1.4 Flashcards
What are lipids? And what characteristics do they have?
Lipids are a large group of molecules that share similar characteristics:
1- They contain carbon, hydrogen and oxygen
2- The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates
3- They are insoluble in water
4- They are soluble in organic solvents eg. alcohol and acetone
What are the three main groups of lipids?
The three main groups of lipids are:
1. Triglycerides (fats and oils)
2. Phospholipids
3. Waxes
Main role of lipids? How do phospholipids contribute?
The main role of lipids is in plasma membranes. Phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them.
4 other roles of lipids?
1)an energy source. When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate.
2)waterproofing. Lipids are insoluble in water and are therefore useful as a waterproofing material. Both plants and insects have waxy cuticles that conserve water, whilst mammals produce an oily secretion from the sebaceous glands in the skin.
3)insulation. Fats are slow conductors of heat and when stored beneath the body surface help to retain body heat.
4)protection. Fat is often stored around delicate organs, such as the kidney.
How are triglycerides formed?
Triglycerides are formed from the condensation reaction of three fatty acids with a molecule of glycerol.
How can the condensation reaction be reversed? What is the name of the bond reversed?
This can be reversed by a hydrolysis reaction (addition of water) The bond formed is called an ester bond (a type of covalent bond).
Saturated?
No carbon-carbon double bond
Mono-unsaturated?
One carbon-carbon double bond
Poly unsaturated?
More than one carbon-carbon double bond
What are phospholipids made of?
Each phospholipid is made of a 3-carbon compound called glycerol:
• Two of the glycerol carbons are attached to fatty acids. This is hydrophobic/non-polar tail
• The third glycerol carbon is attached to an organic molecule, that also includes a bond to a
phosphate group. This is hydrophilic/polar head
Test for lipids?
1)Take a completely dry and grease-free test tube.
2)To 2cm^3of the sample being tested, add 5 cm^3 of ethanol.
3)Shake the tube thoroughly to dissolve any lipid in the sample.
4)Add 5cm^3 of water and shake gently.
5) A cloudy, white solution indicates the presence of a lipid.
6) As a control, repeat the procedures using water instead of the sample; the final solution should remain clear.
What is hydrophobic?
When molecules repel water
What is hydrophilic?
When molecules attract water
