The Cell Membrane and Transport

A fluid mosaic with a double layer of phospholipids with embedded proteins.

Jobs: Regulates exchangeCreates a barrierCommunicationIdentification

Phospholipids have both hydrophilic and hydrophobic regions

The proteins form a mosaic pattern on the membrane. 

Cholesterol - stiffens membrane by connecting phospholipidsGlycolipids - signal moleculesGlycoproteins - have an chain of sugar (antibodies)

Proteins embedded in the bilayer

1. Channel Proteins - form small openings for molecules to diffuse through2. Carrier Proteins- binding site on protein surface "grabs" certain molecules and pulls them into the cell Gated Channels - similar to carrier proteins, not always "open"

3. Receptor Proteins - molecular triggers that set off cell responses (such as release of hormones or opening of channel proteins), binding site4. Recognition Proteins - ID tags, to identify cells to the body's immune system5. Enzymatic Proteins – carry out specific reactions

Aquaporin

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)

OSMOSISOsmosis - diffusion of water.                                              

Osmosis affects the turgidity of cells, different solution can affect the cells internal water amounts

Salt Sucks!Simple rule of osmosis 

Isotonic - no net movementHypotonic - water moves into the cell, cell could burstHypertonic - 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?