Stages of Protein Synthesis : Transcription and Translation

What is Transcription?

It is the process of formation of mRNA from a DNA template.

MECHANISM :

Transcription involves DNA Replication, through which mRNA is formed.

•  Enzyme Helicase unwinds and unzips the two strands of DNA,by breaking the hydrogen bonds between the nitrogenous bases(purine and pyrimidine).
• The exposed ends of the nucleotides represents the Replication fork.
• SSBP (Single Strand Binding Protein) holds the two strands apart, thus prevents twisting of the strands.
• DNA Polymerase III builds new DNA strand by adding nucleotide in 5′ to 3′ direction.
• Since the direction of construction is from 5′ to 3′, the strand is called leading strand and is continous.
• The lagging strand 3′ to 5′ direction is discontinous and the fragments are called Okazaki Fragments.
• Enzyme Ligase connects/seals the Okazaki fragments, thus forming a continous strand.
• Enzyme Primase synthesizes RNA primer at 5′.
• DNA Polymerase I removes and replaces RNA Primer with DNA nucleotides.

 

Thus, mRNA is synthesized.