The chromosomes within our cells contain an enormous amount of information. It is estimated that humans have somewhere around 30,000 genes. Each gene codes for an RNA molecule that is either used directly or used as a guide for the formation of a protein such as the insulin shown earlier. Information in our cells generally flows in a predictable order from the storage form of the information (DNA) through the working form (RNA) into the final product (protein). This pathway is used by all organisms and is diagrammed below.
As shown, DNA is used as a guide or template for the production of more DNA. This process, known as replication, is addressed in the section on cell division.
The process in which particular sections of DNA (genes) are used to produce RNA is known as transcription. We will cover transcription in some detail because alterations in the transcription of certain genes are very important in the development of cancer.
The set of genes that are 'on' at any given time is critical. The variable environment in which we live means that different genes need to be 'on' at different times. For example, if a meal contains large amounts of lactose, a sugar found in milk, then our bodies respond by turning on (transcribing) the genes that lead to the production of enzymes that break down lactose. If a different sugar or nutrient is present, the correct genes need to be turned on to process it.
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