Lipids

Question 1

Describe the test to show the presence of lipids

Answer 1

• add sample to a test tube
• add ethanol to sample + shake test tube then add water
• white/milky emulsion = positive test
• greater conc of lipid = whiter, easier to distinguish emulsion

Question 2

What are the functions of triglycerides?

Answer 2

• energy storage: long hydrocarbon chains containing many C-H bonds that release lots of energy when broken + have a low mass:energy ratio
• insoluble: don’t affect water potential bc are large + hydrophobic
• insulation: fats are slow conductors of heat so retain body heat beneath body surface
• protection: some form protective, waterproof layers on external surface of organisms
• act as a metabolic water source due to high ratio of H to O atoms

Question 3

What are the functions of phospholipids?

Answer 3

• makes up phospholipid bilayer of cell membranes: centre is hydrophobic so difficult for water-soluble substances to pass through it
• composition affects fluidity of cell membrane based on saturated/unsaturated bonds
• controls membrane protein orientation

Question 4

What are the properties of phospholipids?

Answer 4

• have a water soluble hydrophilic head + a water repelling hydrophobic tail
• phosphoester bond between phosphate + glycerol + an ester bond between glycerol + each fatty acid

Question 5

What are the differences between triglycerides (T) + phospholipids (P)?

Answer 5

• T have 3 fatty acids whereas P have 2 fatty acids
• P contain a phosphate group whereas T don’t
• P have a phosphoester bond + 2 ester bonds whereas a T has no phosphoester bonds + 3 ester bonds