Question

Explain the process of transcription in prokaryotes. How is the process different in eukaryotes?

Answer 1

Transcription:

Transcription is the cellular process by which DNA segments are copied into RNA.

Transcription in prokaryotes:

1. Transcription in prokaryotes occurs in the cytoplasm. In prokaryotes, it occurs in three phases- Initiation, elongation, and termination.
2. In the initiation phase, RNA polymerase recognizes a promoter site on the DNA strand. Reading a promoter sequence unwinds the DNA strand and initiates transcription.
3. The core enzyme of RNA polymerase then proceeds to synthesize RNA in the 5'-3' direction. It uses the antisense strand of DNA as the template for RNA synthesis.
4. The 3'-OH group of the growing RNA chain interacts with the α phosphate group of the incoming nucleotide to form a phosphodiester bond.
5. Transcription occurs until a termination sequence on the DNA is found.
6. When the RNA polymerase detects a termination sequence, it stops the transcription process, releases the synthesized RNA transcript, and dissociates from the DNA.

Note:

1. The -10 sequence is referred to as the Pribnow box. It interacts with the sigma factor of RNA polymerase.
2. The -35 sequence -TTGACA is essential for the unwinding of DNA.

Transcription in prokaryotes:

1. Transcription is a continuous process and occurs in the cytoplasm.
2. Only one type of RNA polymerase is used to synthesize RNA molecules.
3. No post-transcriptional modifications occur and the mRNA is devoid of a 5' guanosine cap and a poly A tail.

Transcription in eukaryotes:

1. Transcription is a separate process and occurs in the nucleus.
2. Three types of RNA polymerase enzymes are involved in the eukaryotic transcription process.
3. The mRNA produced has an RNA cap at the 5' end and a poly-A tail at the 3' end.

Transcription in prokaryotes	Transcription in eukaryotes
Transcription is a continuous process and occurs in the cytoplasm.	Transcription is a separate process and occurs in the nucleus.
Only one type of RNA polymerase is used to synthesize RNA molecules.	Three types of RNA polymerase enzymes are involved in the eukaryotic transcription process.
No post-transcriptional modifications occur and the mRNA is devoid of a 5' guanosine cap and a poly A tail.	The mRNA produced has a RNA cap at the 5' end and a poly-A tail at the 3' end.