Lipids Overview

Overview of Lipids

• Lipids are essential biomolecules categorized into four families: fats, phospholipids, steroids, and waxes.
• Primary functions include energy storage and membrane construction in organisms.

Polarity of Lipids

• Composed of hydrophobic molecules primarily containing carbon, hydrogen, and oxygen.
• Exhibit fewer polar O-H bonds and a higher number of non-polar C-H bonds, leading to low solubility in water.
• Soluble in non-polar solvents and can contain long hydrocarbon chains or compact ring structures.

Energy Storage

• Lipids serve as the dominant energy-storing molecules in living organisms.
• Contain approximately 38 kJ of chemical energy per gram, exceeding the energy stored in carbohydrates or proteins (around 17 kJ).

Conversion of Excess Carbohydrates

• Excess carbohydrates in the body are converted into fat for storage.
• Fat molecules accumulate as droplets in adipose tissue, providing insulation and a protective layer under the skin.

Triglycerides (Triacylglycerols)

• Most prevalent type of fat, comprising glycerol (a 3-carbon alcohol) and three fatty acids.
• Fatty acids contain long hydrocarbon chains (16-18 carbons long) with a carboxyl group at one end.

Esterification Process

• Formation of triglycerides occurs through esterification, a condensation reaction creating ester bonds between glycerol and fatty acids.
• Water is produced by removing a hydrogen from glycerol and a hydroxide from the fatty acid during the process.

Fat Types

• Saturated Fat: Solid at room temperature, consists of single bonds, and causes kinks in the chain.
• Unsaturated Fat: Contains at least one double bond, remains liquid at room temperature, and has fewer hydrogens attached.

Health Implications of Saturated Fats

• Longer hydrocarbon chains increase London dispersion forces, resulting in decreased solubility and increased difficulty in breakdown.
• Consumption of saturated fats is linked to increased risks of heart disease.

Trans-Fat

• Man-made unsaturated fat characterized by trans-based double bonds, resulting in straight fatty acid chains and reduced solubility.
• Our bodies struggle to break down these bonds, posing health risks.

Phospholipids

• Phospholipids form the primary component of cell membranes.
• Composed of glycerol, two non-polar fatty acids, and one phosphate group. The phosphate is charged and generally connects to a polar molecule.

Phospholipid Structure

• Amphipathic nature: phosphate group is polar (hydrophilic) while fatty chains are non-polar (hydrophobic).
• Arranges in a micelle formation with tails facing inward and heads facing outward, protecting the tails from water.

Phospholipid Bilayer

• Cell membranes consist of a phospholipid bilayer with fatty chains inside and phosphate heads outside, controlling substance entry/exit.
• Water and polar molecules typically require assistance to penetrate the layer.

Steroids

• Steroids possess a structure of four fused carbon rings, with unique groups attached defining each steroid.
• Common steroids include sterols, generally hydrophobic with one hydroxyl group (slightly polar). Examples: testosterone and cholesterol.

Sterols and Health Effects

• Cholesterol: High levels can cause atherosclerosis, obstructing arteries and increasing heart attack risks.
• Testosterone: Regulates sex traits and gamete development; anabolic steroids can raise blood pressure and impair growth.

Waxes

• Waxes comprise long fatty acid chains attached to alcohols or carbon rings, classified as hydrophobic and non-polar soft solids.
• Cutin, a wax found on plants, offers waterproofing, aiding in water conservation and infection protection.