Lipids

1
Lipids

• Module 14

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Lipids

• Lipids are nonpolar compounds
• They are essential for living
• Common lipids include fats, oils, and steroids
• Lipids are a class of biomolecules whose only
  common feature is that they are not soluble in
  water
• The important functions that lipids perform are
• As structural components of membranes
• Energy storage and transport
• As a protective coating
• Metabolic regulation

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Fatty Acids

• Fatty acids are long-chain monocarboxylic (mono
  1) acids that are the major components of fats
  and oils
• Characteristics
• Insoluble in water
• Contain an even number of carbons (usually 12-18)
  arranged in a straight chain
• Can contain all single bonds (saturated) or
  contain some double bonds (unsaturated)
• If more than one double bond is present, the
  fatty acid is called a polyunsaturated fatty acid
• Our bodies can MAKE all required fatty acids from
  the foods we eat except for linoleic acid and
  linolenic acid (two essential polyunsaturated
  fatty acids), which must be IN the food we eat
  (fish, leafy vegetables, vegetable oil, etc.)

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Classification of Lipids

• Lipids are divided into two categories
• Saponifiable lipids esters of fatty acids that
  can undergo saponification
• Saponifiable lipids includes
• Waxes
• Triglycerides
• Phosphoglycerides
• Sphingolipids
• Glycolipids
• Nonsaponifiable lipids lipids that do not have
  fatty acids or ester linkages
• Nonsaponifiable lipids includes
• Steroids
• Terpenes

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Saponifiable Lipids Waxes

• Waxes are esters of fatty acids and long-chain
  alcohols
• They act as protective coatings for hair, skin,
  and feathers, and to protect plants from
  dehydration and insects
• Common waxes include
• Beeswax (shown above), which is the support for
  the honeycomb and is used in pharmaceutical
  produces and expensive candles
• Lanonin, which is obtained from wool and is used
  in lotions and cosmetics
• Carnauba wax, which is obtained from the carnauba
  palm and is used in car and floor waxes
• Spermacetti, which is the oil of the sperm whale
  and is used to make candles

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Saponifiable Lipids Triglycerides 1

• Triglycerides, which are also known as
  triglycerols, are esters of glycerol and three
  fatty acids
• If one fatty acid is present, it is a
  monoglyceride
• If two fatty acids are present, it is a
  diglyceride
• If three fatty acids are present, it is a
  triglyceride

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Saponifiable Lipids Triglycerides 2

• Above is an example of how a triglyceride is made
  (glycerol three fatty acids ? triglyceride)
• Most fats and oils are mixed triglycerides, i.e.
  triglycerides that contain three different fatty
  acids
• Fats are solid at room temperature and are
  obtained usually from animal sources (lard,
  butter, etc.)
• Oils are liquids at room temperature and are
  obtained usually from plant sources (corn oil,
  canola oil, olive oil, etc.)
• Animal at contains more saturated fatty acids
  than vegetable oil

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Hydrolysis of Triglycerides

• Hydrolysis of triglycerides occurs in the
  presence of strong acids or by lipases (an
  enzyme)
• The product of the reaction is glycerol and three
  fatty acids

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An Example of Hydrolysis of Triglycerides

• Problem What is the product of the above
  reaction?
• Steps to the hydrolysis of triglyceride
• Break the bond between the oxygen (O) and the
  carbonyl (CO) group
• Add a hydrogen (from the water) to the oxygen and
  add a OH (from the water) to the carbon of the
  carbonyl group
• See above for the products

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Saponification of Triglycerides

• Saponification of triglycerides occurs in the
  presence of a strong base such as sodium
  hydroxide (NaOH) or potassium hydroxide (KOH)
• The product of the reaction is glycerol and soap
• Sodium salts, soap made when NaOH is used, are
  usually solids and are formed into bars
• Potassium salts, soap made when KOH is used, are
  called soft soaps and are liquids at room
  temperature

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An Example of Saponification of Triglycerides

• Problem What is the product of the above
  reaction?
• Steps to the saponification of a triglyceride
• Break the bond between the oxygen (O) and the
  group attached to the oxygen that doesnt have
  the carbonyl (CO) group i.e. the oxygen will
  end up attached to the group with the carbonyl
  group
• Add a OH (from the base) to the group that
  doesnt have the carbonyl group and add the rest
  of the base to the oxygen that is attached to the
  group with the carbonyl group
• See above for the products

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Cleaning Action of Soap

• The cleaning action of soap is based on the
  simple solubility principle of like dissolves
  like (i.e. - polar solutes dissolve in polar
  solvents, and nonpolar solutes dissolve in
  nonpolar solvents).
• The head of a soap molecule is ionic, polar, and
  hydrophilic (i.e. water-loving), while the
  tail of a soap molecule is covalent, nonpolar,
  and hydrophobic (i.e. water-fearing).
• The tail of the soap molecule dissolves dirt
  since dirt is nonpolar and not soluble in water,
  while the head of the soap molecule provides
  attraction for water molecules. Thus, the soap
  forms an emulsion and carries away the dirt and
  oil. The emulsion can be broken down into
  smaller bodies called micelles with scrubbing.
• Detergents clean in the same way that soap does.

