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

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

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

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

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

Water is Sticky!

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

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

Hydrophobic or Hydrophilic? H 2 SO 4

The Cell Membrane water hydrophobic membrane outside cytoplasm

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

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

 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 

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

Triglycerides (Triacylgylcerides, “Fats”)

Phospholipids

 building blocks of membranes Phospholipids

 building blocks of membranes Phospholipids

 building blocks of membranes Phospholipids

 building blocks of membranes Phospholipids

 building blocks of membranes Phospholipids

 building blocks of membranes Phospholipids

 Phospholipids diffuse in two dimensions Membranes are fluid

 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

 Lipids  Ring system: 3x6 + 5 Steroids

 Hydrophilic or hydrophobic? Cholesterol

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