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Chromosome Structure

Before going any further, let’s look at the structure of the DNA as it exists in a cell. If you could remove the DNA from one of your cells and stretch it out, it would be approximately one meter long. How can so much DNA fit into a microscopic cell? The answer is in the packaging. DNA is highly organized into a structure called a chromosome. The chromosome is made up of DNA and proteins. The DNA double helix is wrapped around proteins known as histones, and the histones form complexes called nucleosomes (see Figure 5.3). The nucleosomes are further packaged into supercoiled loops sometimes called solinoids. These are packaged into chromosomes.

Human cells contain 23 pairs of chromosomes (46 total). Certain genetic diseases can be diagnosed by examining the chromosome. This is what is done when a pregnant woman has an amniocentesis. The field of biology that studies chromosomes is called cytogenetics.
Levels of DNA packaging

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