Plasmid: Properties, Types of Plasmid, and Characteristics

By BYJU'S Exam Prep

Updated on: November 14th, 2023

Plasmid is a small, circular DNA molecule that exists independently alongside the chromosomal DNA in certain bacteria and other organisms. It is a versatile genetic element that plays a crucial role in various biological processes. Plasmids can replicate autonomously and are capable of transferring genetic information between cells, making them valuable tools in genetic engineering and biotechnology research. Their ability to carry and express specific genes has made them widely used in the production of recombinant proteins, gene therapy, and the study of gene function.

Plasmids can be classified into different types based on their characteristics and functions. One common classification is based on their mode of replication. There are two main types of plasmids: conjugative plasmids and non-conjugative plasmids. Conjugative plasmids possess the ability to transfer genetic material between bacterial cells through a process called conjugation. They carry specific genes, known as transfer genes, that facilitate the transfer process. On the other hand, non-conjugative plasmids lack the ability to undergo conjugation but can still replicate independently within the host cell. These plasmids often carry genes that confer selective advantages to the host, such as antibiotic resistance or the ability to metabolize specific compounds.


Plasmid is a type of self-replicating extrachromosomal DNA molecule. This DNA molecule can carry a few to several hundred genes. A plasmid can be used to multiply protein codes and cloning micro DNA segments. Plasmids can also be designed artificially through the cloning method by inserting any gene inside the bacterial cells. A plasmid can be used to perform multiple functions, such as monitoring chemical levels in an environment, producing synthetic viruses, producing protein in large amounts, etc.

Types of Plasmid

Broadly put, there are two types of plasmids – conjugative and non-conjugative. A conjugative plasmid can promote sexual conjugation between cells through the transfer of genes. On the other hand, non-conjugative plasmids are incapable of conjugation and can only be transferred through conjugative plasmids. Classification of plasmids can also be done based on their incompatibility groups and functions. Here are the main types of plasmids –

  • Resistance plasmids – Also known as R-factors, these plasmids contain genes that offer resistance against antibiotics.
  • Fertility plasmids – These plasmids contain Tra genes that are capable of conjugation.
  • Virulence plasmids – They convert bacterium into pathogens.
  • Degradative plasmids – These help with the digestion of unusual substances, such as salicylic acid and toluene.
  • Col plasmids – This plasmid carries proteins that can kill other bacteria.

Characteristics of Plasmid

Understanding the characteristics of plasmids provides valuable insights into their role in genetic processes, their applications in genetic engineering, and their impact on host cell behavior. Plasmids are distinct genetic elements characterized by their circular, supercoiled, and double-stranded DNA structure. Here are some key characteristics of plasmids:

  • Replication and Gene Carrying: Plasmids have the unique ability to replicate on their own, independent of the host cell’s chromosomal DNA. They always carry at least one gene, which can confer specific traits or functions to the host organism.
  • Double-Stranded DNA: Plasmids consist of double-stranded DNA, where two strands of nucleotides are intertwined. This characteristic ensures stability and efficient gene expression within the plasmid.
  • Varied Copy Numbers: The number of plasmids that can exist in an individual cell can vary greatly, ranging from just one to hundreds. The copy number of plasmids determines the abundance of specific genes and their impact on the host organism.
  • Types of Plasmids: There are diverse types of plasmids, each with unique characteristics and functions. Some common types include Col Plasmids, which encode colicin toxins that provide a competitive advantage; Fertility F Plasmids, responsible for conjugation and gene transfer; Resistance Plasmids, carrying genes that confer resistance to antibiotics; Degradative Plasmids, involved in the breakdown of specific compounds; and Virulence Plasmids, associated with the pathogenicity of certain bacteria.
  • Size and Replicating Genes: Plasmids can vary in size, ranging from small to large molecules. Generally, larger plasmids tend to have fewer replicating genes, as they require more resources and energy for replication.

