Transcription is the name given to the chemical synthesis of RNA
from a DNA
template. In other words, DNA is transcribed in order to make RNA, which is then decoded to produce proteins.
Overview of Transcription
Transcription is the first stage of the expression of genes into proteins. In transcription, a mRNA (messenger RNA) intermediate is transcribed from one of the strands of the DNA molecule. The RNA is called messenger RNA because it carries the 'message' or genetic information from the DNA to the ribosomes, where the information is used to make proteins. RNA and DNA use complementary coding, where base pairs match up, similar to how the strands of DNA bind to form a double helix. One difference between DNA and RNA is that RNA uses uracil in place of the thymine used in DNA. RNA polymerase mediates the manufacture of an RNA strand that complements the DNA strand. RNA is synthesized in the 5' -> 3' direction (as seen from the growing RNA transcript). There are some proofreading mechanisms for transcription, but not as many as for DNA replication. Sometimes coding errors occur.
Steps of Transcription
Transcription may be broken into five stages: pre-initiation, initiation, promoter clearance, elongation and termination.