Microinjection refers to the process of using a glass micropipette to insert substances at a microscopic or borderline macroscopic level into a single living cell. It is a simple mechanical process in which a needle roughly 0.5 to 5 micrometers in diameter penetrates the cell membrane and/or the nuclear envelope. The desired contents are then injected into the desired sub-cellular compartment and the needle is removed. Microinjection is normally performed under a specialized optical microscope setup called a micromanipulator. The process is frequently used as a vector in genetic engineering and transgenics to insert genetic material into a single cell. Microinjection can also be used in the cloning of organisms, and in the study of cell biology and viruses. Microcapillary and microscopic devices are used to deliver DNA into a protoplast.