Introduction to Lipids

Introduction to Lipids

• Lipids are biological compounds that are insoluble or sparingly soluble in water.
• They include lipid-soluble vitamins (A, E, D, K).
• Lipids serve as major energy reserves in the body, primarily as triacylglycerols (triglycerides).
• They provide 9 kcal of energy per gram.
• Lipids insulate body organs.
• Lipids are structural components of cell membranes.
• Lipids are intercellular chemical messengers and aid in lipid solubilization.

Classification of Lipids Based on Structure

• Simple Lipids: Esters of fatty acids with various alcohols.

  • Natural fats and oils (triacylglycerols): Naturally occurring fats and oils.
  • Waxes:
    • True waxes: Cetyl alcohol esters of fatty acids.
    • Other types of waxes.
  • Cholesterol Esters
  • Vitamin A Esters
  • Vitamin D Esters

• Compound Lipids: Esters of fatty acids with alcohol plus other groups.

  • Phospholipids: Contain phosphoric acid and a nitrogenous base.
  • Sphingolipids: Contain an amino alcohol (sphingosine) and some include glycolipids and cerebrosides.
  • Sulfolipids: Contain a sulfate group.
  • Lipoproteins: Lipids attached to plasma/other proteins.
  • Lipopolysaccharides: Lipids attached to polysaccharides.

Derived Lipids

• Hydrolytic products of simple and compound lipids
  • Saturated and unsaturated fatty acids: Fatty acids that are saturated, or have one or more carbon-carbon double bonds
  • Monoacylglycerols and diacylglycerols: glycerols that have one or two fatty acids attached.
  • Alcohols (β-carotenoid ring): like β-carotene

Miscellaneous Lipids

• Aliphatic HC: In liver fat and certain hydrocarbons in beeswax and plant waxes.
• Squalene: Found in shark and mammalian liver as well as human sebum.
• Vitamins A, D, E, and K: Fat-soluble vitamins.

Lipids with Fatty Acids

• Waxes: Protective coatings.
• Triacylglycerols: Energy storage.
• Phospholipids: Components of cell membranes.
• Sphingolipids: (structural) components of cell membranes.
• Steroids: (cholesterol) act as messengers.
• Bile acids: Assist in lipid emulsification.

Lipids without Fatty Acids

• Steroids: Have a fused ring system, including cholesterol.
• Cholesterol: Crucial for animal cells and precursor of other steroids.
• Bile salts: Help digest and absorb dietary fats.
• Prostaglandins: Derived from arachidonic acid. Play a role in pain, fever, and other bodily functions.
• Leukotrienes: Involved in allergic and inflammatory responses.
• Lipoproteins: Complexes of lipids and proteins required for transporting lipids in the blood.

Fatty Acids

• Naturally occurring monocarboxylic acids.
• Typically long-chain (10-20 carbon atoms).
• Often saturated or unsaturated, with double bonds.
• Saturated fatty acids (SFAs): Pack closely and have high melting points (solids).
• Monounsaturated fatty acids (MUFAs): Contain one double bond.
• Polyunsaturated fatty acids (PUFAs): Contain more than one double bond and often have low melting points (liquid).

Physical Properties of Fatty Acids

• Solubility in water varies with the length of the carbon chain and pH.
• Saturated fatty acids have higher melting points than unsaturated fatty acids.
• Degree of unsaturation affects the melting point.

Transport Across Membranes

• Membranes restrict ion and polar molecule movement.
• Mechanisms for transporting across membranes include simple diffusion, facilitated diffusion, and active transport.

Cell Membrane and Related Structures

• Membranes: Semi-permeable Barriers
• Micelles: Spherical structures, with hydrophobic cores and hydrophilic surfaces; key in the digestion of fats.
• Bilayers: Phospholipid bilayers have polar (hydrophilic) heads facing the aqueous environment, and non-polar (hydrophobic) tails facing each other.

Fluid Mosaic Model

• Plasma membranes have a fluid consistency at body temperature.
• Proteins and other substances can move across the membrane.
• Cholesterol makes the membrane stable and prevents it from solidifying.

Triacylglycerols (TAGs)

• Triacylglycerols are triesters of fatty acids with glycerol.
• Fats (saturated) are typically solid at room temperature, while oils (unsaturated) are liquid.

This quiz covers the basics of lipids, including their structure, function, and classification. Explore the different types of lipids such as simple and compound lipids, their biological roles, and their significance in energy storage and cellular structure. Test your knowledge on lipid-soluble vitamins and their functions.