In the case of prokaryotic transcription, both the processes of transcription and translation occur simultaneously and continuously in the cytoplasm. These processes do not occur simultaneously in eukaryotic transcription. The transcription and translation both occur in the cytoplasm in prokaryotic transcription. However, in eukaryotic transcription, the transcription takes place in the nucleus and the translation occurs in the cytoplasm. The prokaryotic transcription initiation is simple as the DNA is not associated with the histone protein.
In eukaryotic transcription, with the DNA being associated with the protein, the process becomes complex. The RNA processing takes place in the cytoplasm for prokaryotic transcription and in the nucleus for eukaryotic transcription.
Eukaryotic transcription involves three types of RNA. RNA polymerase in prokaryotic transcription has 5 polypeptides. The RNA polymerase is a core enzyme which is having different subunits. Moreover, for this enzyme to work, there are sigma factors. A promoter is a DNA sequence that the transcription machinery attaches to and uses to start transcription.
There are two promoter consensus sequences located in the and regions upstream of the start site, which is the same in all promoters and bacterial species. TATA is the consensus sequence, often known as the region. Polymerase aborts when it is unable to synthesize. Once polymerase is synthesized, i. The transcription of eukaryotes is much more complicated than that of prokaryotes. Eukaryotes need several additional proteins known as transcription factors to first bind to the promoter region and then aid in the selection of the proper polymerase.
The Eukaryotes have 3 RNA polymerase enzymes. The process of elongating a transcription takes a long time. When the resulting protein is no longer needed, transcription stops.
As a result, the primary method to control what type of protein and how much of each protein is expressed in a prokaryotic cell is the regulation of DNA transcription. All of the subsequent steps occur automatically. When more protein is required, more transcription occurs. Therefore, in prokaryotic cells, the control of gene expression is mostly at the transcriptional level. Eukaryotic cells, in contrast, have intracellular organelles that add to their complexity.
The newly synthesized RNA is then transported out of the nucleus into the cytoplasm, where ribosomes translate the RNA into protein. The processes of transcription and translation are physically separated by the nuclear membrane; transcription occurs only within the nucleus, and translation occurs only outside the nucleus in the cytoplasm. The regulation of gene expression can occur at all stages of the process Figure 1.
Regulation may occur when the DNA is uncoiled and loosened from nucleosomes to bind transcription factors epigenetic level , when the RNA is transcribed transcriptional level , when the RNA is processed and exported to the cytoplasm after it is transcribed post-transcriptional level , when the RNA is translated into protein translational level , or after the protein has been made post-translational level.
Figure 1. Prokaryotic transcription and translation occur simultaneously in the cytoplasm, and regulation occurs at the transcriptional level. Eukaryotic gene expression is regulated during transcription and RNA processing, which take place in the nucleus, and during protein translation, which takes place in the cytoplasm. Further regulation may occur through post-translational modifications of proteins.
The differences in the regulation of gene expression between prokaryotes and eukaryotes are summarized in Table 1.
0コメント