Deoxyribonucleic acid is abbreviated as DNA. The smallest part of the chromosome that is self-reproducing, regulates biological functions and transmits heritable characteristics and is capable of causing variation, mutation and evolution of organisms is called DNA. This is called the molecular basis of life. About 90% of the chromosomes of organisms contain DNA. There are two types of nucleotides in the DNA molecule. Exon and Intron Nucleotides. Meaningful parts are called exons and nonsense parts are called introns. The molecular weight of DNA is 106-109 daltons.