Lipids

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Lipids

• L. Scheffler
• IB Chemistry 1-2
• Lincoln High School

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Lipids

• Lipids are organic molecules with long
  hydrocarbon chains that are soluble in non-polar
  organic solvents
• Lipids are generally divided into three classes
• 1.Triglycerides Fats and Oils
• 2. Phospholipids lecithin
• 3 Steroids -- Cholesterol

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Fats and Oils

• Fats and oils are triesters formed from the
  condensation reaction of glycerol
  (1,2,3,propanetriol) with long chain fatty acids
• Example

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Fats and Oils

• Fats are generally solids at room temperature,
  while oils are usually liquids
• Fats contain saturated hydrocarbon chains
• Oils contain unsaturated hydrocarbon chains, with
  at least 1 CC. Frequently there are several
  CC. They are known as polyunsaturated.

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Fatty Acids

• Stearic acid and linoleic acid have the same
  number of carbon atoms but very different melting
  points.

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Common Fatty Acids
Name Formula Formula Source Source
Saturated Fatty Acids Saturated Fatty Acids Saturated Fatty Acids Saturated Fatty Acids Saturated Fatty Acids
Lauric Acid Lauric Acid CH3-(CH2)10-COOH Coconut Oil Coconut Oil
Palmitic Acid Palmitic Acid CH3-(CH2)14-COOH Palm Oil Palm Oil
Stearic Acid Stearic Acid CH3-(CH2)16-COOH Animal and vegetable fats Animal and vegetable fats
Arachidic Acid Arachidic Acid CH3-(CH2)18-COOH Peanut Oil Peanut Oil
Unsaturated Fatty Acids Unsaturated Fatty Acids Unsaturated Fatty Acids Unsaturated Fatty Acids Unsaturated Fatty Acids
Oleic Acid CH3-(CH2)7CHCH-(CH2)7COOH CH3-(CH2)7CHCH-(CH2)7COOH CH3-(CH2)7CHCH-(CH2)7COOH Corn Oil
Linoleic Acid CH3-(CH2)4 CHCH-CH2-CHCH (CH2)7COOH CH3-(CH2)4 CHCH-CH2-CHCH (CH2)7COOH CH3-(CH2)4 CHCH-CH2-CHCH (CH2)7COOH Linseed Oil
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Differences in Melting Points

• The carbon atoms in the hydrocarbon chain form a
  succession of tetrahedrons
• This regular tetrahedral arrangement of carbon
  atoms makes it possible for it to pack with
  parallel chains fairly closely together
• Although the attractions between the chains are
  only the rather weak van der Waals attractions
  the large surface area in the long carbon chains
  groups result in attractive forces that are
  strong enough to sustain a solid state

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Unsaturated Fatty Acids

• The presence of the CC in the unsatruated fatty
  acid chain changes the bond angle from about 109
  oC to around 120 oC.
• This kink in the carbon chain keeps the fatty
  acids from packing as closely together.
• As a result the van der Waals forces are weaker
  and less energy is required to separate them.

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Saturated and Saturated Fats and Nutrition

• Saturated and unsaturated fats are terms most
  commonly used in the context of nutrition.
• Most animal fats are saturated fats. They are
  usually solids at room temperature.
• Vegetable oils are more unsaturated. They are
  liquids at room temperature.
• Oils with one CC double bond per fatty acid
  chain are called monounsaturated oils
• Oils with more than one CC double bond per fatty
  acid chain are called polyunsaturated oils.

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Hydrogenated Fats and Oils

• Unsaturated oils can be hydrogenated to form
  solid, saturated fats by the reaction with
  hydrogen gas in the presence of nickel or
  platinum as a catalyst.
• Margarine is an example of a hydrogenated oil.

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The Iodine Index

• The degree of unsaturation can be measured by
  measuring the amount of iodine that can react
  with the unsaturated fat or oil. Each mole of
  CC requires one mole of I2 to react.
• The haloalkane chain is nearly colorless
  Therefore unsaturated hydrocarbon chains will
  destroy purple brown color of iodine solutions as
  long as there are CC bonds present.

