Question

What is true of plasmid?
A. Found in viruses
B. Contains genes for vital activities
C. Part of nuclear chromosome
D. Widely used in gene transfer

Answer 1

Hint: A plasmid is a small, circular piece of DNA that is present in certain prokaryotic organisms. It is also found in archaea and some multicellular organisms. Plasmid carry genes that enhance the survival of an organism. It defends the host cell by producing toxins. The structure of plasmid contains the following regions- origin of replication, antibiotic resistance gene, primer binding site and multiple cloning sites.

Complete explanation:
Option A found in viruses: Plasmids are a small circular, double-stranded DNA mostly found in bacteria. They are transferred from one bacterium to another through conjugation. Plasmid is not present in viruses.
Option A is incorrect.
Option B contains genes for vital activities: Plasmid contains genes that are different from the chromosomal DNA present in the nucleus. The plasmid enhances the survival of the organism but does not take part in growth of the organism. Vital activities such as replication, production of proteins, respiration etc are governed by nuclear DNA.
Option B is incorrect.
Option C part of nuclear chromosome: Plasmids are separate from the nuclear chromosome and replicate independently of it. They carry only a small number of genes and are passed between different bacterial cells through conjugation.
Option C is incorrect.
Option D widely used in gene transfer: The ability of plasmid to replicate independently makes it an excellent cloning vector in the recombinant DNA technology for transferring and manipulating genes. Plasmids are also used to amplify or produce many copies of certain genes. This option is correct.
Option D is correct.

So, the correct answer is option D. Widely used in gene transfer.

Note:
Plasmids are of different types namely the fertility f-plasmids, resistance plasmids, co1 plasmids, degenerative plasmids and virulence plasmids. A plasmid acts as a vector that can transport foreign genetic material from one cell to another cell. It has the ability to clone short segments of DNA. Plasmids are used extensively in the biotechnological sector to produce large amounts of antibiotics, proteins, hormones, enzymes etc.