What is Transcription?
In general, we all have transcribed something, such as messages or voice mails by writing in a paper or coping in something else. Like wise transcription is nothing but a kind of process in which the information in the molecule is rewritten, so it can be said that transcription is something that we all follow in our daily life, in the same way our cells also has some way of transcribing the proteins and the hereditary information.
Transcription in our cells is carried in a specialised and a narrow manner. However, in biology transcription is defined as the process of copying the information in our DNA, into a sequence of a gene as the component of the RNA.
Transcription is considered as the first step in expression of the gene where the information from a gene is constructed as a functional product in the form of proteins.
The main aim of transcription is to make a copy of RNA, in a DNA sequence of the gene. Considering the protein coding gene, the copy of RNA which is transcript and thus carries an information needed for building a polypeptide which is known as protein or the subunits of protein.
In eukaryotes transcription needs to go through some of the steps of processing before translating into proteins.
Mechanism of Transcription?
Transcription is a process by which the information from one strand is copied to the new molecule which is present in the messenger RNA, which is most commonly called as mRNA.
DNA stably stores the genetic material safely in the nucleic acid of the cells as a template or a reference.
At that time, mRNA is comparable to copy from the reference cell as it carries the similar information which is not a different copy of the DNA segment as its sequence is complementary to the template of the DNA.
Transcription is usually carried out by an enzyme called as RNA polymerase and the number of accessory proteins which are called as Transcription factors.
These Transcription factors helps in binding the specific DNA sequences that are commonly called as enhancers and a promoter sequences, in order to recruit the RNA polymerases in an appropriate transcription site.
Transcription factors and the RNA polymerases forms a complex known as transcription initiation complex.
This complex initiate transcription and the RNA polymerases begins the synthesis of mRNA by matching the complementary bases of the original strand of DNA.
The mRNA molecule is an elongated. Once the strand is synthesised completely, transcription is terminated.
The newly formed mRNA copies of the gene serve as the blue prints for the synthesis of the protein during the process of translation.
Characteristic of Transcription
During the process of transcription, only one strand of the DNA is copied which is known as template strand and here the RNA molecules are single stranded and are called as messenger RNAs (mRNAs).
The DNA strand corresponds the mRNA which is known as coding or sense strand.
Eukaryotes are the organisms which possess a nucleus, the transcription taking part in eukaryotes consists of an initial product known as pre-mRNA, which is extensively edited through splicing before the production of mature mRNA and the translation is being read by ribosomes, which is one of the cell organelles which serves as a site for synthesis of proteins.
Transcription of any one gene takes place at the location of chromosomes in that particular gene, which is relatively a short segment of the chromosome.
The active transcription process in a gene depends on the need for the activity in that particular gene in a specific tissue or a cell at a given time.
Transcription in Prokaryotes
Prokaryotes are the organisms which lacks the nucleus. Many genes in prokaryotes expresses a signal called as operators which are also known as operons, when a specialised protein named repressors bind to the DNA in an upstream which is a start point of transcription to prevent the access of the DNA with the help of RNA polymerase.
These repressor proteins prevent the transcription of the gene by physically blocking the action of the enzyme, RNA polymerase.
Typically, repressors are released from the action of blocking when receiving signals other molecules in the cell indicating that the genes have to be expressed.
Apart from some of the prokaryotes genes expresses signals to which activator proteins which bind to stimulate the transcription.
Transcription in Eukaryotes
Usually, the transcription in eukaryotes is more complicated than prokaryotes. Initially the RNA polymerase in higher organisms is a more complicated enzyme than a relative sub unit enzyme of prokaryotes.
In addition to this there are many accessory factors which helps in controlling the efficiency of the individual promoters.
These accessory proteins are generally called as transcription factors and it typically responds to the signals which arises within the cell that whether the transcription is required.
In many genes of humans many transcription factors are needed before proceeding the transcription which helps in efficient transcription.
Transcription factor either causes repression or activation of the gene while expressing in eukaryotes.
This is the first step in the process of initiation, Here the RNA polymerase binds to the sequence of DNA, which is called as promoter and found near the beginning of the gene.
Where each gene has its own promoter. Once it is bound the RNA polymerases separates the strands of the DNA, which provides the template single stranded for the process of transcription.
Here one strand of the template of the DNA, acts as a template for the enzyme, RNA polymerase. It reads this template in a base in an appropriate time.
The polymerase builds an RNA molecule out of complementary nucleotides, that makes a chain which grows from 5’ to 3’ end.
The transcript RNA carries the same information as the coding non template strand of the DNA, but it contains the Uracil base instead of the thymine(T).
Sequences are called as terminators signals where the RNA transcript is complete. Once they are transcribed, it causes the transcript to be released from the enzyme RNA polymerase.
One such example of a mechanism of termination is involving the formation of a hairpin the RNA.