Transcript Cell Membranes: Chapt. 6

Cell Membranes
The Cell
Membrane
Cell Membrane:
At Very High
Magnification
& in color
Phospholipid Molecule Model
phosphate (hydrophilic/polar)
glycerol
fatty acids (hydrophobic/nonpolar)
Membrane Structure
Hydro
Philic/philia
Phobic/phobia
Polar=soluble in water
Cell Membrane
Every cell is encircled by a membrane and most cells contain an
extensive intracellular membrane system. Membranes fence off the
cell's interior from its surroundings. Membranes let in water, certain
ions and substrates and they excrete waste substances. They act to
protect the cell.
Without a membrane the cell contents would diffuse into the
surroundings, information containing molecules would be lost and
many metabolic pathways would cease to work:
The cell would die!
Cell Membranes:
• Surround all cells
• Fluid-like composition…like soap bubbles
• Composed of:
–
–
–
–
Lipids in a bilayer
Proteins embedded in lipid layer (called transmembrane proteins)
And, Proteins floating within the lipid sea (called integral proteins)
And Proteins associated outside the lipid bilayer (called peripheral
proteins).
Membrane Lipids
• Composed largely of phospholipids
• Phospholipids composed of….glycerol and two
fatty acids + PO4 (phosphate) group
• Phospholipids are polar molecules…
P-Lipids are
represented
like this
Membrane Lipids
form a Bilayer
Outside layer
Inside Layer
Membrane Proteins
• Integral: embedded within bilayer
• Peripheral: reside outside hydrophobic region of lipids
Membrane Models
Fluid Mosaic Model - lipids arranged in bilayer with
proteins embedded or associated with the lipids.
What color are the lipids?
What color are the integral proteins?
What color are the peripheral proteins?
Fluid Mosaic Model of the Cell Membrane
Evidence for the Fluid Mosaic Model
(Cell Fusion)
Frey and Edidin
Membrane Functions
• allows for different conditions between inside and outside of cell
• subdivides cell into compartments with different internal conditions
• allows release of substances from cell via vesicle fusion with outer
membrane:
Membrane Permeability
• Biological membranes are physical
barriers..but which allow small uncharged
molecules to pass…
• And, lipid soluble molecules pass through
• Big molecules and charged ones do NOT
pass through
• Semi-permeable / selectively permeable
Solution = solute + solvent
Solute-- the thing being dissolved
Solvent--does the dissolving
kool-aid
chocolate milk
Terms that refer to solute:
Hyper
Hypo
Iso
How to get other molecules
across membranes??
There are two ways to move through the membrane:
passive transport and active transport
•Active transport requires energy (that the cell has
obtained from food to move the molecules through the
cell membrane)
•Passive transport does not require energy
Membrane Transport Mechanisms
I. Passive Transport
• Diffusion- simple movement from regions of high
concentration to low concentration
• Osmosis- diffusion of water across a semipermeable membrane
• Facilitated diffusion- protein transporters which
assist in diffusion
Membrane Transport Mechanisms
II. Active Transport
• Active transport- proteins which transport against
concentration gradient.
• Requires energy input (uses ATP)
- Endocytosis
- Exocytosis
- Receptor mediated endocytosis
1.What is the
solute?
2. What diffuses?
3.Why?
4.Is this diffusion
or osmosis?
5.Which side is
hypertonic?
6.Which side is
hypotonic?
7.Why doesn’t the
sugar diffuse?
Osmosis
Movement of water across
a semi-permeable
barrier.
Example: Salt in water,
cell membrane is barrier.
Salt will NOT move
across membrane, water
will.
Osmosis in Hypertonic medium
cell
Hypertonic solutions- shrink cells
Plasmolysis in Plant Cells
Crenation in Animal Cells
What happens when you eat salty chips?
Osmosis in Hypotonic medium
Hypotonic solutions- swell cells
“Hypos make hippos”
Cytolysis in Animal Cells
Turgor Pressure in Plant Cells
http://www.kscience.co.uk/animations/turgor.htm
For more animations view:
http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
For Osmosis in Action
View frozen frogs at:
http://www.pbs.org/wgbh/nova/sciencenow/
3209/05.html
How did the frog use the principles of
osmosis and diffusion to survive the
winter? Make sure you use the following
terms appropriately in your description:
hypertonic, hypotonic, solute, solvent,
diffusion, osmosis, cytolysis, crenation,
isotonic and semi-permeable membrane.
Osmosis & Food Preservation
• Food can be preserved by causing
any microorganism that comes in
contact with it to become
plasmolysed and, therefore, shrivel
and die. To do this food is placed in a
high salt or sugar medium. The salt
or sugar concentration is higher than
the cytoplasm of bacteria or fungi.
Bacteria or fungi, that contaminate
the food, will lose water by osmosis
and their metabolism will decline.
Many will die but some bacteria may
survive by forming dormant resistant
endospores. Meat and fish are often
preserved in salt. Fruit is commonly
preserved in sugar as in jam or syrup.
Endocytosis
• Transports
macromolecules
and large particles
into the cell.
• Part of the
membrane
engulfs the
particle and folds
inward to “bud
off.”
Phagocytosis
• Pseudo pods
• Phago cytes
• Macro phages (phage)_
Putting Out the Garbage
• Vesicles (lysosomes, other secretory
vesicles) can fuse with the membrane and
open up the the outside…
Exocytosis
(Cellular Secretion)
Types of Protein Transporters
A. Facilitated Diffusion
Assist in diffusion process.
Solutes go from High conc
to Low conc.
Examples: Glucose transporters
Carrier Proteins
Protein Channels
Types of Protein Transporters:
Active Transport
• carrier proteins
• go against the concentration gradients Low
to High
• require Energy to function (ATP, PEP, light
energy, electron transport)
Membrane Transport:
Active transport
• Movement from region of low free
energy(low concentration) to regions of
high free energy (high conc.)
• Requires energy input
Sodium-Potassium Pump
Resources
• http://users.rcn.com/jkimball.ma.ultranet/BiologyPages
/C/CellMembranes.html
• www.biologie.uni-hamburg.de/b-online/e22/22.htm
• More Animations:
http://www.kscience.co.uk/animations/anim_1.htm
• http://fig.cox.miami.edu/~cmallery/150/memb/membran
es.htm
• Pictures: http://biologycorner.com/resources/
• 1st Semester Final Review