In This A-Level Biology Lesson “Lipids: The Properties of Triglycerides” the learning outcomes lay out the key points covered in the lesson as usual. Then we discuss how the structure of triglycerides are related to their functions - a quick re-emphasis of the point that lipids are not polymers and we move on to the fact that lipids are hydrophobic molecules. The lesson progresses with and outline of why lipids are useful energy storage molecules, lipids are waterproofing agents, lipids are great insulators and protectors and lipids play important roles as steroids. When you’re super confident that you can relate the structure and function of triglycerides to their many functions in nature then you’re ready to have a go at the knowledge check questions. As always, you’ll be able to check your answers with mine written in the back of the work book and see exactly how you should write your answers in a way that gains maximum marks in the exams!

A-Level Biology "Lipids: The Properties of Triglycerides"

The structure of triglycerides is related to their functions. For example, the long hydrocarbon tail of the fatty acid part of “fats” is an important source of energy. In fact, fatty acids contain around twice as much energy per gram than do carbohydrates.

Remember! Lipids are NOT considered Polymers (Why? Because they are NOT composed of many repeating monomers).

Lipids are made up from: - Glycerol + Fatty acids.

Fats and oils are insoluble in water, and this hydrophobic nature of lipids allows them to “bundle” together forming fat droplets. It is also yet another reason fat is a great energy storage molecule, since they don’t affect the water potential of cells.

The hydrophobic properties of lipids make them useful waterproofing agents, e.g. bird feathers, leaves the waxy exoskeletons of many insects.

Fats have a low density which makes them useful for buoyancy, insulation and protection.

Lipids play important roles as steroids (e.g. Cholesterol).

Lipids are useful respiratory substrates. During Cellular Respiration, lipids are oxidised and the bonds of the hydrocarbon tail are hydrolysed – the products of which enter the ‘link reaction’ to produce ATP.