triglycerides and phospholipids

Overview

This lecture covers the structure, formation, properties, and testing methods of triglycerides and phospholipids, key lipid types in biology.

Triglycerides consist of one glycerol molecule bonded to three fatty acids.
Each fatty acid attaches via a condensation reaction, forming an ester bond and releasing a water molecule.
Three condensation reactions form a triglyceride, creating three ester bonds and releasing three water molecules.
Fatty acid chains are denoted as "R groups" because their length and saturation can vary.

Saturated fatty acids have only single bonds between carbon atoms; fully saturated with hydrogen.
Unsaturated fatty acids have at least one double bond between carbon atoms; fewer hydrogens.

Triglycerides serve as energy storage due to many carbon-hydrogen bonds storing large amounts of energy.
High hydrogen to oxygen ratio allows triglycerides to act as a metabolic water source when oxidized.
Triglycerides are hydrophobic and insoluble in water, preventing osmotic issues in cells.
Lipids are less dense than tissues like muscle, allowing energy storage without greatly increasing body mass.

Lipid detection involves dissolving the sample in ethanol, then adding distilled water and shaking.
A positive result is a white emulsion (not a precipitate), indicating presence of lipids.

Phospholipids have a glycerol, two fatty acids, and a phosphate group (replaces the third fatty acid).
Formed by two condensation reactions, creating two ester bonds.
The phosphate group is negatively charged, forming a hydrophilic (water-attracting) head.
Fatty acid tails are hydrophobic (water-repelling).
In water, phospholipids form a bilayer with tails inward and heads outward, forming cell membranes.
Phospholipids are polar due to distinct hydrophilic and hydrophobic regions.

Glycerol — a three-carbon alcohol serving as a backbone for triglycerides and phospholipids.
Fatty acid — hydrocarbon chain with a carboxylic acid group; can be saturated or unsaturated.
Ester bond — a chemical bond formed between glycerol and fatty acids during condensation.
Condensation reaction — a reaction where two molecules join, producing water as a byproduct.
Hydrophobic — repels water.
Hydrophilic — attracts water.
Phospholipid bilayer — double layer of phospholipids forming cell membranes.
Emulsion — mixture where lipids form tiny droplets in water, resulting in a milky appearance.

Learn and be able to draw the structure of triglycerides and phospholipids.
Memorize the steps and positive result for the emulsion test.
Understand and be able to explain the properties and biological functions of triglycerides and phospholipids.