Download Animal cells

Cell Membrane & Cell
Transport
About Cell Membranes*
1.All cells have a cell
membrane
2.Functions:
a.Controls what enters
and exits the cell to
maintain an internal
balance called
homeostasis
b.Provides protection and
support for the cell
TEM picture
of a real cell
membrane.
Cell Membranes are made of a
PHOSPHOLIPID bilayer which is
Amphipathic –
Molecules with
both hydrophilic
and hydrophobic regions
phosphate
hydrophilic
lipid
hydrophobic
PHOBIC TAILS in center determine
what can pass through
*More than just a barrier…
• Expanding our view of cell membrane
beyond just a phospholipid bilayer barrier
– phospholipids plus…
*A membrane is a collage of different proteins
& carbohydrates & cholesterol embedded in
the fluid matrix of the lipid bilayer
Polar heads *Fluid Mosaic
love water
Model of the
& dissolve. cell membrane
Non-polar
tails hide
from water.
Carbohydrate cell
markers
Proteins
Membrane
movement
animation
Membrane Proteins
• Proteins determine most of membrane’s specific
functions
– cell membrane & organelle membranes each have
unique collections of proteins
• Membrane proteins:
– peripheral proteins = loosely
bound to surface of membrane
– integral proteins = penetrate into
lipid bilayer, often completely
spanning the membrane =
transmembrane protein
Membrane Carbohydrates
• Attached to proteins (glycoproteins)
or lipids (glycolipids)
• Play a key role in cell-cell recognition
– ability of a cell to distinguish neighboring cells
from another
– important in organ &
tissue development
– basis for rejection of
foreign cells by
immune system
http://faculty.southwest.tn.edu/rburkett/GB1-osmosis.htm
Types of Cellular Transport
•
1. Diffusion
2. Facilitated Diffusion
3. Osmosis
•
Wee!!!
Passive Transport
cell doesn’t use energy
Active Transport
cell does use energy
1. Protein Pumps
2. Endocytosis
3. Exocytosis
high
low
This is
gonna
be hard
work!!
high
low
*Molecules need to move across
membranes in cells
OUT
waste
ammonia
salts
CO2
H2O
products
IN
food
carbohydrates
sugars,
proteins
amino acids
lipids
salts, O2, H2O
Image modiified from: http://www.accessexcellence.org/AB/GG/importProt.html
*Diffusion: movement directly through
membrane. What molecules can get
through directly?
Small non-polar molecules (O2 & CO2) and
hydrophobic molecules (fats & other lipids)
can slip directly
lipid O2
inside cell
through the
salt
NH3
phospholipid cell
membrane, but…
outside cell sugar aa
H 2O
What about
other stuff?
Diffusion
• Passive transport
– No energy needed
• High to low concentration
• Small, nonpolar molecules
• Continues until equilibrium and then
moves randomly
*Diffusion
• 2nd Law of Thermodynamics
governs biological systems
– Universe tends towards disorder
Animatioin from: http://www.biologycorner.com/resources/diffusion-animated.gif
• Diffusion
– movement from [higher]  [lower] concentration
*Diffusion will
also happen
across a cell
membrane as long
as there is a
difference in
concentration and
the membrane will
let the molecule
pass through until
equilibrium and
then moves
randomly
The Special Case of Water
Movement of water across
the cell membrane =
OSMOSIS
Osmosis is diffusion of water
• Water is very important, so we talk about
water separately
• Diffusion of water from high concentration
of water to low concentration of water
– across a
semi-permeable
membrane
– Passive
– Uses no energy
Concentration of water
• Direction of osmosis is determined by
comparing total solute concentrations
– Hypertonic - more solute, less water
– Hypotonic - less solute, more water
– Isotonic - equal solute, equal water
water
hypotonic
hypertonic
net movement of water
Solute concentration
Lower outside
than inside
Equal outside
and inside
Greater outside
than inside
HYPOTONIC
ISOTONIC
HYPERTONIC
What will happen to an animal cell
placed in different solutions?
