Transcription Steps

Transcription is the process where DNA is converted into RNA, a key step in gene expression. Understanding how RNA polymerase binds to DNA and synthesizes RNA helps us grasp the fundamental mechanisms of life at the molecular level.

1. RNA polymerase binds to the promoter region

   • The promoter is a specific DNA sequence that signals the start of a gene.
   • RNA polymerase recognizes and attaches to the promoter, initiating transcription.
   • This binding is crucial for the correct expression of genes.

2. DNA double helix unwinds

   • The DNA strands separate to expose the template strand for transcription.
   • This unwinding is facilitated by the action of RNA polymerase.
   • The unwound region is known as the transcription bubble.

3. Template strand is read

   • RNA polymerase reads the template strand in the 3' to 5' direction.
   • This ensures that the RNA is synthesized in the 5' to 3' direction.
   • The template strand provides the necessary information for RNA synthesis.

4. Complementary RNA nucleotides are added

   • RNA nucleotides pair with their complementary DNA bases (A-U, C-G).
   • This process is guided by the base-pairing rules, ensuring accuracy.
   • The addition of nucleotides occurs as RNA polymerase moves along the DNA.

5. RNA strand elongates

   • The RNA strand grows as more nucleotides are added.
   • Elongation continues until a termination signal is reached.
   • The RNA polymerase catalyzes the formation of phosphodiester bonds between nucleotides.

6. Termination sequence is reached

   • A specific sequence in the DNA signals the end of transcription.
   • This sequence causes RNA polymerase to stop adding nucleotides.
   • The termination sequence ensures that the RNA transcript is of the correct length.

7. RNA polymerase detaches

   • Once the termination sequence is reached, RNA polymerase releases the RNA strand.
   • The enzyme also detaches from the DNA template.
   • This step is essential for the completion of the transcription process.

8. Newly synthesized RNA is released

   • The RNA molecule is now free and can undergo processing (e.g., capping, polyadenylation).
   • The released RNA can be mRNA, tRNA, or rRNA, depending on the gene.
   • This RNA will eventually be used in protein synthesis or other cellular functions.