what is the difference between transcription of rna polymerase in eukaryotes ans prokaryotes
There are several differences between the transcription of RNA polymerase in eukaryotes and prokaryotes:
1. RNA polymerase in prokaryotes consists of a core enzyme composed of five subunits, while eukaryotic RNA polymerase consists of three distinct enzymes (RNA polymerase I, II, and III) composed of up to 16 subunits.
2. Eukaryotic RNA polymerases require more transcription factors for initiation compared to prokaryotic RNA polymerase.
3. In eukaryotes, RNA polymerase II transcribes protein-coding genes, while RNA polymerase I transcribes ribosomal RNA genes and RNA polymerase III transcribes transfer RNA and some other small RNA genes. In contrast, prokaryotic RNA polymerase transcribes all types of genes.
4. Eukaryotic transcription is more complex due to splicing, the addition of a 5' cap and a 3' poly-A tail, and chromatin remodeling. Prokaryotic transcription is simpler and does not involve these processes.
5. Eukaryotic genes have introns, while prokaryotic genes do not.
6. Eukaryotic transcription requires RNA processing, which occurs in the nucleus. Prokaryotic transcription and translation occur simultaneously in the cytoplasm.
The transcription process of RNA polymerase differs between eukaryotes and prokaryotes in several ways. Here are the key differences:
1. Complexity of Gene Structure: Eukaryotic genes are usually more complex than prokaryotic genes. Eukaryotic genes contain both coding regions called exons and non-coding regions called introns. During transcription, the entire gene is transcribed, including both exons and introns. After transcription, introns are removed through a process called RNA splicing, and exons are joined together to form the final mRNA transcript. In contrast, prokaryotic genes typically lack introns, and the entire gene is transcribed directly into mRNA without the need for splicing.
2. Transcription Factors: Eukaryotes require the involvement of transcription factors for gene transcription to occur. Transcription factors are proteins that bind to specific sequences in the DNA to facilitate the binding of RNA polymerase to the promoter region of the gene. These factors are necessary because eukaryotic DNA is tightly wrapped around histone proteins, forming a complex structure called chromatin. Transcription factors help in the unwinding of this chromatin structure to expose the DNA strand for transcription. In prokaryotes, transcription is typically initiated by RNA polymerase binding directly to the promoter region without the need for additional transcription factors.
3. RNA Polymerase Variants: Eukaryotes have three different RNA polymerases (RNA Pol I, II, and III) which transcribe different types of genes. RNA polymerase I transcribes most of the ribosomal RNA (rRNA) genes, RNA polymerase II transcribes protein-coding genes (mRNA), and RNA polymerase III transcribes various small RNA genes. In contrast, prokaryotes have a single RNA polymerase that can transcribe all types of genes.
4. Capping and Polyadenylation: After transcription, eukaryotic mRNA undergoes additional modifications to become functional mRNA. These modifications include the addition of a 5'-cap structure at the beginning of the mRNA and a poly(A) tail at the 3'-end. These modifications are important for mRNA stability, nuclear export, and translation. In prokaryotes, mRNA molecules lack these modifications.
In summary, the main differences in transcription between eukaryotes and prokaryotes involve gene structure, the involvement of transcription factors, the types of RNA polymerases, and the modifications that occur after transcription.