Answer from: Douglas Lester, PhD, MSc, BSc (Hons)
In order to fit the long, fragile DNA molecule into a microscopic human cell, it has to be carefully packaged and rolled into a protein-containing chromosome. Each human chromosome is a linear piece of DNA, which contains the four-letter alphabet ACGT. Each human chromosome is approximately 100 million letters or bases long.
Chromosome - what is it? How do chromosomes work?
A human chromosome is a DNA molecule with the genetic material of our organism. Most eukaryotic chromosomes include proteins called histones that with the help of proteins, bind to and condense the DNA molecule to maintain its integrity.