Overview of Transcription
As we saw, the central dogma of molecular biology is that DNA makes RNA, and RNA makes proteins. The process of making RNA from DNA is called transcription, and it is the major control point in the expression of genes and the production of proteins.
In the use of genetic information, one of the strands of the double-stranded DNA molecule is transcribed into a complementary sequence of RNA. The RNA sequence differs from DNA in one respect: The DNA base thymine (T) is replaced by the RNA base uracil (U). Of all the DNA in a cell, only some is transcribed. Transcription produces all the types of RNA-mRNA, tRNA, rRNA, snRNA, miRNA, and siRNA. New types of RNA and new functions for it are found every year.
The details of RNA transcription differ somewhat in prokaryotes and eukary-otes. For example, the process is much more complicated in eukaryotes, involv-ing a large number of transcription factors. Most of the research on the subjecthas been done in prokaryotes, especially E. coli, but some general features are Kamp/Phototake found in all organisms except in the case of cells infected by RNA viruses.
Although many differences exist between transcription in prokaryotes and eukaryotes, and even differences between transcription of different types of RNA in eukaryotes, some aspects are constant. Table 11.1 summarizes the main features of the process.
Transcription is the process of using a DNA template to produce RNA.
Many types of RNA are produced, such as messenger RNA, transfer RNA, ribosomal RNA, micro RNA, small interfering RNA, and small nuclear RNA.
A primer is not needed for RNA synthesis.
As does all polynucleotide synthesis, the reaction proceeds in the 5' to 3' direction.