Prokaryotes are singled celled organisms and may be referred to as the earliest form of the most primitive life on earth. They include bacterial, prokaryotes and Achaeans. They are able to survive in a variety of environments including extreme habitats like swamps, hot springs, wet lands and the guts of animals. Prokaryotic cells are less complex when compared to eukaryotic cells. They lack a true nucleus and no DNA molecules. The following can be found in the bacterial cell: Capsule, Cell wall, cytoplasm, Plasma Membrane, Pili, Flagella, Ribosomes, Plasmids and the Nucleoid Region. Below is a representation of the Prokaryotic cell.
Figure 1. The Prokaryotic cell
Transcription in Prokaryotes
The process whereby the messenger RHA transcripts of the genetic material of prokaryotes are translated for the production of protein is referred to as Prokaryotic transcription. Transcriptions for bacterial occurs in the cytoplasm. This is not the case with eukaryotes as prokaryotic transcription can take place simultaneously with translation. For eukaryotes, transcription occurs in the membrane-bound nucleus while translation occurs outside the nucleus in the cytoplasm. Transcriptions in prokaryotes is controlled by a variety of factors. Let’s look at the steps that initiates transcriptions in Prokaryotes.
- A holoenzyme is formed through the bonding of the RNA polymerase to one of the several specificity factors σ. In this form, it can identify and get bound to the specific promoter regions in the DNA.
- The DNA becomes single stranded after it is unwound. This DNS structure is referred to as “open complex”.
- The transcription of the DNA is done by the RNA polymerase, producing about 10 abortive transcripts which cannot leave the RNA polymerase because the exit channel is blocked by the σ-factor.
- The σ-factor dissociates from the core enzyme and elongation commences.
This is the translation of messenger RHA to proteins in prokaryotes. How is this initiated?
This process involves the assembly of components of the translation system. These are the ribosomalsubunits (50S & 30S subunits), the mRNAto be translated, the (formyl) aminoacyl tRNA(the tRNA charged with the first amino acid), GTP(as a source of energy), and three initiation factors(IF1, IF2, and IF3) which supports the assembly of the initiation structure.
The ribosome is made up of three sites. The A, P and E sites. The point of entry for the amino acyl tRNA is the A site. The formation of the peptidyl tRNA takes place in the P site while the exit site for the unchanged tRNA after losing its amino acid to the developing peptide chain. The site for initiation depends on the communication between the 30S subunit and the mRNA template.
The mRNA template combines with the 30S sub unit at the purine-rich region upstream of the AUG initiation codon. During the formation of this complex, nucleotide sequences pair form a double stranded RNA structure that combines the mRNA to the ribosome in such a manner that the initiation codon is placed at the P site.
Figure 2, The Prokaryotic Translation Process
Here is a tabular difference.
This is the synthesis of RNA from a DNA template.
The Synthesis of proteins from an mRNA template.
The aim is to make RNA copies of individual genes that the cell can use in the biochemistry.
This is to synthesise and used for lots of cell function.
mRNA, tRNA, rRNA and non-coding RNA