Lipids Flashcards
Describe the properties of lipids
- insoluble in water
- soluble in other solvents like ethanol and other lipids
- contain C, H, O
What are the two types of lipids?
- Phospholipids
- Triglycerides
What are the functions of triglycerides?
- buoyancy
- storage of energy
- thermal insulation/electrical insulation
- shock absorption
Why are triglycerides buoyant?
- Many single celled organisms produce oil drops to aid buoyancy
Why are triglycerides good for energy storage?
- Energy store in seeds
- Energy store animals
- Lipids yield twice as much energy per gram than carbohydrate
Why do triglycerides aid in thermal and electrical insulation?
- adipose tissue eg. In neurones
Why do triglycerides aid in shock absorption?
- organs such as kidneys have fat around them for protection against knocks and any impact
Describe the structure of a triglyceride molecule
- one molecule of glycerol and three molecules of fatty acid tails bonded by three ester bonds by condensation reaction
What are fatty acid tails composed of?
- 15- 17 hydrocarbons in which the R group can be saturated or unsaturated with an acid group at the end of
Describe the difference between a triglyceride and phospholipid
- triglycerides contain three fatty acid tails whereas phospholipids contain two fatty acid tails because one of them is substituted by a phosphate group
What are the similarities between triglycerides and phospholipids?
- Both triglycerides and phospholipids are bonded with glycerol and fatty acids to make ester bonds through condensation reaction
Properties of Saturated Fatty Acids
- Contain only single C–C bonds • Closely packed
- High melting points
- Solids at room temperature
- Animal fats
- More Hydrogen’s than unsaturated
- Straight tail
Properties of Unsaturated Fatty Acids
- Contain one or more double C=C bonds
- Nonlinear chains do not allow molecules to pack closely
- Low melting points
- Liquids at room temperature
- Plant oils
- Less hydrogen’s than saturated fats
- Kink/bend in tail
Why are fatty acids with double bonds liquids?
- double bonds kink the hydrocarbon chain preventing the chains from packing together
- lowers melting temperature
Why are fatty acids with no double bonds solids?
- hydrocarbon chains pack together to make a solid fat
What is glycerol?
- three carbon carbohydrate
- contains three alcohol groups (-OH) which link up with acid tours in the fatty acids
Describe the test for lipids
- emulsion test
- place food sample in test tube (if solid, should be ground up first using pestle and mortar)
- dissolve sample in ethanol to test and shake
- fill up another test tube with cold water
- pour previous test tube with food sample and ethanol into test tube with water and shake
- if lipid is present should form a white emulsion
Draw the structure of glycerol
Draw the structure of fatty acids
Draw the structure of triglyceride
What are saturated fatty acids?
- hydrocarbon chain has only single bonds between carbons
What are unsaturated fatty acids?
- hydrocarbon chain consists of at least one double bond between carbons
What are the properties of triglycerides?
- energy storage
- metabolic water source
- insoluble in water
- relatively low mass
Why are triglycerides good for energy storage?
- due to large ratio of energy storing carbon-hydrogen bonds compared to the number of carbon atoms, a lot of energy is stored in the molecule
Why are triglycerides a metabolic water source?
- due to high ratio of hydrogen to oxygen atoms they act as metabolic water source
- can release water if they are oxidised which is essential for animals in the desert such as camels
What is the advantage of lipids having a relatively low mass?
- a lot can be stored without increasing the mass and preventing movement
What are the properties of phospholipids?
- hydrophilic head
- phosphate is charged
- fatty acid chain is not charged
- fatty acid chain is hydrophobic
What does it mean if phospholipid head is hydrophilic and charged?
- can attract with water as it is charged
What does it mean if phosphate is charged?
- repels other fats
What does it mean if the fatty acid chains are hydrophobic?
- repels water but will mix with fats
Describe the structure of a phospholipid bilayer
- in water they are positioned so that the heads are exposed to water and the tails are not, forming a phospholipid bilayer
- have two charged regions (heads) so are polar
Draw the structure of phospholipid
