Nucleus

Primary Transcript

Also known as: Pre-mRNA

The immediate, raw output of RNA Polymerase II before any modifications occur.

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• Composition: Contains both Exons (coding) and Introns (non-coding).
• State: Unstable and unprocessed.
• Role: Direct copy of the template DNA strand (with U instead of T).

Nucleus

hnRNA

Heterogeneous Nuclear RNA

A collective term for the diverse mix of high molecular weight RNA found in the nucleus.

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• Composition: A mix of primary transcripts and processing intermediates.
• Why "Heterogeneous"?: Because the transcripts are of vastly different sizes.
• Distinction: Often used interchangeably with pre-mRNA, but strictly refers to the bulk population.

Cytoplasm

mRNA

Messenger RNA

The final, polished product ready for export and translation.

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• Composition: Exons only (Introns removed).
• modifications: Has a 5' Cap and a 3' Poly-A Tail for stability.
• Role: Serves as the template for protein synthesis at the ribosome.