| How Things Get In/Out of
Cells
The Cell
Membrane...
1. Unit Membrane Hypothesis - "EM*
= all membranes look alike*"
photomicrographs: EM-neurons*
- 2. Source for study (plasma membrane - RBC ghosts)
-
RBC-bw,
RBC-color* and
RBC ghosts*
& SEM*
-
- Two Ways to Study Membranes & Transport of Solutes
Across Membranes
a.
NATURE OF MEMBRANE ITSELF
- "its
Molecular Makeup"
b.
PERMEABILITY STUDIES
- "Physiological Properties of
Membranes"
-
A. Current Molecular Model of Membrane Structure -
-
Fluid Mosaic model... has 2 major
molecular components
1.
lipids
= mostly
phospholipids*
&
cholesterol
-
lipid fluidity
- viscous vs. fluid (saturation vs. unsaturation)*
- 2.
proteins =
- a) Integral (intrinsic) proteins -
part of... & denatured
upon release from
b) Peripheral (extrinsic) - easily extractable
from membrane
Structural Models... (a historical
look at membrane structures)
-
Langmuir-troughs
Davson-Danielli model*
- Singer-Nicolson
model* glycoproteins secreted by cell
= a
cell "wall"
Fluid
Mosaic model* &
Extra-cellular Matrix*-common
to animal cells
-
- Functions of Membrane
Proteins*
-
Concept Activity -
chapter
7.1 -
Membrane Structure
end
B.
Physiological Properties of Membranes
Solute
Movement... since membrane is mostly lipid, movement of molecules
across- a membrane is based
upon lipid solubility (more lipid soluble
greater transport)
- -graph of
Partition
Coefficient vs. Permeability
-
actual
data and an
ideal
graph*
-
-
Water Movement... an anomaly
-
not lipid soluble, yet readily permeable
1.
Bulk flow... hydrodynamics or mass flow of water
-
due to potential energy of water (as in rivers & rapids)....
-
Water potential is the chemical/energy potential of water
& is a
measure of energy available for reactions or movement.
Water potential measures the ability of water to move.
"water
always moves from areas of high water potential to area of low potential".
-
-
-
-
-
-
-
-
-
-
-
-
-
2. Osmosis - net movement of water from [high Water Potential]
---> [low WP]
energy
required: passive transport of water, no energy required
osmosis*
SOLUTIONS - comparing one solution to
another solution
hypertonic solution = "more solute, less water" (hyperosmotic)
hypotonic solution = "less solute, more water"
(hypoosmotic)
isotonic solution = "equal solute and water" (isosmotic)
- Cells and
Solutions - plant vs.
animal and water balance
tonicity &
osmolality*
-
plasmolysis* - loss of cytoplasmic structure due to water loss
turgidity
- swollen cells due to water gain
Investigation - Process of Science - Chapter 7.3
-
How do salts Affect
Cells?
Concept Activity -
chapter 7.3 -
Osmosis and Water Balance
-
AQUAPORINS*
- Water Channel proteins (?)
2003 Nobel
Prize in Chemistry
-
-
-
-
-
- Membrane Solute Transport (ion or
molecule transport)
How Things
(solutes = molecules) Get Across a Membrane [4 Ways]
1. through a
PORE*...
made by
proteins embedded in bilayers*
allows ions &
small hydrophilics to move through [
a pore ]-
- 2. by
DISSOLVING IN*
membrane... hydrophobic solutes via lipid bilayer
-
-
3. by
CARRIER
PROTEINS* ...
proteins embedded
in membrane
w specificity for a solute
results in transport of solute through the protein by diffusion
- 4.
by membranes
ENGULFING
particles*
into membrane vesicles...
ENDOCYTOSIS - phagocytosis (forms
a phagosome - vesicle with solids)
&
& pinocytosis (forms
a liquid vesicle)
EXOCYTOSIS - export vesicles
[
figure*]
of endocytotic pathway
Membrane Transport
Concept Activity -
chapter 7.2 -
Selective Permeability of Membranes,
Concept Activity -
chapter 7.3 -
Diffusion
&
Osmosis
DIFFUSION*
- net thermal motion of solute
down a
concentration and/or electrical
gradient
...solutes move from area of higher to area of lower
concentration
-
is PASSIVE...
i.e., requires no expenditure of cellular energy
CARRIER MEDIATED
TRANSPORT... a special type of diffusion
also called
Facilitated Diffusion*
... ex:
Glucose Transport*
defined as protein mediated passive transport
Concept Activity -
chapter 7.3 -
Facilitated Diffusion
IONS? Nernst
Equation: defines
PASSIVE electrochemical quilibrium...
determines mathematically what the electrical potential (charge)
should
be across a cell based on existing
PASSIVE distribution of ions
E(mV) = (+/-) 62 log10 [Co/Ci]
flux equation*
K
ACTIVE TRANSPORT -
cells expends energy (often... splitting of ATP)
to move
a solute against a
concentration
gradient-
ex: animals-
Na-Pump* :
NaK-ATPase
plants-
Proton
Pump :
H+-ATPase*
-
both are
ELECTROGENIC... move
charge one way =
voltage
Concept Activity - Chapter 7.4 -
Active Transport
CO-TRANSPORT... movement of
2 solutes together -
often moves 1 solute passively & other actively
ex: 1) H+pump coupled with
sucrose transport (
H+symport*
)
2)
epithelial transport* Na+glucose
model (
glucose absorption* )
_______________________________________________________
definitions: uniport - single solute in one direction
symport - 2 solutes simultaneously in same
direction
antiport* - 1 solute in
& 1 solute out -opposite directions
-
-
Summary of passive
vs active transport*
______________________________________________________
-
-
-
-
Exocytosis
- releases
(out) bulk material
to outside...
fig
7.16*
Endocytosis ... takes
in
solutes/particles by vesicles
-
phagocytosis* -
solid
particle uptake into phagosome
vesicle
-
pinocytosis* -
liquid
uptake into pinocytotic
vesicle
-
receptor mediated*
endocytosis... uptake
@ membrane sites w receptors
- -
coated pits with protein clathrin
Sumanas, Inc. animation - Receptor Mediated
Endocytosis of cholesterol
Concept Activity -
chapter 7.5 -
Exocytosis and Endocytosis
both
 Key Concepts*
 animation of inner Life of Cell
- view @ home
go to next lecture on Cell Communication*
model organisms
- U of
Miami Home Page | Biology Home Page | Dr. Mallery's Home Page | On-Line Testing Center
- copyright c2005, Charles Mallery,
- Department of Biology, University of
Miami, Coral Gables, FL 33124
- Last Update -
08 October, 2009
Wiley Publishing animation of membrane transport
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