Lipids

What are the two main lipids?

Triglycerides and Phospholipids

What are triglycerides

Formed by a condensation reaction between one molecule of glycerol and three molecules of fatty acid.

What two groups do the condensation reactions occur between to form ester bonds?

Hydroxyl groups of glycerol and the carboxyl group of the fatty acids.

What is the R group in fatty acids?

The variable hydrocarbon group, attached to a carboxyl group.

Saturated vs unsaturated fatty acids

Saturated: Contain no C=C double bonds. Unsaturated: Contain at least one C=C double bond.

How do the double bonds affect the properties of fatty acids?

Saturated fatty acids are usually solid at room temp as their straight shape allows them to pack closely together. Unsaturated fatty acids are usually liquid at room temp as their kinks mean they cannot pack tightly together, lowering their melting point.

What are phospholipids

Glyceride, two fatty acids and a phosphate group. They are polar and the phosphate head is hydrophilic, while the fatty acid tail is hydrophobic. Two ester bonds and one phosphoester bond.

What is a phospholipid bilayer?

Phospholipids spontaneously self-assemble to a bilayer in aqueous environments. Heads point outward toward the cytoplasm and extracellular fluid. Tails sandwich together on the inside, blocking water-soluble substances.

How does the structure of a triglyceride aid its function

The high ratio of energy storing C-H bonds to carbon atoms = efficient energy storage. Large non-polar and insoluble means they do not alter the water potential of the cell. High ratio of hydrogen to oxygen atoms: release metabolic water when oxidised.

How does the structure of a phospholipid aid its function?

Form bilayer as in an aqueous environment, hydrophilic heads face outward toward water, while hydrophobic tails point inward away from water. Kinks in unsaturated fatty acid tails prevent packed rigidity increasing fluidity and flexibility Combine with carbohydrates at the cell-surface membrane to create glycolipids, which are crucial for cell recognition

Describe the emulsion test for lipids.

1. Add ethanol to the test sample 2. Shake thoroughly to dissolve any lipid present 3. Add distilled water to the mixture and shake gently. 4. A cloudy white emulsion should form