1.    Transcription (DNA to mRNA) :-
Transcription is the first step segment in protein of synthesis one of the two strands takes of place DNA in into nucleus.

2.   It is the process of copying genetic information of a catalyzed by RNA polymerase.
During the process, a part of DNA (a specific gene) uncoils and unzipped by breaking the hydrogen bonds between the two strands. However, only one strand which is in 3' to 5' direction, acts as a template strand or sense strand to synthesize mRNA.

3.   The other strand is called antisense strand.

4.   The nitrogen bases of template strand attract complementary nitrogen bases. A attracts U, T attracts A, G attracts C and C attracts G.

5.   After the formation of ribose sugar phosphate backbone synthesis of mRNA is completed in 5' to 3' direction.

6.   In eukaryotes, the process is catalyzed by the enzyme RNA polymerase II and the mRNA synthesized is called precursor mRNA (pre-mRNA).

7.   It requires processing to become mature functional mRNA molecule. During processing, the capping enzyme adds a guanine nucleotide, most commonly 7-methyl guanosine to the 5' end.

8.   The cap is essential for the ribosome to bind to 5' end of mRNA.

9.   At the 3' end a sequence of about 50 to 250 adenine nucleotides is added. It is called poly (A) tail. It is essential to determine stability of mRNA.

10.                Initially coding sequence (exons) is not continuous.

11. It is interrupted by non-coding sequence (introns).

12.                The introns are removed and the exons are joined so that continuous coding sequence is available. This process is called mRNA splicing.

13.                In prokaryotes, only one type of RNA polymerase synthesizes mRNA and it is capable of functioning directly as mature mRNA, hence, its processing is not required.
Thus, the genetic information present on DNA (on specific gene) to synthesize a specific protein is transcribed on to mRNA which then leaves the DNA, passes through nuclear pore and enters the cytoplasm. The two strands of DNA recoil. If mRNA molecules are produced in excess, they are stored in nucleolus.
The mRNA acts as a messenger as it carries transcribed genetic information or "message" from DNA to This genetic information is nothing but copy of a specific sequence of nitrogen bases of a gene. Is always carried in triplet nitrogen bases called codons each of which codes for a specific amino acid. However, for any mRNA first or initiation codon is always AUG which always codes for methionine in and formyl methionine in prokaryotes. The last codon does not code for any amino acid, hence it is called stop codon. It is one of the three codons UAA, UAG or UGA.

3) TRANSCRIPTION IN PROKARYOTES

4) TRANSCRIPTION IN EUKARYOTES