Cell Membranes are made of PHOSPHOLIPIDS & PROTEINS
Amphipathic Molecules with both hydrophilic and hydrophobic regions
phosphate lipid hydrophilic hydrophobic
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FLUID MOSAIC MODEL 1972- S.J. Singer and G. Nicolson propose
membrane is a mosaic of proteins and phospholipids that are
constantly moving and changing Click here to See Fluidity Animation
from: http://www.sp.uconn.edu/~terry/images/anim/fluidmem.gif Click
here to See FLUIDITY
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More than just a barrier Expanding our view of cell membrane
beyond just a phospholipid bilayer barrier phospholipids plus
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2.4.2 Cell Membrane Micrograph
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A membrane is a collage of different proteins embedded in the
fluid matrix of the lipid bilayer
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2.4.1 Structures in Cell Membrane (animation)
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Membrane Proteins Proteins determine most of membranes specific
functions enzymes, receptors and transport Membrane proteins:
peripheral proteins = loosely bound to surface of membrane integral
proteins = penetrate into lipid bilayer, often completely spanning
the membrane = transmembrane protein
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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
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HYDROPHILIC/HYDROPHOBIC areas determine positions of molecules
in cell membranes hydrophobic amino acids stick in the lipid
membrane anchors the protein in membrane hydrophilic amino acids
stick out in the watery fluid in or out of cell
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Glycocalyx Fuzzy, sticky carbohydrate rich substance at the
cell surface. aid in cell communication gives support to cell
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Cell Junctions Most cells live in tight knit communities (but
some are Footloose) 3 factors act to bind cells together
Glycoproteins in glycocalyx Contours fit together in
tongue-and-groove fashion Special cell junctions
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Tight Junctions Series of proteins in cellular membrane which
fuse together Impermeable junctions nothing can pass between the
cells
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Desmosomes Anchoring junction connections between cells that
prevent cells from separating.
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Gap Junctions Communicating junction between cells. Adjacent
plasma membranes are very close and the cells are connected by
hollow cylinders
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Membranes provide a variety of cell functions
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Semi-permeable membrane Need to allow passage through the
membrane But need to control what gets in or out membrane needs to
be semi-permeable aa H2OH2O sugarlipidsalt NH 3 So what makes a
membrane semi permeable? See a movie
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PHOBIC TAILS in center determine what can pass through
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Molecules need to move across membranes in cells Image
modiified from:
http://www.accessexcellence.org/AB/GG/importProt.html IN food
carbohydrates sugars, proteins amino acids lipids salts, O 2, H 2 O
OUT waste ammonia salts CO 2 H 2 O products
Slide 21
What molecules can get through directly? inside cell outside
cell Small non-polar molar molecules (O 2 & CO 2 ) and
hydrophobic molecules (fats & other lipids) can slip directly
through the phospholipid cell membrane, but lipid salt aa H2OH2O
sugar NH 3 O2O2 What about other stuff?
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2.4.4 Diffusion Diffusion is the passive movement of particles
form a region of high concentration to a region of low
concentration Molecules of dye Membrane (cross section) Net
diffusion Equilibrium Net diffusion Equilibrium
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http://www.le.ac.uk/pa/teach/va/anatomy/case2/2_2.html Example:
DIFFUSION IN CELLS O 2 automatically moves from HIGHER
concentration (in lungs) to LOWER concentration (in blood) CO 2
automatically moves from HIGHER concentration (in blood) to LOWER
concentration (in lungs)
http://facstaff.bloomu.edu/gdavis/links%20100.htm
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2.4.4 Osmosis is the passive movement of water molecules across
a permeable membrane from lower solute to higher solute
concentration Hypotonic = lower [solute] Hypertonic = higher
[solute] Isotonic = equal [solute] Hypo -> Hypertonic
Osmosis
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Lower concentration of solute (sugar) Higher concentration of
sugar Same concentration of sugar Selectively permeable mem- brane:
sugar mole- cules cannot pass through pores, but water molecules
can More free water molecules (higher concentration) Water
molecules cluster around sugar molecules Fewer free water molecules
(lower concentration) Water moves from an area of higher free water
concentration to an area of lower free water concentration Osmosis
2.4.4
2.4.5 Simple diffusion is the tendency of molecules of a
substance to spread out evenly in an available space. Substances
diffuse down their gradient (high to low concentration). Small,
non-ionic, non-polar particles are able to pass through the
phospholipids is the membrane is permeable to them.
