Lipids and Fatty Acids Overview

Fatty acids are aliphatic single-chain carboxylic acids created by hydrolyzing fats and oils.
They have the general formula R-(CH2)n-COOH.
Usually, they have a straight chain with an even number of carbon atoms.
Fatty acids are classified as saturated or unsaturated.

Contain no double bonds and are solid at room temperature.
Examples: Acetic acid (2C), Propionic acid (3C), Palmitic acid (16C), Stearic acid (18C).

Contain one (monounsaturated) or more double bonds (polyunsaturated) and are liquid at room temperature.
Polyunsaturated fatty acids (PUFAs) are essential fatty acids that cannot be synthesized in the human body.
PUFAs must be obtained from the diet.
PUFAs play a crucial role in growth and metabolism, act as anti-atherosclerotic agents, and are involved in the synthesis of hormone-like eicosanoids.
PUFAs are essential for skin integrity, reproduction, and blood clotting.
PUFAs contribute to the structure of cell membranes, prevent fatty liver, and are involved in the health of the retina.
PUFAs can also be oxidized for energy production.

Glycerol is a tri-hydric alcohol that is the alcohol present in neutral fat.
Sphingosine is the alcohol present in sphingolipids and glycolipids.
Cholesterol is a significant sterol in animal tissues and is a precursor for steroid hormones, bile salts, and vitamin D.
Cetyl and mericyl alcohols are present in waxes.

Simple lipids are esters of fatty acids with an alcohol.
Simple lipids are neutral lipids (uncharged) and are classified based on the alcohol involved:
- Neutral fats, which are esters of fatty acids with glycerol.
- Waxes, which are esters of fatty acids with long-chain alcohols other than glycerol.

Fats are solid at room temperature and are made up of glycerol and saturated fatty acids.
Oils are liquid at room temperature and are made up of glycerol and unsaturated fatty acids.

Rancidity is a chemical change in the properties of lipids caused by oxidation or hydrolysis.
Hydrolytic rancidity occurs when fats are hydrolyzed by lipases, leading to the release of glycerol and short-chain fatty acids with bad odor.
Oxidative rancidity is caused by the oxidation of fat by oxygen, light, or heat, resulting in peroxides, aldehydes, ketones, and other toxic compounds with bad odor.
Ketonic rancidity is due to fungal contamination, leading to the production of ketones with bad odor.

Compound lipids contain fatty acids, alcohols, and other groups.
Compound lipids are further classified as:
- Phospholipids
- Glycolipids
- Lipoproteins

Phospholipids contain fatty acids, alcohols, phosphoric acid, and often a nitrogenous base.
Phospholipids are categorized based on the alcohol they contain:
- Glycerophospholipids contain glycerol as the alcohol.
- Sphingophospholipids contain sphingosine as the alcohol.

Key components of cell membranes, regulating permeability.
Form the structural foundation of subcellular organelles, including endoplasmic reticulum, Golgi apparatus, mitochondria, the nucleus, and lysosomes.
Crucial components of the lipoprotein coat, aiding in lipid transport and preventing fatty liver.
Present in high amounts in the myelin sheath of nerves.
Involved in blood clotting and platelet aggregation (cephalin).
Dipalmitoyl lecithin, a major component of lung surfactant, is essential for proper lung function in newborns.

Lack of lung surfactant in newborns can lead to respiratory distress syndrome, which can be fatal.
Phospholipids are involved in signal transduction across the cell membrane (second messenger).
Phosphatidyl inositol plays an essential role in signal transduction.
Phospholipids provide polyunsaturated fatty acids that are necessary for the synthesis of eicosanoids.

Glycolipids contain carbohydrate residues, sphingosine, a long-chain fatty acid (24 carbon series), and they are present in cerebral tissue.
Glycolipids are also known as sphingogalactolipids or galactosides.
Glycolipids are classified according to the number and nature of the carbohydrate residues present.

Cerebrosides have one galactose molecule (galactoside), one glucose (glucoside), or one lactose (lactoside) and ceramide.
Sulfatides are cerebrosides with sulfate on the sugar (sulfated cerebrosides) and ceramide.
Gangliosides have multiple sugar and amino sugar residues, ceramide, and sialic acid.

Lipoproteins are spherical macromolecular complexes composed of lipids and specific proteins called apo-proteins.
Lipoproteins keep water-insoluble lipids in solution in aqueous plasma.
Lipoproteins provide a mechanism for transporting lipids to and from tissues.

Chylomicrons: 98- 99% fat and 1-2% protein. Transport dietary triglyceride from the intestine to peripheral tissues.
Very Low-Density lipoproteins (VLDL) or pre-β-lipoproteins: 90- 93% lipid and 7-10% protein. Transport endogenously synthesized TAG to extra-hepatic tissues.
Low-Density Lipoproteins (LDL) or β-lipoproteins: contain 10-20% protein (apolipoprotein B) and 80-90% lipids. Carry cholesterol to various tissues. Increased LDL levels in blood are linked to increased risk of atherosclerosis.
High-Density Lipoproteins (HDL) or α-Lipoproteins: 40% protein (apolipoprotein A) and 60% lipids. Act as cholesterol scavengers, transporting cholesterol from peripheral tissues to the liver for elimination. Increased HDL levels in blood are linked to decreased risk of atherosclerosis.
Albumin-Free Fatty Acid Complex: 99% protein and 1% long-chain free fatty acids. Transport free fatty acids.