DNA

• Eukaryotic cells contain linear DNA molecules that exist as chromosomes - thread like structures, each made up of one long molecule of DNA and its associated proteins.
• In eukaryotic cells chromosomes are found in the nucleus.
• In eukaryotic cells the DNA molecule is really long so it has to be wound up so it can fit into the nucleus. It is wound around proteins called histones.

  Histone proteins also help to support the DNA.

  The DNA (and protein) is then coiled up very tightly to make a compact chromosome.
• The mitochondria and chloroplasts in eukaryotic cells also have their own DNA

  This is pretty similar to prokaryotic DNA because its circular and shorter than DNA molecules in the nucleus.

  It is not associated with histone proteins.
• Prokaryotes also carry DNA as chromosomes - but the DNA molecules are shorter and circular.
• In prokaryotes the DNA isn't wound around histones - it condenses to fit in the cell by supercoiling.