1. Cell Size and Diffusion
Diffusion relies upon surface area
Larger cells have less surface area per volume

2. Other examples of increasing surface area
Roots have microscopic hairs
Intestines have villi projections
Lungs have alveoli

3. Protein Shape

4. Function Depends on Shape
For all proteins, not just enzymes
Change in shape= change in function (or activation/deactivation of function)

5. Example: Protein Receptors

6. Example: Protein Channels

7. Example: Protein Pumps

8. “Activating Proteins”
Phosphorylating or adding a phosphate group is a common mechanism

9. Example: Accessing DNA

10. Special Example: Hemoglobin

11. Cooperativity in Hemoglobin
The binding of the first oxygen molecule changes the shape of hemoglobin
Makes it easier to bind 3 more

12. Why Should We Care?
Hemoglobin only holds oxygen when there is a moderate amount of oxygen present
Allows hemoglobin to pick up lots of oxygen in lungs (lots of O2) and drop most of it off at organs (low O2)

13. Oxygen Disassociation Curve

14. Myoglobin – No Cooperativity

15. Myoglobin vs. Hemoglobin

16. Summary Hemoglobin picks up O2 in lungs, releases it near tissues
Myoglobin holds O2 until there is almost none left

17. Another Factor Affecting Hemoglobin

18. Buffers maintain stable pH
If solution is basic, release acid H2CO3  H+ + HCO3- If solution is acidic, absorb acid H+ + HCO3-  H2CO3 Keeps pH relatively stable to prevent denaturation of proteins