Lipids Flashcards
Lipids
large,complex organic macromolecules (not polymers) that contain carbon, hydrogen, and oxygen
* Insoluable in water
* Triglycerides
* Phospholipids
Roles of lipids
- Soure of energy
- Waterproofing (insoluble in water e.g waxy cuticle)
- Insulation (help retain heat e.g polar bear fat)
- Protection (fat stored around kidney)
Triglycerides
- Function: -good source of energy, found in oil + butter
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Structure: 3 fatty acids and one glycerol molecule, Glycerol= fixed structure, organic alcohol (-OH)
Fatty acid= made of C, H and some O (-COOH), have different R-groups that give lipids different properties, hydrophobic - Triglycerides are non-polar, so it doesnt mix with water (immisscible)
Ester Bond
- Formed in a condensation reaction between 3 fatty acids and glycerol
- The bond between a fatty acid and glycerol atom is the ester bond
- Water is formed as a result (1 oxygen atom and 2 hydrogen atoms removed in the process)
- Covalent bond
- Also known as an ‘esterification’
- Triglycerides have 3 ester bonds
- Hydrolysis reverts triglyeceride back into 3 fatty acids and glycerol
Fatty acid R-groups:
- Saturated
- Mono-unsaturated
- Polyunsaturated
Saturated
No carbon-carbon double bonds
* all the carbon atoms are linked to maximum number of hydrogen atoms
* Found mostly in animals and fluids
Monosaturated
One (single) double bond between carbon atoms
Polyunsaturated
more than one double bond between carbon atoms
* Double bonds cause molecule to bond
* They are less compact so they are liquids at room temperature (oils)
Structure of triglycerides related to its properties:
- High ratio of carbon-hydrogen bonds to carbon atoms = excellent source of energy
- Low mass to energy ratio = good storage molecules as much energy can be stored in a small volume (compact)
- Large non-polar molecules = insoluble in water so doesnt affect osmosis in cells
- High ratio of H to O atoms = release water when oxidised so provide an important source of water (for organisms in dry deserts)
Phospholipids
2 fatty acids, a glycerol and a phosphate molecule
* Used in cell membranes (phospholipid bi-layer) to control cell contents that pass through
* Hydrophobic fatty acid tail- NON-POLAR, orients(repels) itself away from water but mixes readily with fat
* Hydrophillic phosphate head- interacts with water (attracted to it) but not fat
Phosphate ester bond
formed during a condenstation reaction between fatty acids and phosphate……
Structure of phospholipids related to properties:
- Polar molecules (hydrophylic head and hydrophoic tails) - in an aqueous solution a bi-layer is formed within cell-surface membranes
- Hydrophillic phosphate heads- help to hold at the surface of the membrane
- Glycolipids- Structure allows these to be formed by combining carbohydrates within the membrane
Phospholipids in water
- Hydrogen ions disociate from from the phosphoric acid
- A phosphate group with a negative charge is formed = hydrophilic head which is attracted to water
- Fatty acid tails are non-polar (no charge) so they repel water
- Hydrophillic head faces towards the water
- Hydrophobic tail faces outwards, away from water
Lipids
Use a dry/grease free test tube:
1. Dissolve the sample in ethanol
2. Add distilled water + shake
3. Positive test= white emulsion forms (liquid turns from clear to cloudy white)
