The goal of transcription is to make an RNA copy of a gene. This RNA can direct the formation of a protein or be used directly in the cell. All cells with a nucleus contain the same exact genetic information. As discussed, only a small percentage of the genes are actually being used to make RNA at any given time in a particular cell. The transcription process is very tightly regulated in normal cells.
Genes must be transcribed at the correct time.
The RNA produced from a gene must be made in the correct amount.
ONLY the required genes should to be transcribed.
Turning transcription off is just as important as turning it on.
You can picture this as a sophisticated production line, like you would find in a factory. You would want the assembly line working when you needed the product and shut down when you no longer needed the product.
Human chromosomes contain an enormous amount of information. Each chromosome is composed of a single extremely long piece of DNA comprised of millions of nucleotides. An individual gene occupies just a small stretch of a chromosome.
Shown in the animation below is the organization of the DNA in a chromosome. The DNA is tightly coiled and looped to take up less space, just like winding thread on a spool. The chromosome shown below has been copied or replicated and has a characteristic X shape. Chromosomes look like this prior to cell division.
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