Structures of the DNA Molecule and of Chromosomes

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HONORS BIOLOGY / BIOLOGY
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DNA is a large molecule and ranges in size from just a few nucleotides (usually paired with a complimentary strand in a double helical form) in length to a chain (polymer) of tens of millions of nucleotides. Notice in the image below that the two complimentary strands run in opposite directions, an orientation called anti-parallel. Click on the image below to see a larger version.

The multi-level structure of a chromosome is shown in the image below--click on it to see a larger version. Remember, DNA in most eukaryotic cells only adopts this super compact chromosome form when the cell is going through mitosis--the rest of the time (interphase), the DNA is less tightly wound and packed.

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