| | Re: Does DNA make up a chromosome?
A chromosome is a single, extended, double-stranded DNA molecule. In many prokaryotes, the "chromosome" is circular, but formally chromosome only applies to the linear DNA molecules that make up the nuclear genome of eukaryotes.
In the cell, DNA is associated with many proteins, including histones, transcription factors, modifying enzymes etc. So cytologically, each chromosomes is a mixture of a single dsDNA molecule and proteins. In a non-dividing (interphase) cell the chromosomes are loosely packed in the nucleus. The X-shape can only be seen in the metaphase of mitosis. This is because before mitosis, each chromosome has been replicated and the two sister chromosomes are connected to each other at the centromere. The DNA-protein of the chromosomes has been condensed at this stage and we see the traditional X (or Y-shape for acrocentric chromosomes), where each half of the X is one sister chromosome. In the anaphase, the two daughter chromosomes separate and migrate to opposite poles of the cell, thus ensuring that the daughter cells each receive a full complement of genetic material.