Biomolecules
Class 12 Chemistry · Chemistry Part II · Chapter 5
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Summary
Biomolecules are the complex organic molecules that build and run living systems: carbohydrates, proteins, nucleic acids and lipids, along with vitamins and hormones. Carbohydrates are optically active polyhydroxy aldehydes or ketones, or compounds that yield these on hydrolysis; they are classed as monosaccharides (glucose, fructose), oligosaccharides such as disaccharides (sucrose, maltose, lactose) and polysaccharides (starch, cellulose, glycogen). Glucose, an aldohexose, exists in open-chain and cyclic hemiacetal (pyranose) forms whose anomers differ at the anomeric carbon. Proteins are polymers of about twenty alpha-amino acids joined by peptide bonds; ten are essential and must come from the diet. Proteins have primary, secondary (alpha-helix and beta-pleated sheet), tertiary and quaternary structures, and lose biological activity on denaturation when these higher structures are disrupted. Enzymes are highly specific protein biocatalysts that lower activation energy. Vitamins are essential dietary factors classed as fat soluble (A, D, E, K) or water soluble (B group and C), and their deficiency causes specific diseases. Nucleic acids, DNA and RNA, are polymers of nucleotides made of a base, a pentose sugar and a phosphate; DNA stores genetic information as a double helix while RNA carries out protein synthesis. Hormones act as chemical messengers regulating body functions.
Carbohydrates: classification and structureGlucose, fructose and disaccharidesProteins, amino acids and structureEnzymes and denaturationVitamins and their deficienciesNucleic acids, DNA, RNA and hormones
Key terms
Monosaccharide
A carbohydrate that cannot be hydrolysed to a simpler sugar, e.g. glucose or fructose.
Glycosidic linkage
The oxygen bridge joining two monosaccharide units, formed by loss of water.
Peptide bond
The -CO-NH- amide linkage joining amino acids in a protein chain.
Denaturation
Loss of a protein's secondary and tertiary structure and biological activity by heat or pH change.
Enzyme
A protein biocatalyst that is highly specific and lowers the activation energy of a reaction.
Nucleotide
The repeating unit of nucleic acids, made of a base, a pentose sugar and a phosphate group.
Extra questions & answers
Try one from this chapter
Carbohydrates are chemically defined as: