Fats and Oils: Fatty Acids and Esters

Waxes

• Waxes are composed of fatty acids and higher molecular weight monohydric alcohols.

Fats

• Fats are esters of fatty acids with glycerol.
• They are solid at room temperature, but some are liquid at room temperature and are known as oils.
• The physical state of fats depends on the nature of the fatty acids.
• Fats are rich in saturated fatty acids, while oils are rich in unsaturated fatty acids.
• Fatty acids can form mono-, di-, or tri-esters with the alcohol groups of glycerol.

Neutral Fats (Triacylglycerols or Triglycerides)

• Neutral fats are also known as triacylglycerols (TAG) or triglycerides (TG).
• They are esters of the trihydricalcohol, glycerol, with fatty acids.

Compound Lipids

• Compound lipids include:
  • Phospholipids
  • Glycolipids
  • Lipoproteins

Phospholipids

• Phospholipids are lipids conjugated with phosphoric acid.
• Functions of phospholipids:
  • Structure component of cell membrane and nervous system
  • Formation of surface layer of lipoprotein
  • Dipalmityl lecithin acts as a lung surfactant
  • Signal transduction of hormones
• There are two classes of phospholipids:
  • Glycerophospholipids (phosphoglycerides)
  • Sphingolipids

Glycerophospholipids

• Glycerophospholipids are the major lipid components of biological membranes.
• They are derivatives of phosphatidic acid.
• Examples of glycerophospholipids:
  • Phosphatidic acid
  • Lecithin (phosphatidylcholine)
  • Cephalin
  • Phosphatidyl serine
  • Cardiolipin

Phosphatidic Acid

• Phosphatidic acid is made up of one glycerol molecule to which two fatty acid residues are esterified to carbon atoms 1 and 2.
• The 3rd hydroxyl group is esterified to a phosphoric acid.
• It is the parent of all glycerophospholipids.

Lecithin (Phosphatidylcholine)

• Lecithin is composed of a choline head group and glycerophosphoric acid, with a variety of fatty acids.
• Usually, one fatty acid is saturated and the other is unsaturated.

Lung Surfactants

• Dipalmityl-lecithin: it contains two molecules of palmitic acid and acts as a lung surfactant.

Cephalin

• Cephalin differs from lecithins only in that choline is replaced by ethanolamine or serine.
• Sources: brain tissues
• Enters in the formation of cell walls and thromboplastin.

Phosphatidyl inositol

• Phosphatidyl inositol: phosphatidic acid + inositol.

Cardiolipin

• Cardiolipin: two molecules of phosphatidic acid linked together by one molecule of glycerol.

Sphingophospholipids

• Sphingophospholipids contain amino alcohol sphingosine instead of glycerol.

Glycolipids

• Glycolipids are made up of a fatty acid, an alcohol, and some carbohydrates.

Lipoproteins

• Lipoproteins are made up of some lipids combined with specific proteins.

Unsaturated Fatty Acids

• Unsaturated fatty acids contain one or more double C=C bonds.
• Characteristics:
  • Nonlinear chains do not allow molecules to pack closely
  • Few interactions between chains
  • Low melting points
  • Liquids at room temperature

Subclassification of Unsaturated Fatty Acids

• Mono-unsaturated: having a single double bond
• Polyunsaturated: with 2 or more double bonds

Polyunsaturated Fatty Acids

• Polyunsaturated fatty acids are essential fatty acids, which cannot be synthesized by the body and must be supplied in the diet.
• Examples:
  • ω3 (omega 3) family - Linolenic acids
  • ω6 family - Linoleic and Arachidonic acids

Clinical Significance of Polyunsaturated Fatty Acids

• Formation of healthy cell membranes
• Proper development and functioning of the brain and nervous system
• Enter in the composition of phospholipid (a type of compound lipid)
• Causing esterification of cholesterol (free cholesterol), so decrease atherosclerosis (CHD)
• Production of hormone-like substances called Eicosanoids (important for inflammation reaction and allergic reaction)