Download Membrane Structure and Function

Membrane Structure
and Function
Topic 3
Plasma Membrane Functions
Maintain a high concentration of materials in the cell.
Keep harmful materials out.
Control the movement of materials into and out of the cell.
Let the cell sense its
environment.
Membrane Structure
Phospholipid
bilayer
Amphipathic
“liquid-crystal”
properties/behavior allow for
constant movement of HC tails
The Plasma Membrane is Semipermeable
Davson-Danielli vs. Fluid Mosaic
Membrane Characteristics
 “self-sealing”
 Flexible
 Tend
to form vesicles
(ENDOCYTOSIS)
 Tend to fuse w/ other bilayers
(EXOCYTOSIS)
LIPID MOBILITY
http://www.d.umn.edu/~sdowning/Membranes/phospholipidlat
eralmovanim.html
http://www.d.umn.edu/~sdowning/Membranes/phospholipidrotation
alanim.html
Relationships w/ other
intracellular membranes
Nuclear
Memb.
Rough
ER
vesicles
Golgi Bodies
lysosomes &
vacuoles
vesicles
cell memb
MEMBRANE PROTEINS

Integral Proteins:
Anchored into membrane
Transmembrane
proteins
Peripheral
Proteins
no anchoring to membrane
often bound to exposed regions
of integral proteins
PROTEIN MOBILITY
http://www.d.umn.edu/~sdowning/Membra
nes/proteinmobilityanim.html
Proteins Are Critical to Membrane Function
Membrane Protein Functions

Cell Adhesion
 Communication
Channels
 Transport Channels
 Signal Receptors btwn.
Ext/Int cell
 Attachment Sites
 Pumps
 Enzymes

Peripheral
 Integral

Integral
 Integral

Peripheral
 Integral
 Both
Protein Signaling
http://www.d.umn.edu/~sdowning/Membranes/signalinga
nim.html
Membrane Components
Phospholipids
Proteins (peripheral and integral)
Cholesterol
Carbohydrates
The Plasma Membrane – Gateway to the Cell
MOVEMENT ACROSS THE
CELL MEMBRANE
Transport Processes - Diffusion
Solutes move
down a
concentration
gradient until they
are evenly
distributed. This
is diffusion.
Another way of saying this is that solutes move from a region of higher
concentration to a region of lower concentration until there is no difference
in concentration.
Methods of Movement
PASSIVE
TRANSPORT
DIFFUSION
SIMPLE DIFFUSION
 OSMOSIS
 FACILITATED DIFFUSION

Three Forms of Transport Across the Membrane
ACTIVE
TRANSPORT
PUMPS
EXOCYTOSIS
ENDOCYTOSIS
PHAGOCYTOSIS
 PINOCYTOSIS
 RECEPTOR-MEDIATED

DIFFUSION
Cell
obtains / releases
substances by taking
advantage of natural properties
of movement (kinetic E)!
Diffusion is…
NET
movement of mcls from
[ ]
[ ]
Down the [ ] gradient : . NO
Energy required.
Rate of Diffusion influenced by:
Size
/ shape of molecules
moving
Electrical charges across
membrane
Temperature (
= movement,
:.
Diffusion )
Substances
diffuse down their
own [ ] gradient…
NOT affected by [ ] gradient of
other substances !!
Diffusion continues until…
Dynamic
Equilibrium
is
reached!
OSMOSIS
Diffusion
of water across the
semi-permeable plasma
membrane.
Water moves down its own [ ]
gradient.
* Zones of Hydration
Spheres of Hydration
Osmotic Pressure

tendency of water to move into a
solution by osmosis.
High [solute] = low [water]
High Osmotic Pressure
Comparing Solutions:
HYPOTONIC :
refers to the less concentrated
(more dilute) of two solutions.
HYPERTONIC :
refers to the more concentrated
(less dilute) of two solutions.
If
a cell is placed in a hypotonic
solution, the cell will….
S W E L L and
B U R S T !!
Turgidity issues…
If a cell is placed in a hypertonic
solution, the cell will…
S H R I N
(CRENATION)
K !
ISOTONIC :
refers to two solutions where there
is no net movement of water
between the two.
a cell is placed in an isotonic
solution, there will be….
no net movement of water
into / out of the cell.
The Problem of
Osmotic Pressure
What’s the risk?
How can osmotic pressure be
minimized?
 Live
in an
isotonic
enviroment
 Contractile
vacuoles
 plasmolysis
Marine
invertebrates
Human RBC’s
Unicellular
protists
Plant cells
Contractile Vacuoles
Plasmolysis… Cell Wall Action
Transport Problems ?
 CYSTIC
FIBROSIS
 LIDDLE’S SYNDROME