Mathematics Used in Chemistry

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Chapter 18Lipids
Suggested Problems 9,11,21
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Important Functions of Lipids

• Serve as protective wax coating on some plants
• Energy rich compounds with low densities
• Store energy for plants and animals
• Structural components, especially in cell
  membranes

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Lipids

• Definition biological compound that is insoluble
  in water but soluble in non-polar solvents
• Varied compositions and structures
• Two main classes
• Saponifiable
• Must contain an ester functional group
• Nonsaponifiable

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Classification of Lipids
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Classification of Carbohydrates

• Simple Lipids
• Contain only fatty acid (FA) and alcohol
  components
• Complex
• Contain fatty acid, alcohol, and other components

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Fatty Acids

• Building block of many lipids
• Two parts
• Hydrocarbon tail
• Carboxylic acid group

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Fatty Acids

• Fatty acids form micelles in water
• Polar heads toward the water hydrophobic tails
  group together

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Common Characteristics of Fatty Acids

• Usually straight chains (no branches)
• Usually contain 10-20 carbon atoms
• Usually have an even number of carbons including
  the carbonyl carbon
• Apart from carboxyl group and double bonds,
  usually no other functional groups
• Saturated no double bonds
• Unsaturated 1 or more double bonds

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Unsaturated Fatty Acids

• Double bonds are usually in the cis configuration
• Creates a kink in the chain
• Cannot pack together as closely as saturated FAs

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Question

• Why does the melting point of unsaturated FAs go
  down with increasing number of double bonds?

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(No Transcript)
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Omega Fatty Acids

• Term for identifying the location of the end most
  double bond
• Omega 3 endmost double bond 3 carbons from the
  methyl end of the hydrocarbon chain
• Omega 6 endmost double bond 6 carbons from the
  methyl end of the hydrocarbon chain

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Fats and Oils

• Fats and oils are esters
• Alcohol portion comes from glycerol
• Carboxylic acid portion comes from FAs
• Glycerol has 3 alcohol groups
• Acids attached can be same or different
• This is why fats and oils are called
  triglycerides

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Fats and Oils

• Fats usually triglycerides from animals
• Oils usually triglycerides from plants or fish

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Rxns of Fats and Oils

• Hydrolysis
• Reverse of ester formation
• Acidic conditions
• Catalyzed by enzymes (lipases) in digestive track
• Molecules otherwise left structurally unchanged
• Rxn supplies energy from cellular fat deposits

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Rxns of Fats and Oils

• Hydrolysis

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Rxns of Fats and Oils

• Saponification
• Produces glycerol and SALTS of fatty acids
• Uses a strong base
• Hard soaps Sodium salts
• Cake soap
• Soft soaps Potassium salts
• Shaving cream, liquid soaps

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Rxns of Fats and Oils

• Saponification

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Rxns of Fats and Oils

• Hydrogenation
• Decreases the number of double bonds in the fatty
  acid chains
• React with oils H2 and a catalyst
• Produces cooking shortening and margarine from
  vegetable oils
• Not all double bonds are hydrogenated
• Some double bonds converted to trans configuration

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Rxns of Fats and Oils

• Reaction Summary

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Waxes

• Also esters
• Alcohol portion has long chain (12-32 carbons)
  rather than glycerol
• Water insoluble and not easily hydrolyzed
• Serve as protective coatings

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Phosphoglycerides

• Also called phospholipids
• Complex lipids that are major components of cell
  membranes
• Structure

(or some other alcohol)
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Phosphoglycerides

• Two types
• Lecithins
• Choline is the amino alcohol
• Cells membrane component
• Emusifying agent
• Cephalins
• Ethanolamine or serine as the alcohol
• Found in cell membranes, brain tissue, and
  platelets
• Phosophoglycerides are classified according to
  the amino alcohol used

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Sphingolipids

• Backbone is sphingosine rather than glycerol
• Fatty acids connected through amide linkage
• Also found in cell membranes (particularly in
  brain and nerves)

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Sphingolipids

• Sphingomyelin
• Choline is attached to Sphingosine through
  phosphate group
• Different fatty acids
• Brain/nerve tissue and myelin sheath of nerves

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Sphingolipids

• Glycolipids
• Contain carbohydrate connected through the OH
  group of sphingosine
• Carbohydrate is usually glucose or galactose
• Called cerebrosides because abundant in brain
  tissue

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Membrane Structure

• Most are 60 lipids, 40 proteins
• Lipids are phosoglycerides, sphingomyelin,
  cholesterol
• Lipids are organized in a bilayer
• Fluid mosaic model

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Membrane Structure

• Why do the lipids have two tails?

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Steroids

• Very structurally different from glycerides and
  sphingolipids
• All steroids have 3 6-membered rings and 1
  5-membered ring fused together

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Steroids

• Cholesterol
• Most abundant steroid in the body
• Essential component of cell membranes
• Precursor for other steroids

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Steroids

• Bile Salts
• Produced by liver, secreted by gall bladder, and
  enters small intestine
• Emusifying agent
• Break lipids from food into smaller globules for
  easier hydrolyzation
• Emulsify excess cholesterol to prevent buildup in
  the gall bladder

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Steroid Hormones

• Hormone
• Definition chemical messenger secreted by
  specific glands and carried thoughout the blood
  to a target tissue, where it triggers a
  particular response
• Two types
• Adrenocorticoid hormones
• Sex hormones

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Adrenocorticoid Hormones

• Produced by the adrenal glands
• Two classes
• Mineralocorticoids regulate the concentration of
  ions in bodily fluids
• Aldosterone increases absorption of Na, Cl-
• Glucocorticoids enhance carbohydrate metabolism
• Cortisol increases glucose and glycogen
  concentrations in the body

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Sex Hormones

• Two types
• Androgens produced by the testes
• Testosterone
• Estrogens and Progesterone produced by the
  ovaries
• Estradiol and estrone are the most important
  estrogens

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Prostaglandins

• Cyclical compounds made from arachidonic acid
• Involved in many bodily processes (like hormones)
• Involved in
• Reproductive phases
• Blood clotting
• Inflammation and fever
• Treat medical conditions
• Relax muscles around bronchial tubes (asthma)
• Decrease gastic sectretions (peptic ulcers)