Gene is fundamental, physical and functional unit of heredity, which carries information from one generation to the next. Genes are composed of polynucleotides or DNA molecules.
A nucleotide is made up of a nitrogenous base, a phosphate group and a sugar. A nucleoside is made up of nitrogenous base and a sugar molecule.
Histones are basic protein associated with eukaryotic DNA to form chromosomes.
Hydrocarbons are organic substances made up of hydrogen and carbon like petrol, benzene etc.