Describe the unique properties building-block molecules and biological importance of the three important groups of lipids fats phospholipids and steroids?
III. Lipids are diverse group of hydrophobic molecules, all
hydrophobic; includes waxes and pigments not discussd A. Fats - not
polymers, large molecules assembled from smaller molecules -
glycerol and fatty acids 1. glycerol = alcohol w/ 3 C, each with a
OH group 2. fatty acid = long C skeleton, 16-18 C long (fig 5.11)
a. carboxyl group at end b. long chain of hydrocarbons - C-Hbonds
are nonpolar, producing hydrophobic molecule c. 3 fatty acids join
to the carbon skeleton, making a triglyceride, aka triglycerol d.
fatty acids attached to the chain can be the same or different e.
if there are no double bonds btn C, chain is straight - saturated
fatty acid - solid =fats f. if double bonds occur, chain is kinked-
unsaturated - will be liquid = oils g. cis bonds vs. trans bonds in
hydrogenated products 1. trans fats in hydrogenated products may
contribute more to atherosclerosis than saturated fats h. fat is
very useful - a gram of fat stores more than 2x as much energy as a
gram of polysac 1. compact storage for animals on the move (Plants
don't have to move) 2. storage, warmth and cushioning B.
Phospholipids -similar to fat, but only 2 fatty acids 1. 3rd
hydroxyl group of glycerol attaches to negatively charged phosphate
group (Fig. 5.13) a. other small charged molecules can attach to
phosphate group to form phospholipids 2. head is hydrophilic, tail
is hydrophobic (fig 5.14) a. in water, phospholipids self assemble
into bilayers to shield hydrophobic portions from H2O 3. cell
membranes are made of this, form a boundary btn cell and
environment that is semipermeable C. Steroids - lipids w/ 4 fused
rings for C skeleton (f.g 5.15) 1. functional groups vary 2.
cholesterol a. common in cell membranes b. precurser of other
steroids, eg. sex hormones and other hormones c. cholesterol is
important, too much is bad
SOURCE: www.ltcconline.net/kloss/bio101/ch5.doc