Lipids Overview and Functions

Study Notes

Heterogeneous group of organic compounds containing carbon, hydrogen, and oxygen.
May also contain phosphorus, nitrogen, and sulfur.
Water-insoluble (hydrophobic)
Highly soluble in non-polar solvents like benzene, chloroform, and ether.

Important dietary constituents, providing more energy per gram than carbohydrates and proteins.
Storage form of energy (triglycerides).
Thermal insulator in subcutaneous tissues and around organs.
Component of cell membranes
Source of fat-soluble vitamins (A, D, E, K).
Electric insulators in neurons.
Metabolic regulators (steroid hormones and prostaglandins).

Simple Lipids:
- True fats: Esters of fatty acids with glycerol.
- Waxes: Esters of fatty acids with higher molecular weight monohydric alcohol.
Complex Lipids (Compound Lipids):
- Esters of fatty acids with alcohol and an additional group.
- Phospholipids: Contain fatty acids, alcohol, and phosphoric acid.
- Glycolipids: Contain fatty acids, alcohol, and carbohydrates.
Derived Lipids:
- Hydrolysis products of simple and compound lipids.
- Fatty Acids: Aliphatic monocarboxylic organic acids, primarily obtained from simple lipid hydrolysis.
- Glycerol: A three-carbon alcohol.
- Alcohols (other than glycerol): Examples include cholesterol and steroids.
- Steroids: Lipids related to fatty acids, important for cell function and hormonal regulation.
- Carotenoids: Pigments with antioxidant properties.
- Fat-soluble Vitamins: Vitamins A, D, E, and K.

Definition: Aliphatic monocarboxylic organic acids derived from simple lipid hydrolysis.
Structure: Consists of a hydrophobic hydrocarbon chain with a terminal carboxyl group (COOH) (hydrophilic) and a methyl group (CH3) at the other end.
Numbering Systems:
- Δ-numbering: Count carbons starting from the carboxyl group.
- Greek lettering: Assign Greek letters to carbon atoms starting from the carboxyl group.
- ω-numbering: Count carbons starting from the methyl group.
Even Number of Carbons: Most fatty acids in nature contain an even number of carbon atoms.

Chain Length:
- Short-chain fatty acids (SCFAs): 2-10 carbons, easily absorbed without bile salts.
- Long-chain fatty acids (LCFAs): More than 10 carbons, require bile salts for absorption.
Saturation:
- Saturated fatty acids (SFAs): No double bonds, densely packed, solid at room temperature.
- Unsaturated fatty acids (UFAs): One or more double bonds, kinked structure, liquid at room temperature.
- Monounsaturated fatty acids (MUFAs): One double bond, example: Oleic acid (ω9, 18:1).
- Polyunsaturated fatty acids (PUFAs): More than one double bond, examples: Linoleic acid (ω6, 18:2), Linolenic acid (ω3, 18:3), Arachidonic acid (ω6, 20:4).
Biological Classification:
- Essential fatty acids: Cannot be synthesized by the body, examples: Linoleic acid (ω6), Linolenic acid (ω3).
- Relatively essential fatty acid: Can be synthesized from linoleic acid, example: Arachidonic acid (ω6).
- Non-essential fatty acids: Can be synthesized by the body.

Excessive fat deposits: Cause obesity. Truncal obesity is a risk factor for heart attacks.
Abnormalities in cholesterol and lipoprotein metabolism: Lead to atherosclerosis and cardiovascular diseases.
Diabetes mellitus: Deranged metabolism of fatty acids and lipoproteins, leading to ketosis.
Short-chain fatty acids: Absorbed without bile salts.
Long-chain fatty acids: Require bile salts for absorption.
Saturated fatty acids: Solid at room temperature, contribute to higher LDL cholesterol levels.
Unsaturated fatty acids: Liquid at room temperature, contribute to lower LDL cholesterol levels.
Trans fats: Artificially created by hydrogenation, potentially harmful to health, including heart disease and altered brain function.
Essential fatty acids: Important for growth, development, membrane formation, and synthesis of inflammatory mediators.