21 WJEC Biology AS Level - Marianne Izen - 2nd Edition Flashcards
Ester bond
An oxygen atom joining two atoms, one of which is a carbon atom attached by a double bond ond to another oxygen atom.
Describe the features of chitin
Chitin is a structural polysaccharide
It is found in the exoskeleton of insects and in fungal cell walls.
It resembles cellulose, with its long chains of B-1,4-linked monomers, but has groups derived from amino acids added, to form a heteropolysaccharide.
It is strong, waterproof and lightweight.
Like cellulose, the monomers are rotated through 180° in relation to their neighbours, and the long parallel chains are cross-linked to each other by hydrogen bonds, forming microfibrils.
Describe the formation of triglycerides
Triglycerides are formed by the combination of one glycerol molecule and three molecules of fatty acids.
The glycerol molecule in a lipid is always the same but the fatty acid component varies.
The fatty acids join to glycerol by condensation reactions, whereby three molecules of water are removed and ester bonds are formed between the glycerol and fatty acids.
cell wall
beta
glycosidic
180
hydrogen
microfibrils
Describe the basic features of lipids
Like carbohydrates, lipids contain carbon, hydrogen and oxygen but, in proportion to the carbon and hydrogen, they contain much less oxygen.
They are non-polar compounds and so are insoluble in water, but dissolve in organic solvents, such as propanone and alcohols.
