Expert: Dana Krempels, Ph.D. - 5/8/2009

Question
what is the name of DNA in different stages of cellular cycle? Most of the time,
chromosomes are used even though they are not suppose to.

When can I use chromatin? What do people mean when they talk about DNA
molecules, is that the same as chromosomes?

Answer
Dear Angela,

When a cell is not actively dividing, the chromosomes exist in their loose, functional form, known as chromatin.  They are still chromosomes, and present in their usual number as linear strings of DNA associated with protein, but they are not readily visible if the cell is stained and mounted on a microscope slide during this phase of the cell cycle (interphase).

During active mitosis or meiosis, the chromosomes become visible as individuals.  Chromosomes are always chromosomes, but when they are not supercoiled in preparation for mitosis, they are found in the form we call chromatin.

A DNA molecule is *part* of a chromosome (in fact, it's the main part), but it's not all there is in a chromosome.  The eukaryotic chromosome is a long strand of DNA wound on protein "spools" that keep it organized, and are involved in which genes on the particular chromosomes are expressed (i.e., which ones are read by the cell and used to make protein) at any given stage in the cell's lifetime.

Hope this helps.

Dana