Some bacterial strains contain many plasmids and some contain none. Plasmids are often used in genetic engineering as cloning vectors. Any enzyme that adds subunits to chains of macromolecules. Example is DNA polymerase. A segment of DNA near the beginning of a gene that controls if and when the gene is actually expressed.
Promoters can be specific for certain tissues such as roots, seeds, etc.
Proteins constitute the enzymes and many of the structural components of cells. The study of the structure and function of proteins. In classical genetics, an organism containing a combination of alleles different from either parent Def. In molecular genetics, a DNA molecule containing a novel sequence. Restriction enzymes were key to making genetic engineering possible.