Lecture 9 Membrane Transport Flashcards Preview

Physiology > Lecture 9 Membrane Transport > Flashcards

Flashcards in Lecture 9 Membrane Transport Deck (43)
Loading flashcards...
1

Permeability

ability of a substance to pass through a membrane

2

What is permeability determined by?

the phospholipid bilayer
membrane transport proteins

3

Molecular size

smaller molecules are more permeable

4

Lipid solubility

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)

5

Membrane transport proteins

help ions and molar molecules to pass through

6

Highly permeable

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

7

less permeable

Na+, K+, Cl- (via channels)
glucose, a.a's (via carriers)

8

Impermeable

proteins (except via vesicles)
ATP
DNA, RNA

9

Passive Transport

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

10

Active Transport

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

11

Protein mediated transport

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

12

Simple Diffusion

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

13

Fick's Law of diffusion

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)

14

Osmosis

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)

15

Osmolarity

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

Non-ionic solutes and salts

16

Non-ionic solutes

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

17

Salts

ionize in H20
1M NaCl -> 1M Na+ + 1M Cl- = 2 Osm

18

Osmotic pressure

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

19

Tonicity

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

20

Hypertonic
Hypotonic
Isotonic

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

21

Diffusion through Channels

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

22

Aquaporins

water channels found in most cell membranes

23

Electrochemical gradient

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

24

Facilitated Diffusion

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

25

GLUT proteins

Facilitated Diffusion

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

26

GLUT4

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

27

Primary Active Transport

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

28

Na+/K+ Pump

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

29

Other active transport pumps

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

30

Secondary Active transport

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