Beauties locked up in an enclosure can neither be recognized nor appreciated. The genetic information in the genome of living organisms when expressed is observed on the physical appearance of the organism. Genetic information is expressed through the process of transcription and translation.
Contents
Transcription is the process whereby information on the gene (a section of the genome) is copied into RNA ribonucleic acid which is later deciphered to produce protein during a process called translation.
Before we go in-depth on the topic. Let’s look at the structural component of the gene of living organisms to be considered in transcription.
The enhancers are short non-coding regions of the DNA on the gene usually of about 50-1500 base pairs recognized by the activator factors also called transcription factors at the initiation step of transcription in eukaryotes. Promoter likewise is a short sequence of DNA where transcription is initiated in prokaryotes. It is located towards the 5’ end of the gene with -35 and -10 sequence respectively.
Introns are the non-coding regions of the gene that do not code for any amino acid and are often removed at the final stage of transcription prior translation while exons are the coding regions of the gene that are left after the remover of the introns that are later translated into protein eukaryotes. Terminator region on the DNA template is another portion of the gene that tells the RNA polymerase to stop making mRNA from DNA template.
RNA polymerase is an enzyme that catalyzes the production of mRNA sequences from DNA. It has four major components:
- Alpha (α) factors
- Beta (β) factors
- Beta prime (β’) factors
- Sigma (σ) factors
The α, β, and β’ factors of the RNA polymerase, also called the core enzyme to ensure that RNA polymerase bind to the DNA while the σ factors are responsible for the ability of RNA polymerase to recognize the promoter sequence DNA and initiate transcription. The combination of these factors in RNA polymerase is called the holoenzyme.
Transcription in living organisms occurs in three steps:
- Initiation
- Elongation
- Termination
INITIATION STEP
RNA polymerase holoenzymes and some transcription factors bind to the promoter region of the gene to form a structure called closed promoter complex. The DNA structure then unwinds to form an open promoter complex, where the two strands are opened. However, only the strand DNA starting from the 5’ is transcribed into mRNA.
RNA nucleotides (Nucleotide trisphosphates (NTPs) are added to form the 5’ strand end for the 3’ strand of DNA template, after which, sigma factor is removed from the RNA polymerase in the promoter region of the DNA strand. This marks the end of the initiation step of transcription.
ELONGATION STEP
At this stage, RNA polymerase moves along the DNA template toward the 3’ end to continue elongation of the growing RNA transcript. As the polymerase travels, it unwinds the DNA template ahead of it and rewinds the DNA templates behind it.
TERMINATION STEP
Termination occurs in two ways in a living organism: rho-independent termination and rho-dependent termination.
When the RNA polymerase reaches the G-C rich hairpin loop structure. The hairpin loop makes the RNA polymerase to slow down and eventually stop. This is called rho-independent termination. It is a common method of termination found in prokaryotes. An alternative method of termination occurs when the RNA polymerase encounters an ATP dependent helicase called Rho –protein thereby leading to the termination of the transcription process. Proofreading of the RNA sequence is carried out by RNA polymerase.
It should, therefore, be noted that the steps explained above are for prokaryotes.
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