Lipids: Triglycerides | A-level Biology | OCR, AQA, Edexcel

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They key points covered in this video include:

1. Introduction to Lipids
2. Structure of Triglycerides
3. Ester Bonding - Condensation
4. Ester Bonding - Hydrolysis

Introduction to Lipids

Lipids are organic molecules with two main types - triglycerides and phospholipids. Triglycerides and phospholipids have different but important roles:Triglycerides are a good source of energy, Phospholipids have a structural role in cell membranes. Lipids are mostly composed of carbon and hydrogen with some oxygen. Lipids are large, complex molecules (macromolecules) but they are not polymers. Lipids are also non-polar molecules and therefore they will not dissolve in water.

Structure of Triglycerides

A triglyceride molecule is formed from one molecule of glycerol and three fatty acids. Glycerol is an organic alcohol which has three hydroxyl (-OH) groups. Fatty acids are organic acids that have a carboxyl (-COOH) group joined to a hydrocarbon tail - they are a type of carboxylic acid. The letter R is often used to represent the hydrocarbon chain.

Ester Bonding - Condensation

A triglyceride molecule is formed by joining one molecule of glycerol to three fatty acids through condensation reactions. A condensation reaction forms water as one oxygen atom and two hydrogen atoms are removed from the glycerol and fatty acid. The bond formed between the glycerol and the fatty acid is called an ester bond. An ester bond is the covalent bond formed by a condensation reaction between the -OH group of a carboxylic acid and the -OH group of an alcohol. Three condensation reactions are needed to make a triglyceride, forming three molecules of water. Triglycerides therefore contain three ester bonds.

Ester Bonding - Hydrolysis

Triglycerides can be broken down into glycerol and three fatty acids in three hydrolysis reactions.This requires three molecules of water as three oxygen atoms and six hydrogen atoms are added to the triglyceride. This breaks the three ester bonds, forming glycerol and three fatty acids.

Summary

Lipids are organic molecules composed of carbon, hydrogen and oxygen
Lipids are macromolecules but not polymers
Triglycerides are lipids that are formed by condensation reactions between glycerol and three fatty acids
Triglycerides are broken down into glycerol and three fatty acids in hydrolysis reactions
The three condensation reactions form three molecules of water and the three hydrolysis reactions require three molecules of water
The three bonds formed in a triglyceride are called ester bonds

Видео Lipids: Triglycerides | A-level Biology | OCR, AQA, Edexcel канала SnapRevise