Biological Molecules: - Lipids

- Lipids - 

- The Role Of Lipids - 

S ● W ● I ● P 

This helped me remembering the roles of lipids -

S ⇒ Source of energy 

lipids provide twice the energy as carbohydrates at the same mass when hydrolysed

W ⇒ Waterproofing 

Lipids are insoluble in water // plants and insects have a waxy cuticle reducing water loss whereas mammals have an oily secretion from sebaceous gland in the skin. 

I ⇒ Insulation 

Fats = slow conductor of heat // stored beneath the body surface to help retain heat 

P ⇒ Protection 

Fat stored around delicate organs i.e. Kidneys.

There are 2 types of lipids 

Phospholipids and Triglyceride 

So what is the difference?

Phospholipids have two parts

To remember there are two parts 

PHOSPHOLIPIDS = PHO is repeated twice within the word - therefore two parts :) 

Triglycerides have 3 fatty acids. 

To remember there are 3 fatty acids.

TRIGLYCERIDE = TRI means 3 

- Phospholipids -

- The two parts of the phospholipids is:

⇒ Hydrophilic 'head' = interacts with water (attracted to) // does not readily mix with fat. 

⇒ Hydrophobic 'tail' = orients itself away from water (repels against) // readily mixes with fat. 

- It has two ends and is said to be polar as they behave differently. 

- Structure of phospholipids 

⇒ Phospholipids are polar molecules - in aqueous environment phospholipid bilayer is formed hydrophobic barrier is formed between the cell (inside and outside).

⇒ Hyrdophilic 'head' helps hold at the surface of the cell-surface membrane.

⇒ Structure allows the formation of glycolipids // combining carbohydrates with the cell surface membrane. Acts as a cell recognition site.

- Triglycerides - 

3 fatty acids joined to a glycerol 

( TRI = 3 // GLYCERIDE = glycerol. )

The bond formed = ester bond (through condensation reaction) 

There are 70 different types fatty acids, all have a carboxyl ( -COOH ) group attached with a hydrocarbon chain. 

If this chain does not have carbon-carbon double bond = Saturated 

If this chain has a single double bond = Mono-UnSaturated 

If this chain has more than one double bond = Polyunsaturated

To remember the difference between unsaturated and saturated. 

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UN-SATURATED = There are two parts to the word which can imply double bond 

SATURATED = A single word which can imply a single bond. 

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Structure of triglycerides - 

⇒ High ratio of energy-storing carbon-hydrogen bonds to carbon atoms // excellent source of energy. 

⇒ Low mass to energy ratio // good storage molecule = so much energy can be stored in small volume. Reduced mass in animals so able to move around. 

⇒ Large, non polar & insoluble // storage does not effect osmosis in cells or the water potential 

⇒ High ratio of hydrogen to oxygen atoms // release water when oxidised provides an important source of water.