What is transcription and where does it occur?
Transcription is the process of converting DNA sequence into mRNA in the nucleus
of a eukaryotic cell or the cytoplasm of a prokaryotic cell. During transcription, the
enzyme RNA polymerase binds to a specific region of double-stranded DNA known
as the promoter. The RNA polymerase then synthesizes a single-stranded RNA
molecule complementary to one of the DNA strands through base pairing, with the
help of nucleoside triphosphates (NTPs) that provide the energy required for chain
elongation in the growing RNA molecule. As transcription proceeds, a primary
transcript is synthesized with the same sequence as the non-template DNA strand
with the exception that thymine (T) in DNA is replaced with uracil (U) in RNA.
In prokaryotes, transcription occurs in the cytoplasm since there is no nuclear
membrane that separates the DNA from the cytoplasm. Therefore, the transcription
and translation processes may be coupled, meaning that the mRNA produced is
immediately translated into protein. In eukaryotes, however, transcription occurs in
the nucleus and is separated from the cytoplasm by a nuclear membrane. Therefore,
the mRNA must be transported from the nucleus, across the nuclear membrane, and
into the cytoplasm, where it can then be translated to produce proteins.
Transcription is a tightly regulated process as it is the primary way of regulating gene
expression. It can be influenced by various factors, including regulatory proteins,
histone modifications, and non-coding RNAs. Moreover, any error in transcription
can lead to mutations that may cause diseases such as cancer, developmental
disorders, and genetic diseases.
References:
1. Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2014). Molecular
biology of the cell (Vol. 6). Garland Science.
2. Lodish, H., Berk, A., Zipursky, S. L., Matsudaira, P., Baltimore, D., & Darnell, J. (2000).
Molecular cell biology (4th ed.). W.H. Freeman.
3. Lewin, B. (2007). Genes (Vol. 3). Jones and Bartlett Publishers.