Lipids
• Highly diverse structures
• Unifying property
• Hydrophobic: little to no affinity to water
• Contains hydrocarbons, which form nonpolar covalent bonds
• Do not form polymers
• Biologically important lipids containing molecules:
– Fats
– Phospholipids
– Steroids
Fats
• Structure
– Composed of two different molecules bonded by ester linkage
• fatty acid & glycerol
– - Fatty acid
Hydrocarbon chain with a carboxyl group at one end
– Glycerol
• Three-carbon alcohol
– Each carbon attached to hydroxyl group
LE 5-11a
Fatty acid
(palmitic acid)
Glycerol
Dehydration reaction in the synthesis of a fat
LE 5-11b
Ester linkage
Fat molecule (triacylglycerol)
Properties of Fats
• Hydrophobic
• H2O molecules form hydrogen bonds with each other and EXCLUDE fatty acid
chains-->
Fats separate from H2O (like oil & vinegar)
Fatty acids
variable chain length (often 16-18 carbons)
Saturated fat
- refers to saturated fatty acid chains
- carbons contains maximum number of hydrogens
- results in 100% single bonds (no double bonds)
- more linear, packs tightly to form solid
Tend to be from animals
LE 5-11b
Ester linkage
Saturated or unsaturated?
Fat molecule (triacylglycerol)
LE 5-12a
Butter
Stearic acid
Saturated fat and fatty acid.
Unsaturated fat
-contains unsaturated fatty acids
-carbon-carbon double bonds (>1)
-irregular hydrocarbon conformation
-poor packing
-forms liquids (oils) at room temperature
Tend to be from plants and fish
LE 5-12b
Olive oil
Other liquid fats (unsaturated)?
Oleic acid
cis double bond
causes bending
Unsaturated fat and fatty acid.
Phospholipids
• Structure
– two fatty acids bonded to glycerol through ester linkage
– Phosphate bonded to third hydroxyl group of glycerol
• Fatty acids= Hydrophobic tail
• Phosphate and other groups= hydrophilic head
Draw schematic
LE 5-13
Choline
Phosphate
Glycerol
Fatty acids
Hydrophilic
head
Hydrophobic
tails
Structural formula
Space-filling model
Phospholipid symbol
If many phospholipids were mixed in H2O
into what structures would they self-assemble?
1. Micelle (draw)
- Detergents
2. Bilayer (draw)
-Cell membranes
LE 5-14
Cellular membrane: Phospholipid Bilayer
Hydrophilic
head
Hydrophobic
tails
WATER
WATER
Steroids
• Structure
- Hydrophobic molecules made of 4 fused hydrocarbon rings
• Examples and Diverse Functions
– Cholesterol
• Component of animal cell membranes
• Building block for steroid sex hormones such as
– Estrogen, testosterone, progesterone
• High levels--> contribute to heart disease
Cholesterol
estradiol
testosterone
Pardon me. Did you miss
anything?