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Hydrogenation of Triglycerides

• Hydrogenation of triglycerides occurs by the
  addition of H2 in the presence of a catalyst (Pt,
  Ni, or Pd)
• Hydrogenation converts the double bonds (i.e.
  unsaturated fatty acids) to single bonds (i.e.
  saturated fatty acids)
• The degree of hydrogenation can be controlled
• Partial hydrogenation produces trans-fatty acids,
  which are not as healthy as cis-fatty acids and
  thus can lead to arteriosclerosis, which is when
  lipid material accumulates in the coronary blood
  vessels and thus narrows the coronary arteries

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An Example of Hydrogenation of Triglycerides

• Problem What is the product of the above
  reaction?
• Hydrogenation adds two hydrogens and thus removes
  the double bond, replacing it with a single bond
• See above for product

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The Food Pyramid

• The U.S. Department of Agriculture (USDA)
  recommends that the Food Pyramid be used as a
  guide for a healthy diet
• A healthy diet includes using fats and oils
  sparingly, as is indicated by the small portion
  at the top of the Food Pyramid.

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Calories and Energy

• Calories
• 1 gram of fat or oil 9 calories
• 1 gram of carbohydrates or proteins 4 calories
• Thus, fat or oil has 2.25 times as many calories
  per gram as carbohydrates or proteins
• Energy
• Lipids have a high energy content
• This energy is stored and used through the
  formation and metabolism of body fat
• Unused nutrients (carbohydrates, proteins, and
  lipids) are converted into small globules of fat
  that are deposited in adipose tissue
• One pound of this tissue can store or provide
  about 3500 calories of energy
• The energy storage of adipose tissue is
  long-term, unlike the energy storage of glycogen,
  which is short-term

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Calculating Percent Fat

• Percent fat relates the number of fat calories to
  the total number of calories per serving
• Fat calories number of grams of fat listed on
  the label (9 calories/1 gram of fat)
• Percent fat ( fat) (fat calories/total
  calories) 100

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Examples of Calculating Percent Fat

• Example 1 Calculate the fat calories and the
  percent fat for the following label
• Calories/serving 90 cal
• Fat/serving 4 g
• Answer 1
• Fat calories g of fat (9 calories/1 gram of
  fat) 4 g (9 cal/1 g) 36 cal
• Percent fat (fat calories/total calories) 100
  (36 cal/90 cal) 100 40

• Example 2 Calculate the fat calories and the
  percent fat for the following label
• Calories/serving 110 cal
• Fat/serving 6.5 g
• Answer 2
• Fat calories g of fat (9 calories/1 gram of
  fat) 6.5 g (9 cal/1 g) 58.5 cal
• Percent fat (fat calories/total calories) 100
  (58.5 cal/110 cal) 100 53.2

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Saponifiable Lipids Phosphoglycerides

• Phosphoglycerides have two fatty acids a
  phosphate group and an amino alcohol
• They are similar in structure to triglycerides,
  except that the third fatty acid has a phosphate
  group and an amino alcohol
• They are found in cell membranes, where one of
  their important functions is to separate one
  fluid compartment from another
• Phosphoglycerides do this by attracting water
  molecules to its polar portion and by repelling
  water and attracting non-polar substances to its
  nonpolar portion

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The Fluid Mosaic Model of the Structure of a Cell
Membrane

• The fluid mosaic model says that a cell membrane
  has a double layer of phospholipids, which is
  called the lipid bilayer
• The center of this layer has nonpolar hydrocarbon
  tails
• The outer surface has the polar phosphate and
  amino alcohol groups
• The lipid bilayer is a barrier that separates the
  contents of the cell from the surrounding fluids
• It provides selective permeability to NONPOLAR
  molecules, and therefore, proteins are embedded
  in the layer to provide tunnels for POLAR
  substances to pass into the cell

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Saponifiable Lipids Sphingolipids

• Sphingolipids contain the amino alcohol
  sphingosine, instead of glycerol, one fatty acid,
  a phosphate group, and an amino alcohol
• Unlike most saponifiable lipids, they have an
  amide bond instead of an ester bond
• The amide bond can undergo saponification just
  like the ester bond, though, to produce the salt
  of the fatty acid (i.e. soap) as one of the
  products
• Sphingolipids are found in the brain and nerve
  tissue

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Saponifiable Lipids Glycolipids

• Glycolipids contain sphingosine, one fatty acid,
  and a monosaccharide (usually galactose or
  glucose)
• Just like sphingolipids, they have an amide bond
  instead of an ester bond
• Glycolipids are found in the brain and in the
  myelin sheaths of nerves

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Nonsaponifiable Lipids Steroids

• Steroids have a fused-ring structure that is
  called the steroid nucleus
• A variety of steroids are produced by attaching
  various groups to the steroid nucleus
• Cholesterol is the most common steroid
• Estrogen and testosterone are also steroids
• Anabolic steroids are derivatives of testosterone
  that enhance the effects of testosterone
• They enhance strength and muscle mass, but they
  can also cause hypertension, fluid retention,
  liver damage, decreases sperm production, sleep
  disturbances, acne, etc.

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Cholesterol

• Cholesterol is essential for the production of
  hormones, vitamin D, and bile acids
• It is found in brain and nerve tissue, myelin
  sheath, cellular membranes, and the liver
• It can be synthesized from fats, carbohydrates,
  and proteins, or it can be obtained from meats,
  milk, and eggs
• High levels of cholesterol can lead to
  arteriosclerosis, which is when lipid material
  accumulates in the coronary blood vessels and
  thus narrows the coronary arteries
• Cholesterol levels are high if the total plasma
  cholesterol level is greater than 200-230 mg/dL

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Nonsaponifiable Lipids Terpenes

• Terpenes are unsaturated compounds that contain
  isoprene units
• They are found in essential oils and flavorings,
  chlorophyll, and the visual pigments of the
  retina
• Vitamin A is a terpene (see above)