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Iodine Index of Common Fats/ Oils
Oil or fat Percent saturated fats Percent of monounsaturated fats Percent of polyunsaturated fats Iodine Index
Butter fat 67 29 4 34
Beef Tallow 52 44 4 50
Olive Oil 15 75 10 81
Peanut Oil 18 49 33 93
Canola Oil 7 62 31 130
Sunflower oil 10 13 77 125
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Essential Fatty Acids

• Most naturally occuring fats are a mixture of
  saturated, monounsaturated and polyunsaturated
  fatty acids
• Essential fatty acids are those that the body
  cannot synthesize on its own.
• They must be acquired from the foods we eat.

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Essential Unsaturated Fatty Acids

• w-6 linoleic acid is an example of an
  essential fatty acid. It is a cis isomer. The
  w-6 indicates that there is a CC on the 6th
  carbon from the end of the carbon chain

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Essential Unsaturated Fatty Acids

• w-3 linolenic acid is another example of an
  essential fatty acid. It is a cis isomer. The
  w-3 indicates that there is a CC on the 3rd
  carbon from the end of the carbon chain

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Trans Fatty Acids

• When fatty acids are made synthetically by
  partially hydrogenating other polyunsaturated
  fatty acids, some trans isomers may be formed.
• Trans fatty acids are found in fried foods and in
  some margarines.

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Trans Fatty Acids

• Trans fatty acids are generally considered
  undesirable since they increase the formation of
  LDL Cholesterol and hence the risk of heart
  disease.

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Fat Metabolism

• Fats metabolism occurs more slowly than
  carbohydrates metabolism but fats provide more
  energy than carbohydrates.
• Fats require greater degree of oxidation to
  become CO2 and H2O than carbohydrates because
  carbohydrates already have one oxygen for every
  carbon atom
• The number of oxygen molecules needed to oxidize
  a fat is greater than for carbohydrates., The
  oxidation of fats takes longer, but it also
  generates more energy.

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Hydrolysis of Fats

• In the body triglycerides, fats and oils, are
  hydrolyzed to fatty acids by the action of
  enzymes known as lipases

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Hydrolysis of Fats
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Phospholipids

• A phospholipid has one of the three carbon chains
  of a triglyceride is replaced with a more polar
  phosphate-containing group.

Four parts of a phospholipid
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Phospholipids

• In a phospholipids are one of the essential
  components of cell membranes.
• Phosphatidyl Choline, an example of a
  phospholipid, has this structure

• Phosphatidyl choline is a major component of
  lecithin found in egg yolk,

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Phospholipid Functions

• Phospholipids form a significant part of cell
  membranes.
• The cell membrane must protect the cell form the
  intercellular fluids around it. At the same time
  it must allow cell nutrients to enter the cell
  and waste products to leave.
• Phospholipids tend to form
• bilayers in aqueous solutions.

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Phospholipid Functions

• The polar heads interface with water and the
  non-polar tails are attracted to non-polar
  tissues.
• The larger phospholipids can open and close to
  form vesicles. It is believed that this behavior
  is important to the functioning of the porous
  cell membranes

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Cholesterol

• Cholesterol has the characteristic four ring
  structure that is common to all steroids.
• Cholesterol exists in esterified form in fatty
  acids and in a free form.
• Cholesterol is created by the liver, but is also
  available through food.

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Cholesterol Functions

• Cholesterol is the most common, important and
  necessary steroid in the human body.
• It is component of all tissues and is found in
  the blood, brain and the spinal cord.
• It also acts as a building block to create other
  steroids such as sex hormones and adrenocorticoid
  hormones as well as essential substances such as
  vitamin D.

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LDL and HDL

• Cholesterol is transported around the body by
  lipoproteins.
• Low density lipoproteins (LDL) range from 18-25nm
• LDL transport cholesterol to the arteries where
  it can build up and cause cardiovascular disease
• LDL result from saturated fats, especially lauric
  (C12), myristic (C14) and palmitic (C16) acids.
• High density lipoproteins (HDL) are smaller,
  ranging from 8-11 nm.
• HDL can remove cholesterol from the arteries and
  transport it back to the liver.

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Lipid Functions in the Body

• Energy storage Lipids are highly efficient
  energy stores for most higher animals. Fats are
  stored in the adipose tissues. Because they have
  less oxygen per molecule, lipids are oxidized
  more slowly, but release more energy.
• Thermal insulation and protection Fats provide
  thermal insulation for the body.
• Cell Structure Lipids, especially phospholipids,
  form a significant part of most cell membranes.
  They protect the cell from the intercellular
  fluids around it and play an important role in
  the transport of fluids into and out of the cell.

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The end
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