TRANSCRIPTION UNIT- It is the collective term used for all the base pairs present on DNA. It helps in the process of transcription.

THESE ARE OF THE FOLLOWING THREE TYPES-

• PROMOTER- These are the base sequences that initiate the process of transcription and are present at 5’ end of the coding strand.
• STRUCTURAL GENE- These are the base sequences present on the template strand which code for the formation of RNA.
• TERMINATOR- These are the base pairs present on the 3’end of the coding strand and stops the process of transcription.

 

PROCESS OF TRANSCRIPTION-

There are three different types of RNA present in a cell

• m-RNA (provides template)
• r-RNA (plays the structural and catalytical role)
• t-RNA (brings amino acids)

The process of transcription takes place in the following three steps-

• INITIATION– In this step RNA polymerase binds at the promoter site along with initiating factor, which is the sigma factor starts the process of transcription.
• ELONGATION– In this step RNA polymerase proceeds the reaction and opens the helical form of DNA due to which DNA gets elongated and the RNA is formed behind the RNA polymerase.
• TERMINATION– In this step, a stopping factor which is RHO factor joins with RNA polymerase due to which it gets separated from DNA, and RNA is formed.

“INTRONS” and “EXONS” are present on the formed RNA.

INTRONS are the base sequences that do not code for a polypeptide chain and are present on Hn-RNA.

EXONS are the base sequences present on the mature messenger RNA which code for a polypeptide chain.