Biochemistry

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Biochemistry

• Lipids

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Lipids

• 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

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Lipids

• Classification
• Saponifiablecan be hydrolyzed by NaOH to make
  soap
• Non-saponifiablecannot 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

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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.

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Simple LipidsFatty 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

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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.

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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.

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Waxes

• 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.

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Homework 16-a

• p. 409 CYU all
• p. 422 ff 1, 2, 3, 5, 7, 8, 12, 14

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Reactions of Lipids

• Iodine numberiodine 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 saturation
• Hydrogenationhydrogen can be added to
  unsaturated fats to make them saturated and
  therefore more solid. This is done to make
  margarine and vegetable shortening.
• Rancidityforming 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.

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Examples

• Iodine number
• Hydrolysis
• Oxidation

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Saponification

• 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.

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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

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Hard Water

• Water containing acid, Ca2, Mg2, Fe2, or Fe3
  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.

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Homework 16b

• p. 414 CYU all
• p 423 ff 15, 17, 20, 22, 23, 24

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Compound Lipids

• Phospholipidslipids which contain a phosphate
  group instead of on 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

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Sphingolipids

• 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

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Glycolipids

• 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

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Non-Saponifiable Lipids

• Steroidsany molecule with the four ring
  structure
• Sterolssteroid 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.

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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.

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Homework 16c

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