Facilitated Diffusion

Review What do you know about membrane’s permeability? Small and uncharged particles can get easily through Large or charged particles cannot Toxicity does not matter Concentration Gradient: substances move from high to low concentration Diffusion

Lead Lead is charged A lot of lead can get into our cells Lead accumulates in certain tissues more than others Does the squeeze model (simple diffusion) apply to the case of Lead poisoning? Cannot squeeze because of charge

Therefore… If lead is charged and cannot simply diffuse through the membrane… Squeeze Channel Active

Is it possible lead can get in through a protein channel? Many membranes have protein channels that allow molecules to cross the membrane. Still diffusion: high  low concentration

Facilitated Diffusion Uses transport proteins to move molecules from high concentration to low concentration Example: glucose or amino acids moving from blood into cells Does not require energy

Passive Transport Animation Facilitated Diffusion

Passive Transport: The Bouncer The Doorman Protein channel Carrier Protein Carrier-binding of substrate causes shape change in transport protein The Bouncer The Doorman

Aquaporins Channel protein that allows the rapid of water into and out of the cell Simple diffusion straight through the membrane also occurs with water!

Now about that lead… How could we test to see that lead gets into the cell through a protein channel? Each time a student proposes an idea ask: ok so what will that show us about how lead gets into the cell? What does your test show? Possibilities: blocking it, getting rid of the protein Guide students towards removing proteins, or making proteins not function.

Protease There is a way to get rid of proteins. We can use a substance called protease to do this. Protease- a substance that clips off parts of protein to make smaller dysfunctional proteins Deactivates the protein = they cannot work as channels

Lead Transport Experiment Read Facilitated Diffusion and answer questions After you answer question 2, raise your hand for the last data sheet. Finish questions 3,4,5 and stop.

In Conclusion If lead is charged and cannot simply diffuse through the membrane If lead requires energy to cross the membrane Squeeze Channel Active

Active Transport Requires ATP (energy!) Do the molecules travel up or down the concentration gradient? UP/against, from low to high concentration

Revise your original model How do lead particles get into our cells? Revise your model using REASONS and JUSTIFICATION What sorts of reasons or evidence did you use to justify your revisions? How did you know what to change in the model? Can you explain why your new model is better than your original?

For Next Class Why do you think lead is actively transported into cells if it is poisonous?

3 Graphs…which do you like best? #1 #2 Let’s look at the first graph, which groups like it? Why did you like it? Do any other groups disagree with their choice? Which graph did you like and why? What is really important to have in a graph? Do all graphs have this? Do any of the graphs have information or parts that are not necessary? #3