Lipids

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Lipids

• L. Scheffler

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Lipids

• Lipids are a group of biomolecules that include
  fats and oils as well as a number of other types
  of molecules.

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Lipids

• Fats and Oils
• Contain H, C, and fewer O than carbohydrates
• Twice the Energy per gram than carbohydrates
• Used for long-term storage energy in animals

Examples Phospholipids steroids carotenoids
(pigments)
http//www.rch.org.au/emplibrary/diabetesmanual/6_
fatsOils.gif
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Fatty Acids

• Long carbon chains (12-38C)
• a carboxyl group (-COOH) on one end
• Carboxyl end (polar) is hydrophilic
• Hydrocarbon chains (non-polar) are hydrophobic

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Common Fatty Acids

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Triglycerides

• Three molecules of fatty acids are attached to
  one molecule of glycerol to form a triester

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Saturated Fatty Acids

• Only single bonds between carbons.
• Considered less healthy, implicated in elevated
  cholesterol synthesis.
• Generally solids, more abundant in fats of animal
  origin.

http//biology.clc.uc.edu/graphics/bio104/fatty20
acid.jpg
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Unsaturated Fatty Acids

• Have at least one carbon to carbon double bond
• Healthier, except trans fats (worst of all)
• Generally Liquids at room temperature
• Found in oils that originate from plants
• Substituting unsaturated for saturated fats
  tends to reduce
• cholesterol levels

http//cretashop.gr/br/imagesbr/pezaoil/popoil.jpg
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Fatty Acids

• Unsaturated fatty acids such as oleic acid
  are liquids at room temperature.
• The double bond creates a kink in the
  chain which decreases the ability of the chains
  to pack together closely.
• As a result the van der Waals forces
  holding the molecules together are weaker

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Saturation of fatty acids

• Saturated fatty acids have carbon chains with
  only C-C single bonds.
• i.e. Lauric Acid CH3-(CH2)10-COOH
• Unsaturated fatty acids have 1 or more CC in
  the carbon chain.
• -- One CC is known as monounsaturated.
• i.e. Oleic Acid
• CH3-(CH2)7CHCH-(CH2)7COOH
• -- More than one CC is known as
  polyunsaturated. i.e Linoleic acid
• CH3-(CH2)4CHCH-CH2-CHCH -(CH2)7COOH

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Saturation of fatty acids

• Most animal fats are saturated fats. They are
  usually solids at room temperature.
• The carbon atoms in the hydrocarbon chain are a
  succession of tetrahedrons that makes it possible
  to pack chains fairly closely together.
• These weak van der Waals attractions over a the
  large surface area result are strong enough to
  sustain the solid state.

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Unsaturated Fatty Acids

• Most vegetable oils are unsaturated They are
  usually liquids at room temperature.
• The presence of one or more CC in the
  hydrocarbon chain results in bond angles of 120o
  instead of the usual 109.5o of the tetrahedrons.
• These kinks in the carbon chain make it harder
  to pack chains fairly close together. The van
  der Waals forces are insufficient to maintain a
  solid state.

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Iodine Index

• Most fats and vegetable oils are mixtures.
  Therefore it is not practical to try to assess
  the molar concentration of each type of fat or
  oil present.

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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 mass of iodine required to react with 100
  grams of fat or oil is called the iodine index

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Iodine Index

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Common Fatty Acids

• Most

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Phospholipids

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

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Phospholipids

• Cell membranes are made of two
• layers of phospholipids (lipid bilayer)
• Head is hydrophilic while the tail is
• hydrophobic

http//personal.tmlp.com/Jimr57/textbook/chapter3/
cms1.htm
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Phospholipids

• Lecithin, an example of a phospholipid, has this
  structure.

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Functions of Phospholipids

• Phospholipids form a significant part of cell
  membranes that protect the cell from the
  intercellular fluids around it.
• The cell membrane must also allow nutrients to
  pass into and out of the cell.
• Phospholipids tend to form bilayers in aqueous
  solutions. 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 which allow the cell membrane to be
  porous.

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Lipid Functions

• Energy storage
• Lipids are highly efficient energy stores
  for most higher animals. Because they have less
  oxygen per molecule, lipids are oxidized more
  slowly, but release more energy.
• Thermal insulation and protection
• Cell Structure
• Lipids, especially Phospholipids, form a
  significant part of cell membranes. They protect
  the cell from the intercellular fluids around it
  and assist in the transport of fluids into and
  out of the cell.