Transcription in prokaryotes pdf

Prokaryotic Transcription Bacterial transcription or prokaryotic transcription is the process in which messenger RNA transcripts of genetic material in prokaryotes are produced, to be translated for the production of proteins. Bacterial transcription occurs in the cytoplasm alongside translation.

Unlike in eukaryotes, prokaryotic transcription and translation can occur simultaneously. This is impossible in eukaryotes, where transcription occurs in a membrane-bound nucleus while translation occurs outside the nucleus in the cytoplasm. In prokaryotes genetic material is not enclosed in a membrane-enclosed nucleus and has access to ribosomes in the cytoplasm. Transcription is known to be controlled by a variety of regulators in prokaryotes. Many of these transcription factors are homodimers containing helix- turn-helix DNA-binding motifs.

In this form, it can recognize and bind to specific promoter regions in the DNA. The region and the "Pribnow box" region comprise the core prokaryotic promoter, and T stands for the terminator. At this stage, the DNA is double-stranded "closed".

Magendira Mani Vinayagam Academia. IC, VNB. Uridine-5'-triphosphate UTP and cytidine-5'-triphosphate CTP pyrimidine nucleoside triphosphates are disfavoured at the initiation site.

The terminator sequence is usually a palindromic sequence that forms a stem-loop hairpin structure that leads to the dissociation of the RNAP from the DNA template. Page 3. Related Papers RNA synthesis and processing. Both prokaryotes and eukaryotes perform fundamentally the same process of transcription, with the important difference of the membrane-bound nucleus in eukaryotes.

With the genes bound in the nucleus, transcription occurs in the nucleus of the cell and the mRNA transcript must be transported to the cytoplasm. In prokaryotes, which lack membrane-bound nuclei and other organelles, transcription occurs in the cytoplasm of the cell. Prokaryotes use the same RNA polymerase to transcribe all of their genes.

These subunits assemble every time a gene is transcribed, and they disassemble once transcription is complete. Each subunit has a unique role which you do not need to memorize.

The polymerase comprised of all five subunits is called the holoenzyme. Transcription in prokaryotes and in eukaryotes requires the DNA double helix to partially unwind in the region of mRNA synthesis. The region of unwinding is called a transcription bubble. The DNA sequence onto which the proteins and enzymes involved in transcription bind to initiate the process is called a promoter.

In most cases, promoters exist upstream of the genes they regulate. The specific sequence of a promoter is very important because it determines whether the corresponding gene is transcribed all of the time, some of the time, or hardly at all. The structure and function of a prokaryotic promoter is relatively simple Figure 1. One important sequence in the prokaryotic promoter is located 10 bases before the transcription start site and is commonly called the TATA box.

To begin transcription, the RNA polymerase holoenzyme assembles at the promoter. Only one of the two DNA strands is transcribed. As elongation proceeds, the DNA is continuously unwound ahead of the core enzyme as the hydrogen bonds that connect the complementary base pairs in the DNA double helix are broken Figure 2.