What is a plasmid? a. an organelle found in many bacteria and certain eukaryotes b. a circular DNA molecule that replicates independently of the main chromosome(s) c. a type of virus that has a DNA genome and infects certain types of human cells, including lung and respiratory tract tissue d. a type of virus that has an RNA genome, codes for reverse transcriptase, and inserts a cDNA copy of its genome into cells

Verified step by step guidance

1. Identify the definition of a plasmid: A plasmid is a small, circular, double-stranded DNA molecule that is distinct from a cell's chromosomal DNA.
2. Understand the replication process of plasmids: Plasmids replicate independently of the chromosomal DNA.
3. Recognize the common hosts of plasmids: Plasmids are most commonly found in bacteria but can also be present in archaea and eukaryotic organisms.
4. Distinguish plasmids from viruses: Plasmids are not viruses and do not have the capability to infect cells like viruses do.
5. Select the correct option based on the provided definitions and characteristics of a plasmid.

Key Concepts

Plasmid Structure

A plasmid is a small, circular DNA molecule that exists independently of chromosomal DNA within a cell. It is primarily found in bacteria, but can also be present in some eukaryotic organisms. Plasmids often carry genes that provide advantageous traits, such as antibiotic resistance, and can replicate autonomously, allowing for rapid gene transfer between cells.

Plasmid Function

Plasmids play a crucial role in genetic engineering and biotechnology. They can be used as vectors to introduce foreign DNA into host cells, facilitating the study of gene function and the production of proteins. Their ability to replicate independently allows for the amplification of inserted genes, making them valuable tools in molecular biology.

Differences from Viruses

Unlike viruses, which require a host cell to replicate and often have complex structures, plasmids are simple, self-replicating DNA molecules. Viruses can have either DNA or RNA genomes and typically infect host cells to propagate, while plasmids exist freely within the cytoplasm of bacteria and some eukaryotes, functioning independently of the host's chromosomal DNA.