Question

Which of the following statements is true regarding plasmids?
(a) Plasmids are widely used in gene transfer.
(b) These are found in the virus.
(c) Plasmid contains the gene for vital activities.
(d) These are the main part of the chromosome.

Answer 1

Hint: They also bear genes that aid the organism's survival in nature and confer selective advantages such as antibiotic resistance. While chromosomes are huge, they contain all the necessary genetic material required for normal living conditions.

Complete answer: A plasmid is a short, extrachromosomal molecule of DNA inside a cell that can replicate independently and is physically isolated from the chromosomal DNA. They are usually found in bacteria as small spherical, double-stranded DNA molecules; but in archaea and eukaryotic species, plasmids are also present. In nature, plasmids also bear genes that support the body's survival and confer a selective advantage, such as resistance to antibiotics. While chromosomes are large and contain all the important genetic material required for life under normal conditions, plasmids are normally very small and contain only extra genes that may be useful in some cases or circumstances. Plasmids are used as vectors to clone, pass, and control genes. It is possible to inject a DNA fragment carrying the gene of interest into a plasmid vector, and recombinant plasmids are produced. Through transformation, these plasmids are then inserted into a bacterium. Bacteria divide quickly, creating a large number of DNA fragments with genes that are needed. A thin, spherical, dsDNA molecule is a plasmid that is distinct from the chromosomal DNA of a cell and is not part of the chromosome. In bacterial cells and even in certain eukaryotes, but not in viruses, plasmids are normally found. The plasmids bear the genes that give the bacterium genetic benefits, such as antibiotic resistance, not the genes for essential activities.
Therefore, the correct answer is option A.

Note: Inside a cell, it is a small, extrachromosomal DNA molecule that is physically isolated from chromosomal DNA and can independently replicate. They are commonly used in molecular cloning as vectors, helping to guide the replication within host species of recombinant DNA sequences.