Lipids

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Lipids

• Does not include polymers only grouped together
  based on trait of little or no affinity for
  water
• Hydrophobic
• Hydrophobic nature is based on molecular
  structure consist mostly of hydrocarbons

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Highly varied group

• Smaller than true polymeric macromolecules
• Insoluble in water, soluble in organic solvents
• Serve as energy storage molecules
• Can act as chemical messengers within and between
  cells
• Include waxes and certain pigments
• Focus will be on fats, phospholipids, and steroids

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Fats -- Triglycerides

• Made of two kinds of smaller molecules glycerol
  and fatty acids (one glycerol to three fatty
  acids)
• Dehydration synthesis hooks these up 3 waters
  produced for every one triglyceride
• Glycerol is an alcohol with three carbons, each
  one with a hydroxyl group
• Fatty acid has a long carbon skeleton at one end
  is a carboxyl group (thus the term fatty acid)
  the rest of the molecule is a long hydrocarbon
  chain
• The hydrocarbon chain is not susceptible to
  bonding, so water H-bonds to another water and
  excludes the fats

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Figure 5.10 The synthesis and structure of a
fat, or triacylglycerol
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Saturated vs. Unsaturated Fats

• Refers to the structure of the hydrocarbon chains
  of the fatty acids
• no double bonds between the carbon atoms of
  the chain means that the max of hydrogen atoms
  is bonded to the carbon skeleton saturated
  THESE ARE THE BAD ONES!!! they can cause
  atherosclerosis (plaque develop, get less flow of
  blood, hardening of arteries)
• if one or more double bonds is present, then
  it is unsaturated (and these tend to kink up and
  prevent the fats from packing together)

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Figure 5.11 Examples of saturated and
unsaturated fats and fatty acids 
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Fat vs. Oil

• Most animal triglycerides are saturated
• Ex. Lard, butter
• These are solid at room temperature -- fat
• Plants and fish have unsaturated triglycerides,
  so are liquid at room temp oil
• Ex. Vegetable oil, sunflower oil, cod
  liver oil

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Figure 5.11x Saturated and unsaturated fats and
fatty acids butter and oil
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Are lipids Bad?

• Major function is energy storage
• Ex. Gram of fat stores more than TWICE the
  energy of a gram of polysaccaharide
• Since plants are immobile, bulky storage of
  starch is okay animals needs mobility, so
  compact reservoir of fuel (fat or adipose tissue)
  is better
• Adipose tissue provides cushioning for organs and
  insulation for body

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Phospholipids

• Have only two fatty acid tails
• Third hydroxyl group of glycerol is joined to a
  phosphate group (negatively charged)
• Are ambivalent to water tails are hydrophobic,
  heads are hydrophilic
• When added to water, phospholipids self-assemble
  into aggregates
• Ex. micelles phospholipid droplet with
  the phosphate head on the outside
• At cell surface, get a double layer arrangement
  phospholipid bilayer

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Figure 5.12 The structure of a phospholipid
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Figure 5.12x Phospholipid
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Figure 5.13 Two structures formed by
self-assembly of phospholipids in aqueous
environments   
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Steroids

• Characterized by carbon skeleton consisting of
  four fused rings
• Differences depend on the functional groups
  attached to the ring ensemble
• Cholesterol found in cell membranes of animals,
  is a precursor from which other steroids may be
  synthesized (but if is found in high levels in
  the blood, contributes to atherosclerosis
• Many hormones are steroids sex hormones

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Figure 5.14 Cholesterol, a steroid    
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Figure 5.14x Cholesterol    
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Tests for Presence of Lipids

• Translucence Test lipids leave a
  semi-transparent spot on brown paper
• Solubility Test Lipids are insoluble in water,
  but soluble in an organic solvent such as alcohol
  or lighter fluid
• Sudan III Test Lipids will stain red in the
  presence of Sudan III