Formula sheet: Biomolecules
Biomolecules12 min readLesson 1 of 5
1.1 Carbohydrates at a glance
A carbohydrate is a polyhydroxy aldehyde or ketone, or a compound that gives one on hydrolysis. Carbohydrates are grouped into:
| Group | Members | Behaviour |
|---|---|---|
| Monosaccharide | Glucose, fructose, ribose | Cannot be hydrolysed to a smaller sugar |
| Disaccharide | Sucrose, maltose, lactose | Two monosaccharide units joined through a glycosidic linkage |
| Polysaccharide | Starch, cellulose, glycogen | Many monosaccharide units |
Sugars that reduce Tollens or Fehling reagent are reducing sugars; sucrose is the usual non reducing example. Glucose and fructose are both C6H12O6, but glucose is an aldohexose and fructose is a ketohexose. Glucose has one aldehyde carbon, five hydroxy carbons and three chiral centres, so it has 2 to the power 3, that is eight, stereoisomers in principle.
1.2 Identifying tests
| Reagent | What it shows |
|---|---|
| Tollens reagent | Aldehyde group, silver mirror |
| Fehling solution | Reducing sugar, red precipitate |
| Bromine water | Glucose is oxidised to gluconic acid, fructose is not |
| Nitric acid | Glucose gives saccharic acid, shows both ends |
| Acetic anhydride | Penta-acetate from glucose, showing five OH groups |
| Methyl iodide with Ag2O | Methylation of the hydroxyl groups |
| HCN | Cyanohydrin, confirms the aldehyde group |
| Phenylhydrazine | Osazone, confirms the sugar |
1.3 Protein and enzyme facts
Amino acids join by peptide bonds, and the sequence of amino acids is the primary structure. The regular local shapes, alpha helix and beta pleated sheet, are the secondary structure; the overall three dimensional fold is the tertiary structure; and the assembly of subunits is quaternary.
Enzymes are proteins that catalyse reactions of living systems. They are specific for both the reaction and the substrate, and they are efficient, working under mild conditions of temperature and pH. An enzyme contains an active site; the substrate fits into it like a key in a lock, or by the induced fit model where the site adjusts to the substrate.
1.4 Vitamin names
| Vitamin | Deficiency disease |
|---|---|
| A | Night blindness, xerophthalmia |
| B1 | Beri beri |
| B2 | Ariboflavinosis |
| B12 | Pernicious anaemia |
| C | Scurvy |
| D | Rickets, osteomalacia |
| E | Muscle weakness, sterility |
| K | Increased clotting time, bleeding |
1.5 Nucleic acid facts
A nucleotide has a nitrogenous base, a sugar and a phosphate. The sugar in DNA is 2-deoxyribose and in RNA it is ribose. The bases are adenine, guanine, cytosine and thymine in DNA, while RNA replaces thymine with uracil. In the DNA helix, adenine pairs with thymine through two hydrogen bonds and guanine pairs with cytosine through three, so the two strands run antiparallel and the helix is right handed.