LIPIDS

Introduction to Lipids

• Definition: Organic compounds found in living organisms that are insoluble in water but soluble in nonpolar organic solvents.

Types of Lipids

• Structural Diversity: Lipids can vary in structure; some are esters, amides, or alcohols; acyclic, cyclic, or polycyclic.

• Major Types of Lipids:

• Fatty Acids

• Triglycerides

• Phospholipids

• Steroids

• Waxes

• Sphingolipids

• Prostaglandins

Classification of Lipids

• Hydrolyzable Lipids: Can be broken down into smaller molecules via hydrolysis (e.g., triglycerides, phosphoglycerides).

• Non-Hydrolyzable Lipids: Cannot be cleaved into smaller units by hydrolysis (e.g., steroids, waxes).

Structure of Fatty Acids

• Building Blocks: Naturally occurring carboxylic acids, typically 12-20 carbon atoms long, with a carboxyl group (-COOH) at one end and a methyl group (-CH3) at the other.

• Amphipathic Nature: Fatty acids have a hydrophilic (water-attracting) carboxyl head and a hydrophobic (water-repelling) tail.

Types of Fatty Acids

1. Saturated Fatty Acids (SFAs):

   • No double bonds (C=C)

   • Solid at room temperature

   • High melting point

   • Examples: Palmitic acid, stearic acid

2. Unsaturated Fatty Acids (UFAs):

   • Contain one or more double bonds

   • Liquid at room temperature

   • Lower melting point

   • Categories include:

     • Monounsaturated Fatty Acids (MUFAs): One double bond (e.g., oleic acid)

     • Polyunsaturated Fatty Acids (PUFAs): Two or more double bonds (e.g., linoleic acid)

Omega - n fatty acids

• where n is the carbon at which the first double bond occurs in the carbon chain, beginning at the end of the chain that contains the CH3 group (omega group).

Fatty Acid Nomenclature

• Fatty acids can be described by (example):

  • systematic name: cis-9-octadecenoic acid

  • common name: oleic acid

  • delta (Δ) numbering of carbon skeleton: 18:1Δ9

    • describes location of the first carbon of the alkene in relationship to the carbonyl carbon

  • omega (ω) numbering of carbon skeleton: 18:1ω9

    • describes location of the first carbon of the alkene in relationship to the terminal methyl

Fatty Acid Isomers

• Cis vs. Trans Isomers:

• Cis: Natural form found in most unsaturated fatty acids, with hydrogen atoms on the same side of the double bond.

• Trans: Produced during partial hydrogenation, with hydrogen atoms on opposite sides, found in some processed foods.

Biological Roles of Lipids

• Energy Storage: Lipids provide a significant energy reservoir.

• Insulation: They help reduce heat loss and protect organs.

• Membrane Structure: Major components of cellular membranes, aiding in cell integrity.

• Hormonal Regulation: Serve as precursors for steroid hormones and signaling molecules.

• Cofactors: Participate in enzyme reactions as cofactors (e.g., coenzyme Q).

• Vitamins: Include fat-soluble vitamins A, D, E, K, which are essential for various biological processes.

Hydrogenation

• A commercial process used to reduce C=C bonds in unsaturated fatty acids to generate saturated fatty acids and trans fatty acids.

• Trans fats produced commercially are added to processed foods.

• Dairy products contain trans fats produced by bacteria in the rumen of cows

ESSENTIAL FATTY ACIDS (EFA)

• Fatty acids that the human body cannot synthesize in sufficient amounts and must be obtained through diet.

• Essential FA: linoleic acid and linolenic acid.

• Importance: proper membrane structure; serve as starting materials for the production of several biochemically important longer-chain omega-6 and omega-3 acids.

• Linoleic acid is converted into arachidonic acid, which is important for regulating blood pressure and blood clotting.

• Linolenic acid is turned into eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are vital for brain health and development, as well as for eye function.

Triglycerides (ENERGY-STORAGE LIPIDS)

• Structure: Composed of glycerol and three fatty acids (triester).

• Function: Main energy storage form in humans and animals, and is used as a carrier for fat-soluble compounds.

Phospholipids (COMPLEX LIPIDS)

• Role in Cell Membranes: Form the bilayer structure of cell membranes, comprising phosphate heads (hydrophilic) and fatty acid tails (hydrophobic).

• Examples: Phosphatidylcholine, a common phospholipid in cell membranes.

Steroids

• Structure: Characterized by a fused ring system.

• Examples: Cholesterol, crucial for membrane structure and as a precursor for steroid hormones.

Eicosanoids (MESSENGER LIPIDS)

• oxygenated C20 fatty acid derivative that functions as a messenger lipid.

• Types: Prostaglandins, thromboxanes, leukotrienes.

• Function: Involved in inflammation, pain regulation, blood pressure control, reproductive functions, and regulation of the sleep/wake cycle

• Precursor: Arachidonic acid (20:4 fatty acid).

Lipoproteins (Carriers of Cholesterol)

• Function: Transport cholesterol and fats in the bloodstream.

• HDLs (High-Density Lipoproteins): Carry cholesterol back to the liver.

• LDLs (Low-Density Lipoproteins): Deliver cholesterol from the liver to tissues.

Steroid Hormones

• Steroid hormones are a type of hormone made from cholesterol. Hormones are substances produced by glands that help different parts of the body communicate with each other.

  1. Sex hormones: These control reproduction and the development of secondary sex characteristics (like breast development in females and facial hair in males).

  2. Adrenocorticoid hormones: These help regulate many important processes in the body, such as metabolism and stress response.

Anabolic Steroids

• Some bodybuilders use anabolic steroids to increase muscle mass.

• Long-term or excessive use can cause many health problems, including high blood pressure, liver damage, and cardiovascular disease.

Bile Acids (Emulsification Lipids)

• Bile acids are substances derived from cholesterol that help break down fats in the digestive system. They act as emulsifiers, which means they can mix water-insoluble fats with water, allowing them to be more easily digested.

• it is made by the liver, stored in the gallbladder, and released into the small intestine when we eat to help with fat digestion.

Essential Fatty Acids

• Importance: Linoleic acid and linolenic acid are vital for maintaining membrane structure and synthesizing longer-chain fatty acids.

• Health Implications: PUFAs like EPA and DHA have roles in cognitive health and inflammatory responses.

Fat-Soluble Vitamins

1. Vitamin A (retinol): Crucial for vision and immune function.

   • from fish liver oils and dairy products; synthesized from β-carotene, the orange pigment in carrots.

   • deficiency of vitamin A causes night blindness, as well as dry eyes and skin.

2. Vitamin D: Helps in calcium regulation, deficiency leads to bone issues.

   • Vitamin D3 is the most abundant; helps regulate both calcium and phosphorus metabolism.

   • deficiency of vitamin D causes rickets, a bone disease characterized by knock-knees, spinal curvature, and other deformities.

3. Vitamin E (antioxidant): Antioxidant that protects cell membranes.

   • a group of structurally similar compounds, the most potent being α-tocopherol; protects unsaturated side chains in fatty acids from oxidation

   • deficiency of vitamin E causes numerous neurologic problems.

4. Vitamin K (phylloquinone): Necessary for blood clotting processes.

   • regulates the synthesis of prothrombin and other proteins needed for blood to clot.

   • deficiency of vitamin K leads to excessive and sometimes fatal bleeding because of inadequate blood clotting.