<P> Bacterial chromosomes tend to be tethered to the plasma membrane of the bacteria . In molecular biology application, this allows for its isolation from plasmid DNA by centrifugation of lysed bacteria and pelleting of the membranes (and the attached DNA). </P> <P> Prokaryotic chromosomes and plasmids are, like eukaryotic DNA, generally supercoiled . The DNA must first be released into its relaxed state for access for transcription, regulation, and replication . </P> <P> In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called chromatin . This allows the very long DNA molecules to fit into the cell nucleus . The structure of chromosomes and chromatin varies through the cell cycle . Chromosomes are even more condensed than chromatin and are an essential unit for cellular division . Chromosomes must be replicated, divided, and passed successfully to their daughter cells so as to ensure the genetic diversity and survival of their progeny . Chromosomes may exist as either duplicated or unduplicated . Unduplicated chromosomes are single double helixes, whereas duplicated chromosomes contain two identical copies (called chromatids or sister chromatids) joined by a centromere . </P> <P> Eukaryotes (cells with nuclei such as those found in plants, fungi, and animals) possess multiple large linear chromosomes contained in the cell's nucleus . Each chromosome has one centromere, with one or two arms projecting from the centromere, although, under most circumstances, these arms are not visible as such . In addition, most eukaryotes have a small circular mitochondrial genome, and some eukaryotes may have additional small circular or linear cytoplasmic chromosomes . </P>

Where are chromosomes found in a plant cell