| 环境 |
DNA The principal material of inheritance. It is found in chromosomes and consists of molecules that are long unbranched chains made up of many nucleotides. Each nucleotide is a combination of phosphoric acid, the monosaccharide deoxyribose and one of four nitrogenous bases: thymine, cytosine, adenine or guanine. The number of possible arrangements of nucleotides along the DNA chain is immense. Usually two DNA strands are linked together in parallel by specific base-pairing and are helically coiled. Replication of DNA molecules is accomplished by separation of the two strands, followed by the building up of matching strands by means of base-pairing, using the two halves as templates. By a mechanism involving RNA, the structure of DNA is translated into the structure of proteins during their synthesis from amino acids |
