2.2.7 Lipids & Ester Bonds

Question 1

Lipids

Answer 1

Lipids a re macromolecules that contain carbon, hydrogen and oxygen atoms
Unlike carbohydrates, lipids contain a lower proportion of oxygen
Lipids are non-polar and hydrophobic (insoluble in water)
There are two groups of lipids that are you will need to know:
- triglycerides (the main component of fats and oils)
- phospholipids
Lipids play an important role in energy yield, energy storage, insulation and hormonal control

Question 2

Triglycerides

Answer 2

Triglycerides are non-polar, hydrophobic molecules
The monomers that make up triglycerides are glycerol and fatty acids
Glycerol is an alcohol (an organic molecule that contains a hydroxyl group bonded to a carbon atom)
Fratty acids contain a methyl group at one end and of a hydrocarbon chain, known as the R group (chains of hydrogens bonded to carbon atoms, typically 4-24 carbons long) and at the other end is a carboxyl group
- the shorthand chemical formula for a fatty acid is RCOOH
Fatty acids can vary in two ways:
- length of the hydrocarbon chain (R group)
- the fatty acids chain (R group) may be saturated (mainly in animal fat) or unsaturated (mainly in vegetable oils, although they’re are exceptions e.g. coconut and palm oil)
Unsaturated fatty acids can be mono or poly-saturated
- if H atoms are on the same side of the double bond, they are cis-fatty acids and are metabolised by enzymes
- if H atoms are on the opposite side of the double bonds, they are trans-fatty acids and cannot from enzyme-substrate complexes, and therefore are not metabolised
- trans-fat is linked to coronary heart disease

Question 3

Phospholipids

Answer 3

Phospholipids are a type of lipid, therefore they are formed from the monomers glycerol and fatty acids
Unlike triglycerides, there are only 2 fatty acids bonded to a glycerol molecule in a phospholipid, as one has been replaced by a phosphate ion (PO4 3-)
As the phosphate is polar, it is soluble in water (hydrophilic)
The fatty acid ‘tails are non-polar and therefore insoluble in water (hydrophobic)
Phospholipids are amphipathic (they have both hydrophobic and hydrophilic parts)
As a result of having hydrophobic and hydrophilic parts, phospholipids molecules form mono layers or bilayers in water

Question 4

Phospholipids vs Triglycerides

Answer 4

No. Of Fatty Acid Tails
- P = 2
- T = 3
Presence of Phosphate
- P = yes
- T = no
Polar/Non-Polar
- P = polar phosphate head
- T = non-polar
No. Of Water Molecules Released During Formation
- P = 3
- T = 3
Function
- P = cell membrane components
- T = energy storage

Question 5

The Ester Bond

Answer 5

Triglycerides are formed by esterification
An ester bond forms when a hydroxyl (-OH) group from the glycerol bonds with the carboxyl (-COOH) group of the fatty acid
- an H from the glycerol combines with an OH from the fatty acid to make water
- the formation of an ester bond is a condensation reaction
- for each ester bond formed, a water molecule is released
- 3 fratty acids join 1 glycerol molecule to form a triglyceride
- therefore for 1 triglyceride to form, 3 water molecules are released