Lipids

Characteristics

• Contain C, H, and O (like carbohydrates) but fewer O atoms

• Due to the abundance of C-H bonds, lipids are hydrophobic/largely non-polar

• Functions of lipids: to store energy (C-H bonds are very high energy and less accessible to cells), insulation, protection, and have functions in the cell membrane

• Major types include triglycerides, fatty acids, phospholipids, steroids

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Fatty Acids

• Chain of usually 4 to 24 carbon atoms

• Carboxyl functional group on one end and a methyl group on the other

• Saturated fatty acid - carbon atoms saturated with hydrogen

• Unsaturated fatty acid - contains C=C bonds that could bond with more hydrogens

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Triglycerides

• Composed of one glycerol molecule and three fatty acids

• The bond between the hydroxyl group on the glycerol and the carboxyl group on the fatty acid is called an ester linkage

• Triglycerides containing saturated fatty acids are often solid at room temp (e.g. butter)

• Triglycerides containing unsaturated fatty acids are often liquid (e.g. canola oil)

Triglyceride Synthesis

• Three fatty acids bonded to glycerol by dehydration synthesis

• Triglycerides are called neutral fats

• fatty acids bond with their carboxyl ends, therefore, they are no longer acidic

Phospholipids

• Lipids that make up the cell membrane

• Composed of fatty acid tails, a glycerol molecule, a phosphate functional group, and an “R” group (different atoms)

• The “head” (phosphate & R group) of the phospholipid is polar, while the “tail” (fatty acids) are non polar.

• This causes phospholipids to form a bilayer (hydrophobic tails face each other and hydrophilic heads face the aqueous solution) in aqueous environments

Other Lipids

• Steroids: made of 4 carbon rings.Cholesterolis an example which functions in the nervous system, as part of the cell membrane, and derivatives such as testosterone & estrogen

• Waxes: made of long carbon chains. Examples includebeeswax, earwax, andcovering in plants.