What term describes a small circular DNA molecule that exists independently of the main bacterial chromosome and is often used in genetic engineering?

What term describes a small circular DNA molecule that exists independently of the main bacterial chromosome and is often used in genetic engineering?

• A. Chromosome
• B. Plasmid
• C. Ribosome
• D. Mitochondrion

Answer: (B)

Plasmids are small circular, double-stranded DNA molecules that exist independently of the bacterial chromosome and replicate on their own. This independence makes them excellent vehicles for genetic engineering: scientists can insert foreign genes into a plasmid, introduce it into bacteria, and rely on the plasmid’s own replication and selectable markers to propagate and study the gene of interest. Because plasmids are not typically essential for basic survival, bacteria can carry extra genes without losing essential functions, which is precisely why they’re so useful as cloning and expression vectors. In contrast, the bacterial chromosome carries the main genome; ribosomes are the cellular machines for protein synthesis, and mitochondria are energy-producing organelles found in eukaryotic cells, not bacteria.

Plasmids are small circular, double-stranded DNA molecules that exist independently of the bacterial chromosome and replicate on their own. This independence makes them excellent vehicles for genetic engineering: scientists can insert foreign genes into a plasmid, introduce it into bacteria, and rely on the plasmid’s own replication and selectable markers to propagate and study the gene of interest. Because plasmids are not typically essential for basic survival, bacteria can carry extra genes without losing essential functions, which is precisely why they’re so useful as cloning and expression vectors. In contrast, the bacterial chromosome carries the main genome; ribosomes are the cellular machines for protein synthesis, and mitochondria are energy-producing organelles found in eukaryotic cells, not bacteria.