What role do plasmids play in genetic engineering?

Plasmids are small, circular pieces of DNA that exist independently of chromosomal DNA in bacteria. Their primary role in genetic engineering is their ability to facilitate the incorporation of foreign DNA into an organism. This is achieved through techniques such as transformation, where plasmids can be introduced into bacterial cells, effectively allowing the bacteria to take up and express new genes.

The ability to carry multiple genes enables researchers to manipulate these plasmids in the lab—adding genes of interest, such as those coding for proteins or traits that researchers want to study or utilize. Once inside the host bacterium, the plasmid can replicate independently, ensuring that the introduced foreign DNA is passed on to daughter cells during division. This property makes plasmids invaluable tools for cloning, gene expression, and producing proteins and other products of interest.

The other options do not accurately reflect the primary function of plasmids in genetic engineering. They do not enhance cell respiration or block antibiotic effects directly, nor are they primarily involved in transporting nutrients into bacterial cells, which is a function usually associated with transport proteins or other mechanisms within the bacterial membrane.