Ok so; Most bacterial chromosomes contain a circular DNA molecule. There is no free endings to the DNA. If there was a free ending to the DNA it would otherwise create a significant challenges to the cells with respect the DNA replication and stability. For the cells that don't contain chromosomes with DNA ending or telomeres (most eukaryotes), have a acquired elaborate mechanisms to overcome these challenges. but however the small circular DNA molecule is called a plasmid. hope this helps you!!