Membranes & Lipids

1. Membranes & Lipids

2. Phosphate head group Fatty acid tails Membranes • ALL cells are surrounded by at least one membrane • Membranes are composed of phospholipids

3. Phospholipid Bilayer Membrane Structure • Hydrophobic tails interact with each other • Hydrophilic head groups interact with water

4. Molecules with charges (hydrophilic) will be able to interact with water sugar in your coffee Molecules that are uncharged (hydrophobic) will NOT be able to interact with water oil and vinegar in your salad dressing Interactions with Water

5. Why do only charged HYDROPHILIC molecules interact with water? The 2 hydrogen atoms share their electrons with oxygen (covalent bond) BUT the electrons from the hydrogens spend more time around the oxygen atom (polar covalent bond)

7. Summary • Oxygen tries to suck electrons away from other atoms (highly electronegative) • This creates polar covalent bonds between the oxygen and hydrogen atoms in the same water molecule • Polar molecule = parts of the same molecule have opposite charges • Hydrogen bonds form between water molecules because of the attraction between these charges

8. Polar covalent bonds result from unequal sharing of electrons (O-H) Nonpolar covalent bonds result from equal sharing (C-H) Strong bonds that are difficult to break H - O - H Interactions between polar molecules Partial+ charge on one molecule Attracted to partial- charge on another molecule Opposites attract Weak bonds like Velcro H2O ------ H2O Covalent VS. Hydrogen bonds

9. O H H H H H H H H | | | | | | | | C – C – C – C – C – C – C – C – C – H | | | | | | | | OH H H H H H H H H H2O Phospholipid Structure Glycerol backbone Fatty Acid H | H – C – OH | H – C – OH | H – C – OH | H Hydroxyl Group - because of the oxygen, there is polarity Condensation synthesis = the molecules join together with the removal of water. Carboxyl group- makes the hydrocarbon polar so it can interact with other polar molecules

10. Phospholipid- has 2 fatty acids and 1 phosphate group attached to the glycerol backbone

11. Saturated fatty acids are saturated with hydrogens Results in a “stiff” phospholipid Unsaturated fatty acids have double bonds between the carbons Results in a more fluid phospholipid O H H H H | | | | C – C – C – C – C H | | | | OH H H H C – C – H | | H H O H H H H H H H H | | | | | | | | C – C – C – C – C – C – C – C – C – H | | | | | | | | OH H H H H H H H H Saturated vs. Unsaturated Fatty Acids

12. Proportions can change seasonally • Usually have the consistency of salad oil

13. Saturation Affects Membrane Fluidity • Hot springs bacteria - have more saturated fatty acids in their membranes (membranes are more stable at high temperatures) • Arctic fish - have more unsaturated fatty acids (membranes are more fluid at low temps.)

14. Fats & Oils • Saturated fats are produced by animals and are solid at room temp. • Unsaturated fats (oils) are produced by plants and are liquid at room temp. • Structurally similar to phospholipids • Instead of a phosphate head group, have a third fatty acid

16. So how do you make a solid margarine from canola oil? • Plant oils are unsaturated (lots of double bonds & very kinky) • Hydrogenation gets rid of the double bonds and makes the oil act like a fat

17. Can lead to the formation of excess CHOLESTEROL Steroid that helps stabilize membranes of animal cells So why are saturated fats bad for me?

18. Is there such a thing as a “good” fat? • Polyunsaturated fats (>1 double bond) contain essential fatty acids (omega-3) • First double bond located 3 carbons from the methyl end of the fatty acid (-CH3) • Methyl end = omega end • May protect against heart disease • Oily fish like salmon and tuna (not canned), flax & walnuts

19. My Favourite Fat • Has two saturated stearic acids and one unsaturated oleic acid • Solid at room temperature but melts quickly in your fingers

20. H O | || H – C – O – C – stearic acid O || H – C – O – C – oleic acid O || H – C – O – C – stearic acid | H Cocoa butter!!!!