Lipids AP Biology 2006-2007

Lipids

Lipids Lipids are composed of C, H, O Major Types of Lipids long hydrocarbon chains (H-C) Major Types of Lipids Fats and oils phospholipids Steroids Waxes Made of same elements as carbohydrates but very different structure/ proportions & therefore very different biological properties

Functions of Lipids Energy Storage Cushion body organs Insulation Think blubber Waterproofing Think duck feathers Cell-to-cell communication Think hormones Formation of cell membranes

Basic Structure of Lipids Do not form “polymers” exactly Not big molecules made of smaller subunits not a “choo-choo train” of monomers Mostly long chains of carbon and hydrogen atoms stuck to a “hook”…. Glycerol = the hook

dehydration synthesis Fats and oils Structure: glycerol (3C alcohol) + fatty acid fatty acid = long HC “tail” with carboxyl (COOH) group “head” enzyme Look at structure… What makes them hydrophobic? Note functional group = carboxyl H2O dehydration synthesis

Building Fats Triglyceride 3 fatty acids linked to glycerol ester linkage = between OH & COOH hydroxyl carboxyl Yet Another type of Covalent bond BIG FAT molecule!!

Dehydration synthesis H2O dehydration synthesis enzyme H2O Pulling the water out to free up the bond enzyme H2O enzyme H2O

Why do humans like fatty foods? very evenly – no polarity Fats store energy Long HC chain polar or non-polar? hydrophilic or hydrophobic? Function: energy storage concentrated all C-H Bonds 2x energy of carbohydrates C and H share electrons very evenly – no polarity results. What happens when you add oil to water Why is there a lot of energy stored in fats? • big molecule • lots of bonds of stored energy So why are we attracted to eating fat? Think about our ancestors on the Serengeti Plain & during the Ice Age. Was eating fat an advantage?

Why is Fat the preferred energy storage molecule of animals Why is Fat the preferred energy storage molecule of animals? (as opposed to starch) More C-H Bonds than in carbs…Remember the Glucose molecule:

C O C C C C 5' 4' 1' 3' 2' CH2OH 6' H OH H OH H H OH H OH Where’s the energy? CH2OH 6' C O In the C-H BONDS!! 5' H OH H C C 4' 1' OH H H OH C C 3' 2' H OH

In lipids there are even MORE C-H bonds than in carbs! Thus, more energy packed in a lipid per unit mass TWICE as much as in a carbohydrate! ALL ENERGY!!!

Saturated vs. Unsaturated Fats Remember that covalent bonds can be Single, double, or triple In Fatty acids, generally the covalent bonds between the carbons are SINGLE However, sometimes a DOUBLE bond can exist between carbons This means the carbons involved in the double bond are “holding hands” with each other and NOT “holding hands” wi A DOUBLE bond can cause BENDING in the carbon chain.

Saturated fats This means that all the carbons are SATURATED with hydrogens! This means each carbon is holding as many hydrogens as it possibly can (2 H’s per C) No C=C double bonds This results in long, straight chains These can pack TIGHTLY together solid at room temp. ANIMAL fats, typically Butter, lard Mostly animal fats

Unsaturated fats C=C double bonds in the fatty acids Called UNsaturated because the carbons are NOT holding hands with as many hydrogens as possible C=C double bonds cause the fatty acid to bend liquid at room temperature the kinks made by double bonded C prevent the molecules from packing tightly together plant & fish fats vegetable oils Mostly plant lipids Think about “natural” peanut butter: Lots of unsaturated fats Oil separates out Companies want to make their product easier to use: Stop the oil from separating Keep oil solid at room temp. Hydrogenate it = chemically alter to saturate it Affect nutrition? mono-unsaturated? poly-unsaturated?

Saturated vs. unsaturated

It’s just like a penguin… Phosphate Phospholipids Often drawn Like this Structure: glycerol + 2 fatty acids + PO4 PO4 = Phosphate group PO4 = negatively charged Fatty Acids It’s just like a penguin… A head at one end & a tail at the other!

Phospholipids Hydrophobic or hydrophilic? fatty acid tails = PO4 head = split “personality” hydrophobic NONPOLAR hydrophillic POLAR “attracted to water” Come here, No, go away! interaction with H2O is complex & very important! “repelled by water”

Phospholipids in water Hydrophilic heads “attracted” to H2O Hydrophobic tails “hide” from H2O can self-assemble into “bubbles” bubble = “micelle” can also form a phospholipid bilayer “bubbles” of phospholipids an early evolutionary step for cells? Animation water bilayer water

Phospholipids & cells Phospholipids of cell membrane double layer = bilayer hydrophilic heads on outside in contact with aqueous solution outside of cell and inside of cell hydrophobic tails on inside form core Phospholipid bilayer Note other molecules in membrane…

Why is this important? Phospholipids create a barrier in water define outside vs. inside they make cell membranes! Tell them about soap!

Steroids Structure: 4 fused C rings + ?? different steroids created by attaching different functional groups to rings different structure creates different function examples: cholesterol, sex hormones cholesterol

Cholesterol Important cell component animal cell membranes precursor of all other steroids including vertebrate sex hormones high levels in blood may contribute to cardiovascular disease

Cholesterol Important component of cell membrane helps keep cell membranes fluid yet firm

From Cholesterol  Sex Hormones What a big difference a few atoms can make! Same C skeleton, different functional groups

Any Questions? 2006-2007