Lecture 9 Membrane Transport

Question 1

Permeability

Answer 1

ability of a substance to pass through a membrane

Question 2

What is permeability determined by?

Answer 2

the phospholipid bilayer

membrane transport proteins

Question 3

Molecular size

Answer 3

smaller molecules are more permeable

Question 4

Lipid solubility

Answer 4

non-polar molecules are lipid soluble meaning they are more permeable (ex: fatty acids)

polar molecules and ions are less permeable or impermeable (ex: H2O)

Question 5

Membrane transport proteins

Answer 5

help ions and molar molecules to pass through

Question 6

Highly permeable

Answer 6

02 & C02
Fatty acids
steroids
H20 (variable: pores)

Question 7

less permeable

Answer 7

Na+, K+, Cl- (via channels)

glucose, a.a’s (via carriers)

Question 8

Impermeable

Answer 8

proteins (except via vesicles)
ATP
DNA, RNA

Question 9

Passive Transport

Answer 9

does not require energy
substances move down gradient
Simple diffusion, osmosis, diffusion through channels, facilitated diffusion

Question 10

Active Transport

Answer 10

requires energy
transport against gradient
primary active transport, secondary active transport, transport via vesicles (endocytosis, exocytosis)

Question 11

Protein mediated transport

Answer 11

diffusion through channels, facilitated diffusion, primary active transport, secondary active transport

Question 12

Simple Diffusion

Answer 12

results from random molecular motion
net movement from high concentration to low concentration
Fick’s Law of diffusion

Question 13

Fick’s Law of diffusion

Answer 13

gives the rate of diffusion
Rate=P A (Cout-Cin) / X
rate is proportional to permeability (P), surface area (A), concentration gradient (Cout-Cin)
inversely proportional to diffusion distance or membrane thickness (x)

Question 14

Osmosis

Answer 14

passive movement of water across a membrane due to solute concentration difference
permeable to H20 but impermeable to solutes
primary mechanism for H20 transport across membranes
H20 ,moves from dilute to concentrated solution (solutes suck water)

Question 15

Osmolarity

Answer 15

total concentration of all solutes in a solution
1 Osm = 1 mole of solutes per liter

Non-ionic solutes and salts

Question 16

Non-ionic solutes

Answer 16

osmolarity = concentration

e.g. 1 M glucose = 1 Osm = 1,000 mOsm

Question 17

Salts

Answer 17

ionize in H20

1M NaCl -> 1M Na+ + 1M Cl- = 2 Osm

Question 18

Osmotic pressure

Answer 18

driving force for osmosis
depends on difference in total solute concentration
negative pressure pills water from dilute to concentrated solution

Question 19

Tonicity

Answer 19

effect of an extracellular solution on cell volume, due to H20 movement by osmosis

Question 20

Hypertonic
Hypotonic
Isotonic

Answer 20

hypo - H20 moves in cell expands
hyper - H20 moves out cell shrinks
Iso- no net movement of H20 cell volume stays constant

Question 21

Diffusion through Channels

Answer 21

Ion channels are protein passageways for ions through the membrane
most channels are selective for certain ions
ions diffuse down electrochemical gradients
channels may be ungated or gated

Question 22

Aquaporins

Answer 22

water channels found in most cell membranes

Question 23

Electrochemical gradient

Answer 23

combination of concentration and electrical gradients
can act in same direction ( Na+)
or in opposite direction (K+)

Question 24

Facilitated Diffusion

Answer 24

carrier proteins mediate diffusion of certain polar molecules across the membrane
down concentration gradient, no energy required
each carrier is specific to particular molecules
saturation- rate limited by number of carrier proteins in the membrane

Question 25

GLUT proteins

Answer 25

Facilitated Diffusion family of glucose transporters, present in many call membranes most body cells take up glucose by FD using GLUT proteins

Question 26

GLUT4

Answer 26

activated by insulin is the insulin dependent glucose carrier of skeletal muscle, adipose tissue, liver, and connective tissue Insulin promotes insertion of GLUT4 into the membrane -> glucose uptake via FD

Question 27

Primary Active Transport

Answer 27

pumps are transport proteins that use energy from ATP directly transport ions "uphill" against electrochemical gradients

Question 28

Na+/K+ Pump

Answer 28

Transports Na+ OUT and K+ IN maintains ionic composition of ICF and ECF K+ and Na+ gradients are the basis of electrical properties of cells Na+ gradient provides potential energy for transport of other molecules Na+/K+ pump activity is stimulated by THYROID hormones

Question 29

Other active transport pumps

Answer 29

Ca2+ -ATPase in muscles | H+ - ATPase in stomach

Question 30

Secondary Active transport

Answer 30

uses potential energy stored in IONIC gradients to move other molecules transport protein couples "downhill" flow of an ion to uphill transport of another molecule

Question 31

Cotransport

Answer 31

SAT | movement of both molecules in the same direction

Question 32

countertransport

Answer 32

SAT | movement in opposite directions

Question 33

SGLT

Answer 33

SAT is a Na+-glucose cotransporter in the small intestine and kidney epithelium moves glucose against its gradient from the lumen into the epithelial cell uses energy contained in the Na+ gradient

Question 34

Endocytosis

Answer 34

phagocytosis | pinocytosis

Question 35

Exocytosis

Answer 35

secretion of products out of the cell (mucus, neurotransmitters, hormones) also functions for insertion of molecules into the plasma membrane (lipids, proteins)

Question 36

Epithelial Transport

Answer 36

From lumen to ICF to ECF

Question 37

Apical membrane

Answer 37

faces lumen | microvilli increase surface area (ficks law)

Question 38

Basolateral membrane

Answer 38

faces ECF, attached to basement membrane | contains Na+/K+ pumps

Question 39

Tight Junctions

Answer 39

join epithelial cells, near apical surface, prevent fluid leakage between cells

Question 40

Transepithelial Transport

Answer 40

NaCl, glucose and H20 in the small intestines and kidneys

Question 41

NaCl | transepithelial transport

Answer 41

apical membrane: Na+ enters via diffusion through channels basolateral membrane: primary active transport (Na+/K+ pump) moves Na+ out to ECF Cl- follows Na+ passively by diffusion through channels

Question 42

Glucose | transepithelial transport

Answer 42

apical membrane: secondary active transport - cotransport with Na+ (SGLT) basolateral membrane: faciliated diffusion of glucose out to ECF (GLUT)

Question 43

Water | Transepithelial transport

Answer 43

moves by osmosis across apical and basolateral membranes; follows solute movement pumping of Na+ to ECF between cells promotes H20 movement by osmosis