1. Membrane Structure and Function

2. Model 1 – Simple Diffusion
Two types of molecules
Triangles – 14 on left
Cirlces – 12 on left, 13 on right
Triangle is larger
The molecules will move in all directions (that’s diffusion)
The dots can fit through the gaps because they are small and they are equally distributed on both sides
No change from this point since the triangles are too big to fit through the membrane and the dots are already spread out evenly

3. Model 2 – The Selectively Permeable Cell Membrane
Phospholipids and Proteins
Four - 2 types of surface proteins and 2 membrane-spanning proteins
Surface protein is either on the inside or outside whereas the membrane-spanning proteins reach across the whole membrane
Glycoprotein
Glycolipid
Small polar and nonpolar molecules
Between phospholipids
More small molecules are outside compared to the inside so we say … the concentration is higher outside
No, molecules are moving in as shown by the arrows because it started with more outside.

4. Concentration Gradients (high to low = downhill)
Dots in Model 1, small molecules in Model 2
A) Diffusion is the net movement of molecules from an area of HIGH to LOW concentration. B) The molecules continue to move along the concentration gradient until reaching equilibrium. C) Molecules continue to move randomly.

5. Model 3 – Facilitated Diffusion
Membrane spanning protein
Gated channel
Hormones
Hormone attaches and works like a “key” to open the gate.

6. The protein channel acts like a gate with the hormone as the key
Facilitated means the molecules get “help” to move across the membrane, but they still move from high to low concentration
The nonpolar phospholipid tails provide a barrier that prevents the Na+ and K+ from crossing the membrane unless through a channel.

7. Model 4 – Active Transport
Membrane spanning proteins
Diamond
ATP and ion binding sites
Low to High concentration
No, the substance is being moved up a concentration gradient
Energy (ATP) is used to change the shape of the protein channel
ATP changes to ADP
Active transport moves molecules up concentration gradients whereas passive transport moves molecules down concentration gradients

8. Complete the Summary Chart - #33

9. Active Transport Definition - #34
Movement of a substance up it’s concentration gradient, using energy input (ATP) from the cell and requiring membrane protein channels.

10. Extension Questions Active Transport Diffusion
Facilitated diffusion relies on proteins … the # of protein channels will set a limit as to how fast diffusion can happen
Active transport does not rely on concentration gradient. It relies on a supply of energy.