Transcription in Prokaryotes & Eukaryotes; Comparison of Prokaryotic & Eukaryotic RNA Polymerases
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- How Transcription takes place? The actual process and steps are not yet fully understood in humans but to understand we have to study the process of transcription first to get a reasonable understanding. Then we will compare it with Eukaryotes to get a good knowledge.
- in Transcription only a part of DNA is transcribed.
- RNA Polymerase binds to the Promotor but not to the coding region.
- The gene to be transcribed has a double stranded DNA structure but only one strand is transcribed that is called the Template strand.
- The mRNA complimentary to this Template strand.
- Coding strand of the gene is NEVER used.
- The mRNA produced is identical to the Coding strand but, as we all know there is no Thymine (DNA only), so Thymine (T) is replaced by Uracil (U) in the mRNA.
Q: Is Promotor region Transcribed?
Ans: NO. RNA Polymerase starts at +1
Comparison of RNA Polymerases in Prokaryotes and Eukaryotes
Prokaryotic RNA Polymerase
- Single RNA Polymerase (α2ββ’)
- Requires sigma(σ) to initiate at a promoter
- Sometimes requires rho(ρ) to terminate
- Inhibited by rifampin, Actinomycin D
Eukaryotic RNA Polymerase
- RNAP 1: rRNA (nucleolus). Except 5S rRNA
- RNAP 2: hnRNA/mRNA and some snRNA
- RNAP 3: tRNA,, 5S rRNA
- No sigma, but transcription factors (TFIID) bind before RNA polymerase
- No rho required
- RNAP2 inhibited by α amanitin (mushrooms). Actinomycin D
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