports cholesterol out of cells
The Na+/K+ pump
- Uses ATP
- Antiporter
- All cells have this pump and it uses 33% of it’s cellular energy
how many ions does the NA/K pump transport
- Pumps 3x Na+ put and 2x K+ in per cycle
- Uses 1xATP molecule
electrical effect of Na/K pump
- Electrogenic - net movement of +ve charge out of cell
inside of the cell is charged
negatively
secondary active transport
establishing the Na/K gradient and using it to pump other things in and out of the cell
example of secondary active transport
SGLT1 symporter of Na and glucose
allows glucose uptake
2 types of exocytosis
constitutive and regulated
constitutive exocytosis
§ Produce a protein and put it in a vessicle and it has unregulated membrane fusion
regulated exocytosis
§ Regulated membrane fusion
endocytosis
○ Big things (phagocytosis), little things (pinocytosis)
○ Can be highly specific (receptor mediated)
what products the vesicle
coat protein - clatherin
clatherin is a
coat protein
how does the vesicle know where to go
Rab protein
rab effector
moves vessicle to the plasma membrane
SNAREs
mediate fusion
v-snares
on the vesicle
t-snares
on the target membrane
