Lecture 2: Membrane Transport II Flashcards
define osmosis
Net movement of water across a semi-
permeable membrane caused
by a concentration difference of water
define osmolarity
equation?
how are osmolarity and permeability related
concentration of osmoticallly active particles in a solution
equation is n*concentration
osmolarity is inversely proportional to permeability
define osmotic pressure
the driving force on water due to solute concentration
reflection coefficient
number btwn 0 and 1 that describes ease of SOLUTE crossing through membrane (describes permeability
1 means not a chance for movement, like when channel is closed
define effective osmotic pressure
takes into account reflective coefficient and osmotic pressure (remember that osmolarity affects osmotic pressure)
hypertonic vs hypotonic vs isotonic and resulting effect
hypertonic means concentration on OUTSIDE or osmolarity is higher than inside of cell. the fore water flows out
hypotonic means concentration on INSIDE is greater than outside. therefore water flows inside
movement of water depends on
solute concentrations and aquaporins
where do you especially find aquaporins?
kidney tubules
what are the qualities of a carrier protein
(1) specificity: intermolecular forces bind to a specific ligand and release it when it crosses the membrane
(2) plateau: there is a plateau with the maximum amount of solute that can be transported. We don’t see this with SIMPLE DIFFUSION bc no saturation with simple diffusion
(3) Competition:
- ligand has affinity for carrier protein and they have competition to get to it. but carrier is also selective and has its favorites
- rmember that aa in pore governs charge and selectivity.
where are GLUT 2 vs GLUT 4 receptors found?
GLUT 2 in most cells, and is glucose sensor. pathway releases insulin**transporter for glucose to enter pancreatic beta cells
*both are transporters
GLUT4 in skeletal and cardiac muscle, fat, and are activated by insulin to bring it into the cell
the____ the Km, the higher the affinity
The lower the Km the higher the affinity.
clinical correlation to glut 4?
diabetes type II patients with insulin resistance can’t uptake insulin leading to hyperglycemia bc glucose not metabolized
which is entirely open from outter membrane to inner membrane? channel or transporter?
transporter is NEVER open entirely but
pore/channel is OPEN
clinical correlation of sodium/potassium ATPase?
how is inhibition of the pump a treatment?
cardiotonic steriods bind to an inhibit Na/K atpase.
these can be
-exogenous: from plants and amphibians
or
-endogenous: implicated in the development of hypertension including preclampsia
why can it be a treatment?
-keep sodium from depolarizing force for calcium release therefore keeping calcium in cell which is needed for heart.
done by digoxin.
describe the calcium ATPase pump
in 2 locations. remember that it pumps calcium against its gradient (therefore active tx)
1) plasma membrane: called PMCA or plasma membrane calcium ATPase which pumps calcium OUT
2) SERCA or sarcoendoplasmic reticulum calcium ATPase which pumps calcium IN.
remember that SERCA needs to pump Ca in,so the PMCA is opposite
describe the H/K atpase
clinical correlation?
moves H against gradient into LUMEN of stomach where ph is low. and K moves in
essentially an anti porter.
to remember direction- think about acidity. Want lumen to be more acidic so pump H that way
Proton pump inhibitors (omeprazole) are used to treat
gastroesophageal reflux disease,
gastric and duodenum ulcers and gastritis.
vesicular ATPases
Vesicular ATPases are located on membranes of intracellular organelles where they acidify these compartments by pumping H+ ions against a concentration gradient from the cytosol into the organelle.
ABC- primary transport
export xenobiotics - substances that are foreign to an organism or biological system
export cholesterol from cells – important for cholesterol homeostasis
export bile from the liver into digestive tract – important for digestion of lipids
called ATP binding Cassetes .these are EXPORTERS
other ABC that is nOT a transporter
1) CFTR: Cl- channel, not transporter. A regulated and gated channel (by P by regulatory substance). When ATP is bound and molecule Phosphorylated, selective Cl- channel.
explain cystic fibrosis
all about water movement needed for cilia to beat therefore
- when normal SODIUM INFLUX via Enac channels and CHLORIDE EFFLUX, via CFTR, then hydration of cilia which clears mucus
- but abnormal CFTR causes less fluid and increased mucus and secretory products
what is the Sulfonylurea Receptor
subunits of the K ATPase channel. help regulate the channel. target for diabetes drug
Na/glucose?
and clinical correlation?
where is it found?
Na+/glucose
cotransporter:
electrochemical gradient of Na+ is used to pump glucose against it’s electrochemical gradient.
*think g for gradient and glucose
- found in epithelial intestinal cells
- both sodium and glucose are osmotically active, therefore in diarrhea, it is fatal bc of water loss due to increased sodium in the LUMEN
tx: equal parts sodium and glucose to increase chance of sodium to bind to transporter
what is the NCX ? where is it found?
electrochemical gradient of Na used to pump Ca against its gradient.
3 sodiums for 1 calcium
sodium in
calcium out.
NCX is in the plasma membrane and does this antiport
if you increase cellular sodium, then you lower gradient. and get less calcium leaving the cel
which cells secrete insulin
pancreatic beta cells
omeprazole
H/K pump inhibitor to treat ulcers by lowering acidity of the lumen
