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The Location of DNA

In human cells, molecules of deoxyribonucleic acid, also known as DNA, are densely packaged into thread-like structures called chromosomes in the nucleus. A small amount of DNA is also found outside the nucleus in organelles called mitochondria.

There are 23 pairs of chromosomes in the nucleus of each human cell. Each chromosome contains one very long DNA molecule. To allow it to fit in the nucleus, the DNA molecule is coiled around proteins called histones and folded many times.

On the left is a spherical animal cell that is open as though it has been cut into two. Inside the cell is a pink circle labeled as the nucleus. Inside the nucleus are blue X-shaped structures. A blue beam from one of these blue structures leads to an enlarged copy of the structure labeled as a chromosome. A looping thread-like blue line comes out from the bottom right corner of the chromosome and expands into a twisted, colorful double helix labeled DNA.

Figure 1. The Location of DNA in Human Cells

Most, but not all, cells contain DNA bundled in a cell nucleus in this way. Mature red blood cells and some cells in the skin, hair, and nails have no nucleus.