CAPE BIOLOGY UNIT 1 SEPTEMBER 24, 2010 MRS. HAUGHTON

 A mixed group of hydrophobic compounds.  Composed of the C, H and O.  Lipids are fats and oils (fats are solid at room temperature; oils are liquid).

 Triglycerides are commonly called fats or oils.  They are made of glycerol and fatty acids.

 Triglycerides are insoluble in water.  They are used for storage, insulation and protection in fatty tissue (or adipose tissue) found under the skin or surrounding organs.  They yield more energy per unit mass than other compounds so are good for energy storage.  However, Carbohydrates can be mobilised more quickly, and glycogen is stored in muscles and liver for immediate energy requirements.

 Triglycerides containing saturated fatty acids have a high melting point and tend to be found in warm-blooded animals. At room temperature they are solids (fats), e.g. butter, lard.  Triglycerides containing unsaturated fatty acids have a low melting point and tend to be found in cold-blooded animals and plants. At room temperature they are liquids (oils), e.g. fish oil, vegetable oils.

 Glycerol is a small, 3-carbon molecule with three hydroxyl groups.

 Fatty acids are long molecules with a polar, hydrophilic end and a non-polar, hydrophobic "tail".  The hydrocarbon chain can be from 14 to 22 CH 2 units long.  The hydrocarbon chain is sometimes called an R group, so the formula of a fatty acid can be written as R-COOH.

 Common fatty acids n = 4 butyric acid (butanoic acid) n = 6 caproic acid (hexanoic acid) n = 8 caprylic acid (octanoic acid) n = 10 capric acid (decanoic acid)

Common FA’s n = 12: lauric acid (n-dodecanoic acid; C12:0) n = 14: myristic acid (n-tetradecanoic acid; C14:0) n = 16: palmitic acid (n-hexadecanoic acid; C16:0) n = 18; stearic acid (n-octadecanoic acid; C18:0) n = 20; arachidic (eicosanoic acid; C20:0) n= 22; behenic acid n = 24; lignoceric acid n = 26; cerotic acid

 Fatty acids are amphipathic molecules with the hydrocarbon tail serving as hydrophobic region and the carboxyl group (-COOH) serving as a hydrophilic region.  Amphipathic molecules contain both polar (water-soluble) and non-polar regions in its structure.

 Fatty acids differ from one another not only by the number of carbons in their chain, but by the number of double-bonds between the carbon atoms.  Bonds between carbons may be single (C- C) or double (C=C).

 Fatty acids with only single-bonds are called saturated because they are "saturated" with as many hydrogen atoms as they can carry.

 The presence of double bonds implies that the carbon chain of a fatty acid is not saturated with hydrogen atoms.  That is, less than the maximum number of hydrogen atoms possible are bound to the carbon chain.

 Fatty acids with only one double-bond are called mono- unsaturated.  And fatty acids with more than one double-bond are called poly- unsaturated.

 Double bonds may be either of the cis- type or the trans-type.  Only the cis-type are found in biological systems.  The cis-type double bond, unlike the trans-type double bond, bends or kinks the hydrocarbon chain of the fatty acid.

 Triglycerides consist of three fatty acids bound to a molecule of glycerol through three separate condensation (dehydration) synthesis steps.  A molecule of glycerol is covalently attached (via an ester linkage) to a single saturated fatty acid.

 Phospholipids have a similar structure to triglycerides, but with a phosphate group in place of one fatty acid chain.  There may also be other groups attached to the phosphate.

 Phospholipids have a polar hydrophilic "head" (the negatively-charged phosphate group)  And two non-polar hydrophobic "tails" (the fatty acid chains).  This mixture of properties is fundamental to biology, for phospholipids are the main components of cell membranes.

 When mixed with water, phospholipids form droplet spheres with the hydrophilic heads facing the water and the hydrophobic tails facing each other.  This is called a micelle.

 Alternatively, they may form a double- layered phospholipid bilayer.  This traps a compartment of water in the middle separated from the external water by the hydrophobic sphere.  This naturally-occurring structure is called a liposome, and is similar to a membrane surrounding a cell.

 LYPOSOME

 The membrane surrounding cells is a bi-layer similar in behaviour to the liposome.  The hydrophilic phosphate heads point out while the hydrophilic fatty acid tails point in.

 Waxes are esters of an alcohol other than glycerol.  Long-chain, non-polar lipids forming a protective coating (cutin in the cuticle) on plant leaves and fruits but also in animals.  Water-resistant materials.  Have long carbon chains (from 12 up to about 38 carbon atoms) and solid in a large range of temperature (fusion point between 60 and 100°C).

 A steroid is a type of organic compound that contains a specific arrangement of four rings that are joined to each other.  Examples of steroids include cholesterol, the hormones estradiol an d testosterone.