1.  Semi-permeable barrier  Water on both sides The Cell Membrane water membrane outside cytoplasm

2.  Semi-permeable barrier  Water on both sides The Cell Membrane water membrane outside cytoplasm stuff

3.  Semi-permeable barrier  Water on both sides The Cell Membrane water hydrophobic membrane outside cytoplasm stuff

4.  Water is a polar molecule  Electronegative oxygen pulls e – toward it  Unequal sharing = partial charge Water HH O : : ++ ++ ––

5.  Polar molecules attract each other  Hydrogen bonds (weak) Water

7. Water is Sticky!

8.  Interact with polar water  Form hydrogen bonds  Dissolve  Ions and polar molecules Hydrophilic molecules Na + Cl – Na + protein + + + – – –

9.  Share electrons equally  Uncharged  Can’t interact with water Hydrophobic molecules

10. Hydrophobic or Hydrophilic? H 2 SO 4

11. The Cell Membrane water hydrophobic membrane outside cytoplasm

12.  Fatty acids  Triglycerides (“fats”)  Phospholipids  Steroids Lipids: Hydrophobic molecules

14.  Melting point depends on density and stability of packing Fatty Acids stearic acid (C18): m.p. 69°C solid at room temp.

15.  Melting point depends on density and stability of packing Fatty Acids stearic acid (C18): m.p. 69°C solid at room temp. palmitic acid (C16): m.p. 63°C solid at room temp.  higher lower  myristic acid (C14): m.p. 54°C solid at room temp.  higher lower  oleic acid (C18:1): m.p. 16°C liquid at room temp.  higher lower  linoleic acid (C18:2): m.p. 5°C liquid in refrigerator  higher lower   -linoleic acid (C18:3): m.p. -11°C liquid below freezing  higher lower 

16.  Melting point depends on density and stability of packing Fatty Acids

17. Triglycerides (Triacylgylcerides, “Fats”)

18. Phospholipids

19.  building blocks of membranes Phospholipids

20.  building blocks of membranes Phospholipids

21.  building blocks of membranes Phospholipids

22.  building blocks of membranes Phospholipids

23.  building blocks of membranes Phospholipids

24.  building blocks of membranes Phospholipids

25.  Phospholipids diffuse in two dimensions Membranes are fluid

26.  How could we make the membrane more fluid?  How could we make the membrane less fluid?  How would changing fluidity affect permeability? Membranes are fluid

27.  Lipids  Ring system: 3x6 + 5 Steroids

28.  Hydrophilic or hydrophobic? Cholesterol

29.  Fills gaps in animal membranes  Regulates fluidity  More fluid or less fluid with cholesterol? Cholesterol