WEEK 3_CHEM 113_Lipids

Introduction to Lipids

Lipids are a diverse group of biological molecules that are insoluble in water but soluble in nonpolar solvents such as chloroform.

COVALENT

Pure Covalent Bond – the electrons in the bond are shared equally due to equal electronegativity between the atoms

Polar Covalent Bond – the electrons in the bond are more attracted to one atom due to unequal electronegativity between the atoms

Trend in Electronegativity

Periodictable low-medium-high

Classification of Lipids

• Saponifiable Lipids: Undergo saponification; contain ester groups.

  • Simple Lipids: Contain fatty acids and an alcohol.

    • Examples include triglycerides and waxes.

  • Complex Lipids: Contain fatty acids, an alcohol, and another component, such as phosphoglycerides.

• Non-saponifiable Lipids: Cannot be saponified; do not contain ester groups. Examples include steroids, eicosanoids, and fat-soluble vitamins.

Roles of Lipids

• Stored forms of energy

• Structural elements of biological membranes

• Helper in cellular messaging

• Provide insulation against low temperatures

Fatty Acids

• Fatty acids are long-chain carboxylic acids, usually nonbranching with an even number of carbon atoms.

  • Hydrophilic carboxyl group under basic conditions (pH 7.4).

  • Hydrophobic long chain of hydrocarbons.

• Classification:

  1. Saturated Fatty Acids: All carbon chains contain single bonds.

  2. Unsaturated Fatty Acids: Contain one or more double bonds, usually in cis configurations.

• Micelles – fatty acids that associate with each other in spherical clusters

  • Important in the transport of insoluble lipids in the blood, and in the actions of soaps.

• Essential Fatty Acids – fatty acids that cannot be synthesized in the body and must be obtained from the diet

  • Use to produce hormone-like substances that regulate blood pressure, blood clotting, blood lipid levels, the immune response, and inflammatory reactions
  

Naturally Occurring Fatty Acids

• Examples Include:

  • Lauric acid (12:0): Melting point 44.2°C, common in laurel plants.

  • Palmitic acid (16:0): Melting point 63.1°C, found in palm trees.

  • Stearic acid (18:0): Melting point 69.6°C, derived from hard fats.

  • Oleic acid (18:1): Melting point 13.4°C, found in olive oil.

• Essential Fatty Acids: Cannot be synthesized in the body; must be ingested.

Saponifiable Lipids

• Triglycerides: Esters composed of three fatty acids connected to glycerol.

• Triglycerides can be broken apart with water and an acid catalyst (hydrolysis), or by digestive enzymes called lipases

• Fats – triglycerides that are solids at room temperature which contains mostly saturated fatty acids and are derived from animals

• Oil – triglycerides that are liquids at room temperature which contains mostly unsaturated fatty acids and are derived from plants or fish

• Hydrolysis: Triglycerides can be broken apart with water and an acid catalyst or digestive enzymes called lipases.

• Saponification Process: triglycerides react with strong bases (NaOH or KOH) to form the carboxylate salts of the fatty acids, called soaps

• NaOH produces a “hard” soap, commonly found in bar soaps; KOH produces a “soft” soap, such as those in shaving creams and liquid soaps

• Hydrogenation – process by which alkenes of unsaturated lipids are converted into alkanes with hydrogen gas (H2 ) and a catalyst (Pt, Ni, or some other metal)

• Waxes – simple lipids containing a fatty acid joined to a long- chain (12-32 carbons) alcohol.

• Often occur in nature as protective coatings on feathers, fur, skin, leaves, and fruits

• Also present in sebum secreted by your sebaceous glands

• Phosphoglycerides – or glycerophospholipids; complex lipids that are major components of cell membranes.

• First two hydroxyl groups of glycerol are where the fatty acids attach

• The third hydroxyl group is where the phosphate group attaches
  
  
  

• Saponifiable Lipids – undergo saponification; contains ester groups

• Simple Lipids – contain fatty acids and an alcohol

  Triglycerides - Waxes

• Complex Lipids – contain fatty acids, an alcohol, and another component

  Phosphoglycerides - Sphingolipids

Non-Saponifiable Lipids

• Steroids: Lipids with a structure of four fused rings. Includes cholesterol, hormones, vitamins.

• Cholesterol: Abundant steroid, essential for cell membranes, precursor to other steroids.

• Eicosanoids: Signaling molecules derived from arachidonic acid, such as prostaglandins affecting smooth muscles.