Sullivan General Human Physiology Lecture 5

Front 1

Movement across membranes
- general

Back 1

* plasma membrane is selectively permeable
* therefore concentration differences exist between extracellular and intracellular compartments

Front 2

Movement across membranes:
Mechanisms

Back 2

1. Diffusion
2. Mediated transport
a. facilitated diffusion
b. active transport
i. primary
ii. secondary
3. Osmosis

Front 3

Diffusion:
- general

Back 3

redistribution of molecules from a region of high concentration to a region of low concentration
* molecules move
* random collisions
* FLUX is the amount of material crossing a surface in unit time
* NET FLUX is the DIFFERENCE between 2 opposing, 1way fluxes
-----A----->
<--B--
NET FLUX = A-B

Front 4

In diffusion NET FLUX is always from ...

Back 4

HIGH concentration to LOW

Front 5

Diffusion:

NET FLUX (proportional to)

Back 5

* concentration difference
* size of surface area
* membrane permeability constant (KP)

Front 6

Diffusion:

KP (membrane permeability constant) based on:

Back 6

* type of molecule
* molecular weight
* temperature
* characteristics of membrane

Front 7

DIFFUSION thru a CELL MEMBRANE can be thru:

Back 7

* can be thru phospholipid bilayer
* can be thru channels (pores)

Front 8

Diffusin THRU THE PHOSPHOLIPID BILAYER:

Back 8

* polar molecules diffuse into cells slowly/or not at all
* nonpolar molecules (O2, CO2, fatty acids and steroids) diffuse rapidly because they readily dissolve in fatty acid chains (nonpolar portions) of membrane phospholipid

Front 9

diffusion THRU PROTEINS CHANNELS

Back 9

* Na+, K+, Cl-, Ca++
* integral proteins span lipid bilayer forming channels thru which these ions diffuse
* ion channels are slective for ion type (according to)
1. diameter
2. charged/polar surfaces of protein channel (attract/repel ions)

Front 10

what FORCES also effect the diffusion of ions?

Back 10

ELECTRICAL FORCES acting on ions also effect their diffusion

Front 11

Membrane Potential:
General

Back 11

* a separation of electrical charge across a membrane
*** If the inside of a cell(-) there will be an electrical force attracting (+) ions into the cell and repelling (-) ions.
* membrane permeability to ions can be altered by channel gating (opening/closing channels)

Front 12

Membrane Potential:
* the DIRECTION AND MAGNITUDE of ion flux thru a channel, across a membrane will depend on:

Back 12

1. concentration difference
2. membrane potential (electrical difference)

Front 13

Membrane Potential:
* MAGNITUDE (number of ions) that pass thru channel will depend on:

Back 13

1. frequency of channel opening
2. duration of channel opening

Front 14

Channel Conformation
(whether open/closed)
can be altered ...

Back 14

3 ways:
1. RECEPTOR OPERATED CHANNELS
(open/close when a specific CHEMICAL binds to receptor)
2. VOLTAGE-SENSITIVE CHANNELS
(open/close when membrane electrical potential is altered)
3. STRETCH-ACTIVATED CHANNELS
(open/close when smooth muscle cells are stretched)

Front 15

Mediated Transport

Back 15

* needed to move substances TOO POLAR to diffuse thru the lipid bilayer or TOO BIG to diffuse thru protein channels
* movement of these ions MEDIATED by CARRIERS
* carriers are integral proteins

Front 16

General Mechanism of Mediated Transport

Back 16

1. Substance BINDS to specific site on a carrier (on membrane surface)
2. Carrier protein CHANGES SHAPE, exposing its binding site to opposite side of membrane
3. DISSOCIATION of substance from carrier binding site

Front 17

Magnitude of mediated transport is proportional to:

Back 17

1. saturation of carrier
2. number of carrier proteins in membrane

Front 18

Types of Carrier-Mediated Transport:

