S1-lipids Flashcards
(14 cards)
What characteristics do all lipids share?
- Contain carbon, hydrogen and oxygen
- They are insoluble in water
- Soluble in organic solvents
- Proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates
What are the roles of lipids and how do they do those roles?
- Cell membranes - Phospholipids make it more flexible, transfer lipid soluble substances
- Energy source - When oxidised provide over twice the amount of energy as the same mass of carbohydrate, release valuable water
- Waterproofing - Lipids-insoluble in water
- Insulation - slow conductors of heat, act as electrical insulators in myelin sheath around nerve cells
- Protection - stored around delicate
How are triglycerides formed?
- 3 fatty acids and glycerol
- Ester bonds
- Condensation reactions
What is the same in all triglycerides?
The glycerol molecule
How many different fatty acids are there and what are they made up of?
- Over 70
- A carboxyl(-COOH) group
- Hydrocarbon chain
What is a saturated fatty acid?
- There are no double bonds between carbons
* Carbon is linked to the maximum number of hydrogen
What are the types of unsaturated fatty acids and their properties?
- Mono-unsaturated - one double bond between carbon
- Poly-unsaturated - more than one double bond between carbons.
- Double bonds cause them to bend.
- So cant pack together as closely and saturated.
- Therefore they are liquid at room temperature
How is the structure of triglycerides related to their properties?
- High energy-storing carbon-hydrogen bonds to carbon atoms ratio - so good source of energy.
- Low mass to energy ratio - so good storage molecule as a lot of energy can be stored in a small area.
- Large and non-polar - insoluble in water - doesn’t effect osmosis or water potential.
- High ration of hydrogen to oxygen so release water when oxidised - important source of water
How are phospholipids similar and different to lipids?
- Similar structure but have 2 fatty acids and glycerol
* One fatty acid is replaced with a phosphate group
Describe the structure of a phospholipid
- Made of 2 fatty acids, glycerol and a phosphate group
- Phosphate ‘head’ which is hydrophilic
- Hydrocarbon ‘tail’ which is hydrophobic
What are described as polar?
a molecule which has 2 ends with opposite charges
How is the structure of phospholipids related to their function?
- Polar molecules- hydrophilic head, hydrophobic tail- in aqueous environments form bilayer in cell-surface membrane- hydrophobic barrier between inside and outside of cell.
- Hydrophilic head help hold at surface of the cell surface membrane.
- Structure allows carbohydrates in cell-surface membrane to combine-forming glycolipids- important in cell recognition
What is the test for lipids?
EMULSION TEST
- Take completely dry, grease-free test tube.
- And 5cm^3 ethanol to 2cm^3 sample
- Shake test tube
- Add 5cm^3 water
- Shake test tube
Positive test = cloudy white
Why does the positive test for lipids occur?
- Lipid is finely dispersed in the water - forms emulsion.
- Light passing through is refracted as it passes from oil droplets to water droplets.
- Making it appear cloudy.
