Question

What are episomes?
A. Hereditary DNA of bacterial cell
B. Extrachromosomal hereditary material of bacteria
C. Modification of the cell membrane performing respiration
D. None of these

Answer 1

Hint: An episome is a part of genetic material that can occur independently of the main genetic material (called the chromosome) and is also able to integrate into the chromosome. Examples of episomes are; insertion sequences, transposons, F factor, and viruses.

Complete answer: An episome is a non-essential genetic element in bacteria. In addition to its independent occurrence, an episome can also occur as an integrated part of the host genome of bacteria. An episome differs from other pieces of DNA that are independent of the chromosome (i.e. plasmids) by their large size. Hereditary DNA of bacterial cells does not occur independently, hence it cannot be called episome. The cell membrane is called the plasma membrane; it does not take part in performing respiration. It is a semi-permeable membrane that allows transport.
Hence, the correct answer is option B, i.e., Extrachromosomal hereditary material of bacteria.

Note: Plasmids are different from episomes, as plasmid DNA is not able to link up with chromosomal DNA. The plasmids have all the information necessary for its independent replication, unlike episomes. Transposons and insertion sequences are examples of episomes. These are also known as mobile genetic elements.