细菌的主要结构和功能是由染色体控制的,而一些非主要特征则由于独立的复制子(称为质粒)的存在而产生的。质粒(plasmids)是染色体外的环状双链DNA。它能独立于染色体而稳定存在。然而,许多质粒还可能与染色体共价结合,成为染色体环的一个组成部分。质粒大小,从分子量为一百万(只能编码二、三 The major structures and functions of bacteria are controlled by chromosomes, while some of the non-essential features arise from the presence of independent replicons (called plasmids). Plasmids are extrachromosomal circular double-stranded DNA. It can exist independently of chromosomes. However, many plasmids may also be covalently bound to chromosomes and become part of the chromosomal loop. Plasmid size, from a molecular weight of one million (can only encode two, three