Lipids (3.1.3) Flashcards
What are the elements present in lipids?
- Carbon
- Hydrogen
- Oxygen
Compared to carbohydrates how does the proportion of hydrogen and oxygen compare in lipids
- Lipids have a higher proportion of hydrogen and a lower proportion of oxygen
What are lipids made up of?
- Fatty acids
- Glycerol
What are the properties of lipids?
- Insoluble in water
- Soluble in organic solvents, e.g. alcohol
- Can be either solid (fat) or liquid (oil) at room temperature
What is the general formula of fatty acids?
- R-COOH
What do the parts of the general formula of fatty acids represent?
- The R represents a long hydrocarbon chain
- The COOH represents the carboxylic acid group
What does saturated and unsaturated mean?
- Saturated meaning no double bonds between the carbon atoms
- Unsaturated meaning one or more double bonds between the carbon atoms
What happens in a condensation reaction between a glycerol and a fatty acid?
- An ester bond is formed
How can lipids be hydrolysed into fatty acids and glycerol?
- Heating with an acid or an alkali
- Use of the enzyme lipase at its optimum temperature
What does hydrophilic and hydrophobic mean?
- Hydrophilic means attracting water
- Hydrophobic means repelling water
What are triglycerides?
- Hydrophobic lipids that act mainly as energy stores in plants and animals
- They are composed of one glycerol molecule and three fatty acids
- Formed through three separate condensation reactions and the removal of three molecules of water
What is the word equation for the formation of a triglyceride?
- glycerol + 3 fatty acids → triglyceride + 3 water
What are the properties and roles of triglycerides?
- Many carbon-hydrogen bonds → so releasing twice the energy of carbohydrates during aerobic respiration
- High hydrogen to oxygen ratio → so releases water during aerobic respiration, vital for desert organisms
- Non-polar and insoluble in water → so osmotically inactive, making them ideal for energy storage
- Found in waxy cuticle → so reduces water loss in insects and plant leaves
What are phospholipids?
- Lipids containing a phosphate group
- They are composed of one glycerol molecule, two fatty acids and one phosphate group
What is unique about phospholipids?
- They have a hydrophilic head continuing the phosphate group
- They have a hydrophobic tail consisting of the long fatty acid chains
What are the similarities (compare) between triglycerides and phospholipids?
- Insoluble in water
- Contains glycerol
- Contains carbon, hydrogen and oxygen
- Contains ester bonds
What are the differences (contrast) between triglycerides and phospholipids?
- Triglycerides have 3 fatty acids but phospholipids have 2 fatty acids and a phosphate group
- Triglycerides are hydrophobic but phospholipids have hydrophilic and hydrophobic regions
- Phospholipids form a bilayer in water but triglycerides do not
Describe the emulsion test and positive result for lipids
- Add ethanol
- Shake the mixture
- Add water to the mixture
- A white emulsion indicates lipid is present
