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🧬 TRANSCRIPTION – DEGREE LEVEL EXPLANATION

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🔹 1. Definition

Transcription is the biological process by which the genetic information in DNA is copied into messenger RNA (mRNA).

🧠 It’s the first step of gene expression, occurring in the nucleus (eukaryotes) and cytoplasm (prokaryotes).

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🔹 2. Central Dogma of Molecular Biology

DNA → RNA → Protein
Transcription is the DNA → RNA step.

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🔹 3. Types of RNA Produced

• mRNA – messenger RNA (used in translation)
• tRNA – transfer RNA
• rRNA – ribosomal RNA
• Others: snRNA, miRNA (not directly translated)

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🔹 4. Key Enzyme: RNA Polymerase

• In prokaryotes: One RNA polymerase (with σ-factor for initiation)
• In eukaryotes:
  • RNA Pol I → rRNA
  • RNA Pol II → mRNA
  • RNA Pol III → tRNA

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🔹 5. Steps of Transcription

a. Initiation

• RNA polymerase binds to the promoter region (e.g., TATA box in eukaryotes).
• DNA unwinds, and transcription bubble forms.

b. Elongation

• RNA polymerase moves along the template strand (3′ to 5′).
• Synthesizes RNA in 5′ to 3′ direction.
• Uses ribonucleotides (ATP, UTP, GTP, CTP).

c. Termination

• Prokaryotes: Rho-dependent or independent mechanisms
• Eukaryotes: Poly-A signal triggers cleavage and polyadenylation

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🔹 6. Post-Transcriptional Modifications (in Eukaryotes)

1. 5′ Capping – methylated G added
2. Poly-A Tail – 100–250 adenines at 3′ end
3. Splicing – introns removed, exons joined

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🔹 7. Differences: Transcription in Prokaryotes vs Eukaryotes

Feature	Prokaryotes	Eukaryotes
Location	Cytoplasm	Nucleus
RNA Polymerase	One type	Three types
mRNA Processing	No	Yes (capping, tailing, splicing)
Transcription & Translation	Simultaneous	Separated

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🧪 INTERACTIVE MODEL OF TRANSCRIPTION (HTML + CSS + JS)

🔧 Components Visualized:

• DNA (template & coding strands)
• RNA polymerase
• mRNA synthesis
• Promoter region

Transcription Model

DNA to mRNA (Interactive Simulation)