Lipids Lipids are composed of C, H, O – long hydrocarbon chains (H-C) “Family groups” – fats – phospholipids – steroids Do not form polymers – big molecules made of smaller subunits – not a continuing chain
Fats Structure: – glycerol (3C alcohol) + fatty acid fatty acid = long HC “tail” with carboxyl (COOH) group “head” 12-20 carbons- Always an even number. These extensive chains make fats very nonpolar. dehydration synthesis H2OH2O enzyme
Fats (Tricylglycerols) Fats constructed of two kinds of smaller molecules – Glycerol - Three carbons covalently bound to one another, each with a single hydroxyl group.
Function of Fats Energy storage. 1 gram of fat stores more than 2x the energy of 1 gram of carbohydrate. Insulation. Fat is an exceptional thermal and electrical insulator.
Formation of Fats Fats form as a result of a dehydration reaction between glycerol and a fatty acid. This kind of linkage is called an ester linkage. Ester linkage = between OH & COOH Fatty acid (palmitic acid) (a) Dehydration reaction in the synthesis of a fat Glycerol
Fats store energy Long HC chain – polar or non-polar? – hydrophilic or hydrophobic? Function: – energy storage concentrated – all H-C! 2x carbohydrates – cushion organs – insulates body think whale blubber! Why do humans like fatty foods?
Saturated v. Unsaturated Fats Saturated fats are composed of fatty acid chains that contain no double bonds. – Saturated with hydrogens. Unsaturated fats are composed of fatty acid chains with double bonds. – They are not saturated. Naturally occurring fatty acid chains are all cis-fats.
Saturated fats All C bonded to H No C=C double bonds – long, straight chain – most animal fats – solid at room temp. contributes to cardiovascular disease (atherosclerosis) = plaque deposits
Unsaturated fats C=C double bonds in the fatty acids – plant & fish fats – vegetable oils – liquid at room temperature the kinks made by double bonded C prevent the molecules from packing tightly together mono-unsaturated? poly-unsaturated?
Fig. 5-12b (b) Unsaturated fat Structural formula of an unsaturated fat molecule Oleic acid, an unsaturated fatty acid cis double bond causes bending
Fig. 5-12a (a) Saturated fat Structural formula of a saturated fat molecule Stearic acid, a saturated fatty acid
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 – forms barrier between cell & external environment
Phospholipids Structure: – glycerol + 2 fatty acids + PO 4 PO 4 = negatively charged It’s just like a penguin… A head at one end & a tail at the other!
Phospholipids Hydrophobic or hydrophilic? – fatty acid tails = – PO 4 head = – split “personality” interaction with H 2 O is complex & very important! “repelled by water” “attracted to water” hydrophobic hydrophillic
Fig. 5-13 (b) Space-filling model (a)(c) Structural formula Phospholipid symbol Fatty acids Hydrophilic head Hydrophobic tails Choline Phosphate Glycerol Hydrophobic tails Hydrophilic head
Phospholipids in water Hydrophilic heads “attracted” to H 2 O Hydrophobic tails “hide” from H 2 O – can self-assemble into “bubbles” bubble = “micelle” can also form a phospholipid bilayer bilayer water
Phospholipids Similar to fats in structure. Three components – Glycerol – 2 Fatty acids – Phosphate group Phosphate group replaces the 3 rd fatty acid in tricylglycerol
Phospholipid Properties Phospholipids are amphipathic. In an aqueous environment the hydrophobic tails of phospholipids are pushed together while the heads interact with water and each other. Because of this, phospholipids spontaneously take on a characteristic bilayer arrangement.
Functional Importance of Phospholipids Phospholipid bilayer is the primary component of biological membranes http://academic.brooklyn.cuny.edu/biology/bio4fv/page/lipos.gif
Importance of Phospholipids Water and ions cannot freely diffuse through the bilayer. Phospholipids keep the inside of the cell inside the cell and the outside of the cell outside the cell. There are proteins embedded in the phospholipid bilayer that allow select polar molecules and ions through the bilayer.
Why is this important? Phospholipids create a barrier in water – define outside vs. inside – they make cell membranes!
Steroids Steroids are another class of lipids. They are hydrophobic and always have the same root structure. Functional groups attached to the steroid structure greatly influence the biological action of the steroid.
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
Important Steroids http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch26 /ch26-5-1.html
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 helps keep cell membranes fluid & flexible Important component of cell membrane
From Cholesterol Sex Hormones What a big difference a few atoms can make!
How are Phospholipids different than fats? The phosphate is charged. This makes that part of the molecule _________________________ The fatty acid chains are _________________________
Function of Steroids Component of cell membranes (cholesterol). Hormones
Questions to Consider Steroids including cholesterol are do not usually travel alone in the bloodstream. Why not? Suppose a phopholipid membrane surrounded an oil droplet. It frequently does in plant seeds. What form might the membrane take on in these cases?