Back 18

2 Types:
1. Facilitated Diffusion
2. Active Transport

Front 19

Facilitated Diffusion

Back 19

* moves solute from HIGH TO LOW concentration across membrane
* does NOT involve diffusion
* does NOT require energy
* when carrier changes shape so that binding site goes from facing surface to facing other side binding properties of site DO NOT CHANGE
* binding determined by concentration difference
ie: glucose moves into cell (large/polar) across cell membrane by facilitated diffusion
- glucose metabolized immediately inside cell so .. concentration always LOW inside cell

Front 20

Active Transport

Back 20

* uses energy
* transport uphill
* called active transport "pumps"
* ion flux (depends on electrical difference/concentration)
* uses carrier-proteins
* maximum flux when binding sites are saturated
* some pump into cells
some pump out of cells

Front 21

Active Transport:
Carriers

Back 21

* carrier CHANGES SHAPE so binding site accessible first on one side/then to molecules on other side.
* CARRIERS HAVE BINDING SITES THAT DIFFER IN AFFINITY ON OPPOSITE SIDES OF MEMBRANE

Front 22

Active Transport:
Affinity

Back 22

* CARRIERS HAVE BINDING SITES THAT DIFFER IN AFFINITY ON OPPOSITE SIDES OF MEMBRANE
* direction of transport depends on which side has low affinity binding site (moves from high affinity side to low affinity side)
differnce in affinity produced by ENERGY (ATP)

Front 23

PRIMARY Active Transport

Back 23

* uses ATP directly
* chemical energy from ATP transferred to carrier
* carrier protein acts as an enzyme (ATPase) and catalyzes its own phosphorylation
(phosphorylation of carrier at one binding site alters affinity of solute binding site at different point on carrier)
* COVALENT MODULATION
* phosphorylation/dephosphorylation produces binding sites of differing affinities

Front 24

primary active transport carriers

Back 24

4 primary active transport carriers
1. Na/K ATPase carrier
2. Ca ATPase carrier
3. H ATPase carrier

Front 25

SECONDARY Active Transport

Back 25

* uses ion concentration
* flow of some ion from high concentration to low concentration provides energy for uphill transport of solute
* binding of ion (Na+, HCO3-, Cl-, K+) to carrier alters affinity of other site for transporting solute or altering rate at which carrier moves binding site from one side to other (transport)
* carrier has 2 binding sites (1 for solute being transported/1 for ion)
* ALLOSTERIC MODULATION
ie: amino acids are transported this way

Front 26

Components needed for OSMOSIS to occur:

Back 26

1. H2O
2. a membrane
3. a nonpenetrating solute
4. a concentration difference

Front 27

Osmosis

Back 27

* net diffusion of H2O from a region of high concentration of water to a region of low concentration of water
* adding solute to water lowers the concentration of H2O
* the more solute present... the less water (higher solute concentration/lower water concentration)
* water flows toward solutions of higher solute concentration, since such solutions have lower H2O concentration
** a molecule that IONIZES in solution decreases the water concentration in proportion to the number of ions formed

Front 28

Osmosis illustration

Back 28

1 mole NaCl <=====> 1 mole Na+ + 1 mole Cl-
(2 moles of particles)

1 mole glucose <=====> 1 mole glucose
(1 mole of particles)

Front 29

OSMOTIC PRESSURE

Back 29

If a solution contains nonpenetrating solute, separated from pure H2O by a membrane, the pressure that must be applied to prevent a net flow of H2O across the membrane (from the pure H2O side to the nonpenetrating solute side) is called OSMOTIC PRESSURE

Front 30

ISOTONIC SOLUTIONS

Back 30

2 solutions that each contain equal concentrations of nonpenetrating solute
(also equal concentrations of H2O)

Front 31

HYPOTONIC SOLUTION

Back 31

a solution that contains less nonpenetrating solute than the solution to which it is being compared (also more H2O)

Front 32

HYPERTONIC SOLUTION

Back 32

a solution that contains more nonpenetrating solute than the solution to which it is being compared
(also less H2O)