Lecture 2: Membrane Transport II

Question 1

define osmosis

Answer 1

Net movement of water across a semi-
permeable membrane caused
by a concentration difference of water

Question 2

define osmolarity
equation?
how are osmolarity and permeability related

Answer 2

concentration of osmoticallly active particles in a solution
equation is n*concentration

osmolarity is inversely proportional to permeability

Question 3

define osmotic pressure

Answer 3

the driving force on water due to solute concentration

Question 4

reflection coefficient

Answer 4

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

Question 5

define effective osmotic pressure

Answer 5

takes into account reflective coefficient and osmotic pressure (remember that osmolarity affects osmotic pressure)

Question 6

hypertonic vs hypotonic vs isotonic and resulting effect

Answer 6

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

Question 7

movement of water depends on

Answer 7

solute concentrations and aquaporins

Question 8

where do you especially find aquaporins?

Answer 8

kidney tubules

Question 9

what are the qualities of a carrier protein

Answer 9

(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.

Question 10

where are GLUT 2 vs GLUT 4 receptors found?

Answer 10

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

Question 11

the____ the Km, the higher the affinity

Answer 11

The lower the Km the higher the affinity.

Question 12

clinical correlation to glut 4?

Answer 12

diabetes type II patients with insulin resistance can’t uptake insulin leading to hyperglycemia bc glucose not metabolized

Question 13

which is entirely open from outter membrane to inner membrane? channel or transporter?

Answer 13

transporter is NEVER open entirely but

pore/channel is OPEN

Question 14

clinical correlation of sodium/potassium ATPase?

how is inhibition of the pump a treatment?

Answer 14

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.

Question 15

describe the calcium ATPase pump

Answer 15

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

Question 16

describe the H/K atpase

clinical correlation?

Answer 16

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.

Question 17

vesicular ATPases

Answer 17

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.

Question 18

ABC- primary transport

Answer 18

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

Question 19

other ABC that is nOT a transporter

Answer 19

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.

Question 20

explain cystic fibrosis

Answer 20

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

Question 21

what is the Sulfonylurea Receptor

Answer 21

subunits of the K ATPase channel. help regulate the channel. target for diabetes drug

Question 22

Na/glucose?
and clinical correlation?
where is it found?

Answer 22

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

Question 23

what is the NCX ? where is it found?

Answer 23

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

Question 24

which cells secrete insulin

Answer 24

pancreatic beta cells

Question 25

omeprazole

Answer 25

H/K pump inhibitor to treat ulcers by lowering acidity of the lumen