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The structure of DNA is important in synthesising specific proteins needed in biological processes.

Not all parts of the DNA code for proteins, there is a coding and non-coding part of DNA, which can switch genes on and off, so variations in these areas may affect gene expression, and if the correct protein is synthesised or not.

The diagram below shows DNA with certain genes switch on and some are switched off:

This diagram shows all of the genes are switched off:

In different cells around the body, genes will be switched on and others will be switched off. This will vary depending on which cells you examine.