What are plasmids

A. made of RNA.
B. found only in single copies within bacteria.
C. small self-replicating DNA molecules in bacteria.
D. necessary in order for bacteria to reproduce.
E. non-circular DNA segments in bacteria.



  1. 0 Votes

    The answer is C. Plasmids are DNA molecules that can replicate independently of the chromosomal DNA, and is usually found in bacteria. They can also be found in all the three major domains: Archea, Bacteria, and Eukarya. 

  2. 0 Votes

    Plasmids are very small, circular DNA molecules.  They have the ability to replicate independently of a genome in ones body, and can be found one to a cell or hundreds, which is called the copy number.  Plasmids are known to carry genes for antibiotic resistance in the body.  Since antibiotic resistance is becoming more and more prominent in the medical world these days, it’s very important to have plasmids in your body.  They have taken on important roles in Molecular Biology today because of their antibiotic resistance qualities and their high copy numbers.

  3. 0 Votes

    I have to say I take issue with the answer option C.  While plasmids are small circular DNAs independent from the bacterial genome, they do NOT replicate themselves.  Plasmids do not have any machinery for replication, and require cellular machinery to replicate.

    In addition, humans do not generally have plasmids in their body. We have a linear genome (2 x 23 pairs of chromosomes).  While there are some plasmids that are stable inside cells, in general someone would have to be given this DNA plasmid as part of a treatment (like for gene therapy) to have a plasmid inside them, or be infected with a virus that puts the plasmid inside a human cell.  Additionally, you do not want to have antibiotic resistance in your body.  The antibiotics that we use frequently do not attack the human body, but do attack the bacteria that is infecting us. In special cases of dire need, they may give antibiotics that do affect the cellular machinery of humans, but only when there is no other option.

    Plasmids do have antibiotic resistance genes in them, and it is what allows scientists (myself included) to exploit bacteria to make DNA and proteins that we can study.  We give the bacteria a plasmid that encodes the item we want to study with a resistance gene on it.  We then put the bacteria under pressure of that antibiotic, if the bacterial cells did not pick up those plasmids they will die.  Those bacteria that picked up the plasmid will survive and help us do our research.

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