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Biochemistry Powered By Docstoc

Lipids are biochemicals which are not water
  soluble since they more closely resemble
  hydrocarbons. Included in this class are
  fats, oils, some vitamins and hormones, and
  an important part of cell membranes and
  nerve linings. They serve as energy storage,
  structural molecules, and starter materials
  for other important biochemicals
  Saponifiable—can be hydrolyzed by NaOH
  to make soap
  Non-saponifiable—cannot be hydrolyzed,
  includes sterols such as cholesterol
Saponifiable lipids are further subdivided:
  Simple- made of fatty acids plus alcohol
  Compound- either phospho- or glyco-
  lipids, which contain phosphate or sugar
  groups as well as fatty acids
                 Fats & Oils
Simplest lipids, called triacylglycerols or
  simply triglycerides. Main form of fat
  storage in plants, animals, and man. Males
  store 21% fat on average, females 26%.
       Simple Lipids—Fatty Acids
Simple triglycerides contain the same fatty acid in
  all three positions; mixed triglycerides contain
  two or three different fatty acids
Fatty acids are carboxylic acids with from 4 to 20
  carbons in the chain. The chain can be saturated
  (only single bonds) or unsaturated (one or more
  double bonds in the chain), Saturated are
  usually solid at room temperature, unsaturated
  are usually liquid
             Fatty Acids
The difference between fats and oils has
 to do with the number of unsaturated
 fatty acids present. Butter, lard, and
 “Crisco” have mostly saturated fats.
 Vegetable oils have a much higher
 concentration of unsaturated fats.
Essential Fatty Acids
Fatty acids which cannot be made by the body, but are
  important for health and growth are called essential.
Linolenic acid, found mostly in vegetable oils, is an
  important reducer of LDL (low density
  lipoproteins), which help to take cholesterol into the
  blood and cause atherosclerosis (buildup of plaque
  in the blood vessels) a prime cause of heart attacks
Arachidonic acid is important in making eicosanoids,
  molecules which regulate and protect the body from
  invasion by microorganisms.
Waxes are simple lipids which are esters of long chain
 alcohols and fatty acids. Beeswax is a 30 C alcohol
 connected to a 16 C fatty acid

Waxes are completely water resistant and make the coatings
 on leaves, skin, feathers, fur, and fruit. They can be used
 on floors and furniture for the same protecting quality.
          Homework 16-a

p. 409 CYU all
 p. 422 ff 1, 2, 3, 5, 7, 8, 12, 14
Reactions of Lipids
Iodine number—iodine has a great affinity for double bonds in
  fatty acids. The amount which can be absorbed is called the
  iodine number. A reading over 70 indicates a great deal of
  unsaturation, less than 70 is very little or complete
Hydrogenation—hydrogen can be added to unsaturated fats to
  make them saturated and therefore more solid. This is done
  to make margarine and vegetable shortening.
Rancidity—forming bad odor and taste from fats by
  hydrolysis and oxidation. Hydrolysis splits the glyceride
  link, oxidation breaks up the fatty acid at the double bonds,
  making short acids and aldehydes. To stop this, antioxidants
  like BHA, BHT, and vitamin E are added.
Iodine number:


When hydrolysis happens due to a strong base, saponification
 happens, just as in esters before. In this case, three soap
 molecules are made:

These soaps are hard or soft depending on the amount of
  unsaturation in the carbon chains.
Action of Soap
How do soaps work? With a polar head (the
 sodium/carboxyl portion), soap is soluble in water. The
 long nonpolar tail allows the soap to attach to grease
 particles and create a micelle, a “bubble” of soap
 molecules surrounding the grease. The micelles carry
 away the grease and dirt with them in the rinse water
             Hard Water
Water containing acid, Ca+2, Mg+2, Fe+2, or
 Fe+3 will react with the soap to form
 “scum”. To stop this, those ions can be
 removed through softening or by using
 detergents. Detergents have a sulfate head
 rather than a carboxyl, and are not affected
 by the hard water ions or by acid.
         Homework 16b

p. 414 CYU all
 p 423 ff 15, 17, 20, 22, 23, 24
                 Compound Lipids
Phospholipids—lipids which contain a phosphate group
  instead of one of the fatty acids on a glycerol
                                  X can be several
                                  different compounds

Phospholipids are important in forming cell membranes and in
  transporting other lipids in the body. Phosphatidyl choline
  is one which the body uses in the liver, and is used in
  industry to make candy and medicine quaternary ammonium salt
  X= choline
If instead of glycerol, another alcohol with two links,
   sphingosine, is used, sphingolipids are formed. These have
   one phosphate and one fatty acid

                         If X is choline, as above,
                         this would be sphingomyelin,
                         a covering for nerve fibers
Instead of phosphate, sugar goups could be attached
  to either a glycerol or sphingosine to make a
  glycolipid. The usual sugar is galactose, but may
                                 be glucose

Glycolipids are commonly found in nerve coverings
             Non-Saponifiable Lipids
Steroids—any molecule with the four ring structure:

Sterols—steroid alcohols such as cholesterol. Cholesterol is
  formed from acetyl coenzyme A in the liver and makes part
  of cell membranes. Some important chemicals made from
  cholestrerol are bile acids, steroid hormones, and vitamin D.
Too much cholesterol can build up in the arteries as mentioned
  before. LDL brings cholesterol into the blood, where it can
  build up, HDL removes it, so that a good diet would be one
  which encourages HDL and limits LDL.
           Lipids in the Body
The primary site of lipids in the body is in cell
  membranes. Due to the polar-nonpolar nature of
  lipids, the cell membrane is often a bi-layer
  structure, with the non-polar parts inward.
Membranes throughout the body are of different
  percent compositions, depending on what they
  need to do. Since nerves must be kept from too
  much water, nerve coatings are around 70% lipid.
  The nuclear membrane, which must allow fluids to
  pass easily, is only about 40%.
         Homework 16c

p. 420 CYU all
 p. 424 ff 25, 29, 31, 32, 35, 39

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