Difference Between Plasmid and Vector

Main Difference – Plasmid vs Vector

Plasmid and vector are two types of double-stranded DNA molecules that have different functions in the cell. The main difference between plasmid and vectors is that plasmid is an extra-chromosomal element of mainly bacterial cells whereas vector is a vehicle that carries foreign DNA molecules into another cell. Plasmids can also be used as vectors. Cosmids, viral vectors, and artificial chromosomes are the other types of vectors. Generally, plasmids and vectors are self-replicative molecules inside the cell. Vectors are mainly used in the recombinant DNA technology to introduce foreign DNA molecules into cells.

Key Areas Covered

1. What is a Plasmid
      – Definition, Structure, Role
2. What is a Vector
     – Definition, Structure, Types, Role
3. What are the Similarities Between Plasmid and Vector
     – Outline of Common Features
4. What is the Difference Between Plasmid and Vector
     – Comparison of Key Differences

Key Terms: Artificial Chromosomes, BAC Vectors, Cloning Vectors, Cosmid, Expression Vectors, Foreign DNA, Plasmid, Viral Vectors, YAC Vectors

What is a Plasmid

Plasmids are extra-chromosomal, self-replicating, double-stranded, circular DNA molecules, generally found in bacterial cells. They can also be found inside archaea and protozoans. They may be encoded for several features such as antibiotic resistance, metal resistance, nitrogen fixation, and toxin production. However, the gene products of plasmids are not necessary for the survival of bacteria under natural conditions. However, plasmids can be used as vectors that carry genetic information to a second cell. A plasmid used as a vector is shown in figure 1.

Figure 1: pBR322

As plasmids are extra-chromosomal elements, they can be readily isolated from bacterial cells. Plasmids consist of an origin of replication. Thus, they are self-replicative molecules inside the host. The unique restriction sites of plasmids can be used to introduce a foreign DNA segment into the plasmids. The insertion of a foreign DNA segment does not alter the replication properties of the plasmid. The transformed cells can be identified using the gene products of the plasmids such as antibiotic resistance.

What is a Vector

Vector refers to a DNA molecule that serves as a vehicle to carry foreign DNA molecules into another cell. The foreign DNA segment can be replicated and/or expressed inside the host. The gene products encoded by the marker genes of the vectors are essential for the identification and characterization of the insertion and expression in the host cell. The four main types of vectors are plasmid vectors, viral vectors, cosmids, and artificial chromosomes. Viral vectors are generally known as bacteriophages. Retroviruses, lentiviruses, and adenoviruses are the three main types of viral vectors. Retroviruses are mainly used to introduce DNA into animal cells. Phages are linear DNA molecules. Packaging and infection by a lentiviral vector are shown in figure 2.

Figure 2: Lentiviral Vector

Cosmids are a type of hybrid vectors that carry properties of both plasmids and phages. They can be used to carry large genes intact. The three types of artificial chromosome vectors are bacterial artificial chromosomes, yeast artificial chromosomes, and human artificial chromosomes. Bacterial artificial chromosomes (BACs) are produced based on the bacterial mini-F plasmid. Yeast artificial chromosomes (YACs) consist of telomeres, a yeast centromere, and selectable marker genes for the identification of the foreign DNA inside the yeast cells. Human artificial chromosomes (HACs) can be used to introduce genes into human cells. They carry the largest DNA segments among other types of vectors.

Vectors can be divided into two based on their function: cloning vectors and expression vectors. Cloning vectors serve as carrier DNA molecules while expression vectors facilitate the expression of foreign DNA segment inside the host.

Similarities Between Plasmid and Vector

• Plasmid and vector are double-stranded DNA molecules.
• Plasmids and most vectors are circular DNA molecules.
• Both plasmid and vector are self-replicative DNA molecules.
• Both plasmid and vector can be used to introduce foreign DNA molecules into cells.

Difference Between Plasmid and Vector

Definition

Plasmid: Plasmids are extra-chromosomal, self-replicating, double-stranded, circular DNA molecules, generally found in bacterial cells.

Vector: Vectors are DNA molecules that serve as vehicles to carry foreign DNA molecules into another cell.

Significance

Plasmid: Plasmids are extra-chromosomal elements, mainly in bacteria.

Vector: Vectors are carrier DNA molecules that carry foreign DNA molecules into another cell.

Types

Plasmid: Plasmids are found in bacteria, archaea, and protozoans.

Vector: Plasmids, cosmids, viral vectors, and artificial chromosomes are the four types of vectors.

Natural/Artificial

Plasmid: Plasmids naturally occur in bacterial cells.

Vector: Vectors naturally occur or artificially-produced by a series of ligation and restriction digestion reactions.

Genes

Plasmid: Plasmids are naturally encoded for antibiotic resistance, nitrogen fixation, metal resistance, and toxin production.

Vector: Vectors carry important genes for the function of the cell.

Gene Product

Plasmid: The gene product of plasmids is not essential for the function of bacterial cells.

Vector: The gene product of vectors is important for the cell.

Conclusion

Plasmid and vector are two types of self-replicative DNA molecules. Plasmids are the extra-chromosomal elements, naturally occurring inside the bacterial cells. Vectors are artificially-introduced DNA molecules into the cells. Plasmids do not carry essential genes for the functioning of the bacterial cells. However, plasmids carry important genes for the functioning of the cell. The main difference between plasmid and vector is the origin and role of each type of DNA molecules.

Reference:

1. “Plasmid/Plasmids.” Nature News, Nature Publishing Group, Available here.
2. Phillips, Theresa. “Learn How Vectors Are Used in Gene Cloning to Create GMOs.” The Balance, Available here.

Image Courtesy:

1. “Lentiviral vector” By Peter Znamenskiy – Own work (Public Domain) via Commons Wikimedia
2. “PBR322” By Ayacop (+ Yikrazuul) – Own work (Public Domain) via Commons Wikimedia