*How Organisms Deal
with Osmotic Pressure
•Bacteria and plants have cell walls that prevent them
from over-expanding. In plants the pressure exerted on
the cell wall is called tugor pressure.
•A protist like paramecium has contractile vacuoles that
collect water flowing in and pump it out to prevent them
from over-expanding.
•Salt water fish pump salt out of their specialized gills so
they do not dehydrate.
•Animal cells are bathed in blood. Kidneys keep the
blood isotonic by remove excess salt and water.
*Grocery stores spray water on
their veggies to “plump them up”
http://www.painetworks.com/photos/gt/gt0461.JPG
Animal cells
= CYTOLYSIS
= CRENATION
http://www.stchs.org/science/courses/sbioa/metenergy/bloodcells.gif
http://www.stchs.org/science/courses/sbioa/metenergy/aplantturgor.gif
Plant cells
Cell wall keeps
plant cell from bursting
= PLASMOLYSIS
http://www.biology4kids.com/files/cell_vacuole.html
*Loss of water from central vacuole= plants “wilt”
Vacuole full of water gives plant support
(turgor pressure)
Turgid = very firm
Flaccid = limp
*Managing water balance
• Isotonic
– animal cell immersed in isotonic
solution
• blood cells in blood
• no net movement of water across
plasma membrane
• water flows across membrane, at
same rate in both directions
• volume of cell is stable
Facilitated diffusion
• Move from HIGH to LOW concentration with
aid of membrane transport proteins
– passive transport
• no energy needed
– facilitated = with help
– Medium size molecules;
monomers
Ion Channels
Move from HIGH to LOW concentration with aid of
membrane transport proteins
- passive transport
- no energy needed
- facilitated = with help
- Small, charged molecules
*Carriers and Channels are specific
inside cell
H2O
aa
sugar
NH3
salt
outside cell
. . . BUT STILL MOVES FROM [HIGHER] to [LOWER]
Active transport
Uses energy from ATP to move molecules
against concentration gradient
– Moves from [lower] → [higher]
– Uses protein pumps
OR
vesicles
Animations from:
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/cell-movement.html
http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/eustruct/images/sppump.gif
Active transport
SODIUM-POTASSIUM PUMP
Sets up difference in charge across membranes
Pumps 3 Na+ out
and 2 K+ in
Makes cells
more + outside
more - inside
Animation from: http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/eustruct/images/sppump.gif
*BULK TRANSPORT
• ACTIVE transport
– Requires energy (ATP)
• Uses vesicles
Animation from: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBooktransp.html
Endocytosis
phagocytosis
pinocytosis
receptor-mediated
endocytosis
“Cell eating”
large molecules;
whole cells
“Cell drinking”
Fluids;
Small molecules
triggered by
ligand signal
*PHAGOCYTOSIS
Animation from: http://academic.brooklyn.cuny.edu/biology/bio4fv/page/cell-movement.html
“Cell eating”
takes in
large molecules;
whole cells
See phagocytosis
in action:
http://www.accs.net/users/kriel/chapter%20nine/
*Example in cells:
WHITE BLOOD CELL ENGULFING
BACTERIA using Phagocytosis
http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x28.jpg
*PINOCYTOSIS
“Cell drinking”
Takes in fluids;
Small molecules
http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/pinocyt.html
EXOCYTOSIS
• Active transport (requires ATP)
• Uses vesicles
• Releases substances to outside
INSULIN being released by pancreas cells using exocytosis
Video: http://www.southtexascollege.edu/tdehne/BC_ShockwaveAnimations/07SWF-TourOfTheCell/07-16-EndomembraneSystem.swf
*GOLGI BODIES USE
EXOCYTOSIS
Animation from: http://www.franklincollege.edu/bioweb/A&Pfiles/week04.html
*Transport summary
*PROBLEM for
Cells?
Cell membranes
are
SELECTIVELY
PERMEABLE