How does transcription occur in plant cells?

Transcription in plant cells is the process by which the genetic information stored in DNA is copied into messenger RNA (mRNA). This is the first step of gene expression, and it happens mainly in the nucleus.

Here’s how transcription takes place, step by step:

1. Initiation
   • The enzyme RNA polymerase binds to a specific region of the DNA called the promoter (located before the gene).
   • The DNA double helix unwinds and separates at that region, exposing one strand as a template strand.
   • In plants, special transcription factors help RNA polymerase attach to the promoter correctly.
2. Elongation
   • RNA polymerase moves along the DNA template strand, reading the sequence of bases (A, T, G, C).
   • It builds a complementary RNA strand by pairing:
     • A (in DNA) with U (in RNA)
     • T (in DNA) with A (in RNA)
     • G with C, and C with G
   • As RNA polymerase moves forward, the newly formed mRNA strand grows longer while the DNA behind it rewinds.
3. Termination
   • When RNA polymerase reaches a termination signal (a specific sequence on the DNA), transcription stops.
   • The newly made pre-mRNA is released from the DNA template.
4. Post-transcriptional modification (in eukaryotic plant cells)
   • The pre-mRNA undergoes processing before it leaves the nucleus:
     • A 5′ cap is added to the beginning (for protection and ribosome binding).
     • A poly-A tail is added at the end (for stability).
     • Introns (non-coding regions) are removed, and exons (coding regions) are joined together in a process called splicing.
   • The final mature mRNA is then transported out of the nucleus into the cytoplasm for translation.

In summary:

• Transcription converts DNA → mRNA.
• It occurs in the nucleus.
• The key enzyme is RNA polymerase.
• The result is a processed mRNA molecule ready to direct protein synthesis.