Properties of Plasmid

Plasmids, which are small circular pieces of DNA, have some interesting properties that make them unique. Following are some of these properties of plasmid:

  • Independent Replication: Plasmids can make copies of themselves inside a cell independently of the cell’s own DNA. They act like little self-replicating machines, ensuring that they are maintained and passed on to daughter cells during cell division.
  • Carrying Genes: Plasmids always carry at least one gene, which is a section of DNA that provides instructions for making specific proteins. These genes can give the host organism new abilities or traits, such as resistance to antibiotics or the ability to break down certain substances.
  • Circular Structure: Unlike the cell’s main DNA, which is in the form of long, linear strands, plasmids have a circular shape. This circular structure helps them to be more stable and less prone to damage.
  • Varying Numbers: The number of plasmids present in a single cell can vary. Some cells may have only one or a few plasmids, while others can have many copies. This difference in numbers can affect how much of a particular protein the cell produces.
  • Different Types: There are various types of plasmids, each with its own characteristics and functions. For example, some plasmids can transfer themselves between different cells, allowing them to spread their genes to other bacteria. Other plasmids may carry genes that help bacteria survive in challenging environments.
  • Size Differences: Plasmids can come in different sizes, ranging from small to large. Larger plasmids often have fewer genes involved in replication, as it requires more resources and energy to copy them.

Functions of Plasmid

Plasmids have a variety of functions. With their ability to replicate, they can be used for cloning important genes and substances. Here, we have shared some of the many important functions of the plasmid:

  • Plasmids can help in the production of large amounts of protein that can be used for various purposes. Moreover, the plasmid can also produce a glowing protein that can be tracked inside a cell.
  • A plasmid can be used to generate synthetic viruses for use in research.
  • Scientists use plasmids to monitor the chemicals present in an environment.
  • Plasmids can offer genetic advantages to bacteria.

Significance of Plasmid

Plasmids are considered some of the most significant microorganisms because they have allowed scientists to make some commendable discoveries. Here are some reasons why plasmid is considered significant –

  • They allow scientists to study the movement of proteins in a cell.
  • With the help of plasmid, scientists are able to put foreign DNA into bacteria.
  • They transfer DNA with antibiotic resistance properties.
  • Plasmid has contributed significantly to the development of molecular biotechnology.

Artificial Plasmid

There are two types of plasmid – natural and artificial. While natural plasmid exists naturally, artificial plasmids are generated in a lab by scientists. The construction of an artificial plasmid happens by recombining unique segments of two more plasmids. The plasmids selected for the recombining process can be natural or artificial in nature.

The development of synthetic plasmids happens in a laboratory where new plasmids are introduced to a host cell for replication. Through the process of artificial plasmid generation, scientists are able to transfer gene-modifying information into cells.

Difference Between Natural Plasmid vs. Artificial Plasmid

The major difference between natural and artificial plasmids are:

Natural Plasmid Artificial Plasmid
It occurs naturally. It is generated in laboratories by scientists.
Natural plasmids are transferred from one bacterium to another. Artificial plasmids are generated by recombining the segments of two or more plasmids.
Natural plasmids can have limitations such as poor marker genes, too stringent, etc. The artificial plasmid can be modified as per requirements and is used to overcome the limitations of the naturally-occurring plasmid.

Plasmid UPSC

Plasmids are small, circular DNA molecules found in bacteria and other organisms. They play a significant role in genetic engineering, as they can be manipulated and used as vectors to introduce foreign DNA into cells. The topic of Plasmid holds importance in the UPSC exam, particularly in the field of biotechnology and genetic engineering.

Understanding the structure, functions, and applications of plasmids is crucial for candidates to comprehend the advancements in genetic research, biopharmaceutical development, and the impact of biotechnology on agriculture, environment, and medicine

Plasmid UPSC Question

Candidates can check to the sample questions provided below on the topic of Plasmids and their types to enhance their understanding. Checking UPSC previous year question papers can also help candidates to understand the pattern and types of questions that have been asked in the exam in relation to this topic.

Question: Which of the following is not a type of plasmid? (A) F plasmid, (B) R plasmid, (C) mRNA plasmid, (D) Virulence plasmid

Answer: (C) mRNA plasmid

Question: Which type of plasmid is commonly used in genetic engineering for the production of recombinant proteins? (A) F plasmids, (B) R plasmids, (C) Expression plasmids, (D) Transposons

Answer: (C) Expression plasmids

Question for UPSC Mains: Discuss the role and significance of plasmids in genetic engineering. Explain the various types of plasmids commonly used as vectors in recombinant DNA technology.

Question for UPSC Mains: Examine the applications of different types of plasmids in biotechnology and their impact on agriculture, healthcare, and environmental sustainability. Discuss the potential benefits and concerns associated with the use of plasmids in these fields.

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