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Facilitated diffusion Move from HIGH to LOW concentration with
aid of membrane transport proteins passive transport no energy
needed facilitated = with help
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2.4.5 Facilitated diffusion is the movement of molecules across
a membrane with the aid of channel proteins. Channel proteins
create a bridge for particles to cross between the membrane. Their
size and chemical properties makes them specific to one
molecule.
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Carriers and Channels are specific inside cell outside cell
sugaraa H2OH2O salt NH 3... BUT STILL MOVES FROM [HIGHER] to
[LOWER]
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What if cell needs to move a molecule _________ the
CONCENTRATION GRADIENT? _______________ Cell example: Want to put
MORE glucose into mitochondria when there is already glucose in
there (LOWER HIGHER) Image from:
http://www.biologyclass.net/mitochondria.jpg AGAINST
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What if a cell needs to move _____ or ______ molecules that
cant get through the membrane?
http://www.d.umn.edu/~sdowning/Membranes/membraneImages/jpegimages/diffusionmedium.jpg
LARGEPOLAR
Slide 34
What if cell needs to move molecules really _______? (cant wait
for it to diffuse) Cell example: Movement of Na + & K + ions
required to send nerve signals
http://www.steve.gb.com/images/science/neuron.png FAST
Slide 35
Cells need a ____ to ____ molecules across cell membranes that
_______ across by ___________ WAY HELP cant go themselves
Slide 36
2.4.6 Active transport involves moving substances AGAINST their
concentration gradients (from low to high concentration). This is
done by protein pumps embedded in the membrane. In contrast to
passive transport, active transport requires energy in the form of
ATP.
Slide 37
2.4.6 Active Transport with ATP
Slide 38
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
See a movie See a movie about Na+ - K+ pump
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2.4.6
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2.4.7 Vesicles can be to used to transport materials within the
cytoplasm of the cell without mixing their components. They are
small sacs of membrane that can change shape and move in and out of
the cell Made in the rough Endoplasmic Reticulum by pinching off
small regions of membrane ATP supplies energy
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2.4.7 Transmembrane glycoproteins Secretory protein Glycolipid
Golgi apparatus Vesicle Transmembrane glycoprotein Membrane
glycolipid Plasma membrane: Cytoplasmic face Extracellular face
Secreted protein 4 1 2 3 Their membranes are made by the rough
Endoplasmic Reticulum, which later merge with the plasma membrane
via fusion. Membrane carbohydrates / lipids that are synthesized in
the rER are modified in the Golgi apparatus
Slide 45
2.4.7 Important Steps for Vesicles 1.Move material around in
cell 2. Protein is synthesized by ribosomes on the rER 3. Protein
is stored in the cisternae of the rER 4. Vesicles bud off cisternae
and carry protein to the golgi apparatus
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2.4.7 Important Steps for Vesicles 5. Protein is processed in
golgi apparatus 6. Protein is released in more vesicles and moved
to the plasma membrane 7. Vesicle fuses with membrane 8. Protein is
released
Slide 47
2.4.8 Phospholipids in the plasma membrane are able to move
within the bilayer, which results in its fluidity. This fluidity
allows proteins embedded in the cell surface to float around and
between plasma membranes Lateral movement (~10 7 times per second)
Flip-flop (~ once per month)
Slide 48
2.4.8 Membrane Fluidity
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2.4.8 Bulk transport across the plasma membrane occurs by
exocytosis and endocytosis. In exocytosis, transport vesicles
migrate to the plasma membrane, fuse with it, and release their
contents In endocytosis, the cell takes in macromolecules by
forming new vesicles from the plasma membrane
Slide 50
2.4.8 Bulk transport across the plasma membrane occurs by
exocytosis and endocytosis. In exocytosis, transport vesicles
migrate to the plasma membrane, fuse with it, and release their
contents In endocytosis, the cell takes in macromolecules by
forming new vesicles from the plasma membrane
Slide 51
2.4.8
Slide 52
Example in cells: WHITE BLOOD CELL ENGULFING BACTERIA using
Phagocytosis SEE PHAGOCYTOSIS MOVIE
http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x28.jpg
Slide 53
EXOCYTOSIS Active transport (requires ATP) Uses vesicles
Releases substances to outside INSULIN being released by pancreas
cells using exocytosis
2.4.8 http://programs.northlandcollege.edu/biology/Bi
ology1111/animations/active1.swf
http://programs.northlandcollege.edu/biology/bio
logy1111/animations/passive1.swf Passive Transport Active
Transport