DNA, Starch & Proteins
Specification Point 9.25C:
a) DNA is a polymer made from four different monomers called nucleotides (names of nucleotides not required)
b) starch is a polymer based on sugars
c) proteins are polymers based on amino acids
- DNA consists of four different monomers called nucleotides abbreviated to A, T, C, and G which are bound together by polymerisation.
- The nucleotides form two strands that intertwine, giving the famous double helix shape of DNA.
- It is a complex molecule that contains genetic information.
Diagram showing the complex double helix structure of DNA
- Carbohydrates are compounds of carbon, hydrogen and oxygen with the general formula Cx(H2O)y.
- There are simple carbohydrates and complex carbohydrates.
- Simple carbohydrates are called monosaccharides and are sugars such as fructose and glucose.
- Complex carbohydrates are called polysaccharides such as starch and cellulose.
- Complex carbohydrates are condensation polymers formed from simple sugar monomers and, unlike proteins, are usually made up of the same monomers.
- A H2O molecule is eliminated when simple sugars polymerise. The linkage formed is an -O- linkage called a glycosidic linkage.
Diagram of the starch Amylose showing glycosidic linkages (-O-) which bind the monomers together
- Proteins are condensation polymers which are formed from amino acid monomers joined together by peptide bonds.
- Amino acids are small molecules containing amine (-NH2) and carboxylic acid (-COOH) functional groups.
- A peptide link is formed when a carboxylic acid and an amine react:
R-COOH + R-NH2 → R-C=ONH-R + H2O
(R represents a hydrocarbon side chain)
- Most proteins contain at least 20 different amino acids.
- These are the monomers which polymerise to form the protein.
Diagram showing condensation polymerisation in which a protein is formed
Edexcel GCSE Chemistry Notes
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