What Kinds of Genes Do Plasmids Have?

Plasmids are circular rings of genetic material not found on a chromosome. These genetic structures typically contain accessory genes that provide beneficial services to a host cells. Plasmids also have backbone genes that provide a structure, delivery method and proliferation system that enables the accessory genes to continue to provide their function.

Backbone Genes

Backbone genes could be considered the inactive part of a plasmid. This genetic material plays a role in the replication, maintenance and preservation of the plasmid. Backbone genes can also help to transfer the plasmid between host cells. This genetic material is typically preserved among members of the same family of plasmids, allowing for the categorization of plasmids into various groups. One established method for categorizing plasmids is according to their full-length DNA sequence.

Backbones Can Be Engineered with Certain Features

Some research laboratories use plasmid backbones with interchangeable parts. These engineered backbones often have several common features -- including prefix and suffix segments, a replication origin and antibiotic resistance. The backbone sequence starts with the prefix and ends with a segment called the suffix. These structures flank the active part of the plasmid. The replication origin is the segment of the plasmid that activates the plasmid’s self-replication during cell growth and division. The backbones can also be engineered to convey antibiotic resistance.

Accessory Genes

Plasmids also contain accessory genes that encode proteins often beneficial to a host cell. These proteins can be used to break down environmental pollutants or offer protection against some other type of threat. As the name indicates, accessory genes are not required for the secure replication or transport of the plasmid. They are not always necessary for the continued existence of the host, either. However, they can offer functions that are crucial to survival of the host in specific environments. Some accessory genes simply give the host cell an advantage over others.

Types of Plasmids

Several types of plasmids exist, and they have have various functions. Cloning plasmids are used to ease the cloning of DNA fragments. Expression plasmids can be used to push gene expression in various cell types. Gene knockdown plasmids are used to mitigate the expression of a host’s endogenous gene. Reporter plasmids are used for examining the function of genetic elements. Viral plasmids use technology based on viruses to assist in the delivery of genetic material into targeted cells.

About the Author


Photo Credits

  • Dynamic Graphics/Creatas/Getty Images