The Cell Membrane and Transport
A fluid mosaic with a double layer of phospholipids with
embedded proteins.
Jobs:
Regulates exchange
Creates a barrier
Communication
Identification
Phospholipids have both hydrophilic and hydrophobic regions
The proteins form a mosaic pattern on the membrane.
Cholesterol - stiffens membrane by connecting phospholipids
Glycolipids - signal molecules
Glycoproteins - have an chain of sugar (antibodies)
Proteins embedded in the bilayer
1. Peripheral proteins – do not go all the way through the bilayer
2. Integral proteins – pass through the entire bilayer from the outside of the cell
to the inside
a. Each protein is specialized to allow certain molecules to pass through its
interior
3. Receptor Proteins - molecular triggers that set off cell
responses (such as release of hormones or opening of
channel proteins), binding site
4. Recognition Proteins - ID tags, to identify cells to the
body's immune system
5. Enzymatic Proteins – carry out specific reactions
Transport Across Membrane
*Selectively
permeable – only
some things can
cross
What things can
pass?
What cannot pass?
Passive Transport (no energy)
Simple Diffusion - water, oxygen and other molecules move from
areas of high concentration to areas of low concentration, down a
concentration gradient
Facilitated Transport (Diffusion) - diffusion that is assisted by
proteins (channel or carrier proteins)
OSMOSIS
Osmosis - diffusion of water.
Osmosis affects the turgidity of cells, different solution can
affect the cells internal water amounts
Simple rule of osmosis
Salt Sucks!
Isotonic - no net movement
Hypotonic - water moves into the cell, cell could burst
Hypertonic - water moves out of the cell, cell shrinks
salty outside
Contractile Vacuoles are
found in freshwater
microorganisms - they pump
out excess water
Turgor pressure occurs in plants cells as their central
vacuoles fill with water.
Osmosis in U Tubes
Active Transport
- involves moving molecules "uphill" against the concentration
gradient, which requires energy
Endocytosis - taking substances into the cell
(pinocytosis for water, phagocytosis for solids)
Exocytosis - pushing
substances out of the cell, such
as the removal of waste
Sodium-Potassium Pump - pumps out 3
sodiums for every 2 potassium's taken in against
gradient
A huge amount of energy in our bodies is used
to power this pump and prevent sodium from
building up within our cells.
What would happen if you had too much sodium
in your cells?
SODIUM
POTASSIUM
PUMP
See also McGraw Hill Animation
Mini Labs and Demos
1. Place a baggie full of starch in a beaker that has iodine (an
indicator for starch). Observe what happens.
2. Create a wet mount of elodea (anacharis) and observe what
happens to the cells when you add salt water.
3. Observe what happens when food coloring is placed in a
beaker of water. How does the process change if the water is
heated first?
*AP Lab on diffusion and osmosis:
http://www.biologycorner.com/worksheets/diffusion_lab_AP.html
Podcast on the cell membrane by Paul Anderson. (Youtube channel = Bozeman Science)
1. What are the two kinds of transport in a cell?
2. What type of transport brings oxygen into the lungs?
3. Describe the U-Tube experiment.
4. Why does the slug die when you put salt on it?
5. What happens if you inject salt water into blood?
6. How is glucose taken into the cell? Does this require energy?
7. The Sodium Potassium pump moves ___ to the outside and ____ to the
inside, a process that requires ________.
8. Compare endocytosis to exocytosis.
9. What is a phagolysosome?