Products of transcription: Which RNA species are direct primary products of transcription by RNA polymerase in cells?

Introduction / Context:
Transcription is the synthesis of RNA from a DNA template. Cells produce several functional RNA types, each with a distinct role in gene expression and protein synthesis. Recognizing that multiple classes of RNA arise from transcription clarifies why different RNA polymerases or accessory factors exist in various domains of life.

Given Data / Assumptions:

• RNA polymerase copies DNA into RNA without requiring a primer.
• Different genes encode different noncoding and coding RNAs.
• In bacteria, one RNA polymerase makes mRNA, rRNA, and tRNA; in eukaryotes, multiple nuclear polymerases share this work.

Concept / Approach:
Messenger RNA carries protein-coding information to ribosomes. Transfer RNA delivers amino acids during translation by base pairing with codons. Ribosomal RNA forms the catalytic and structural core of ribosomes. All three originate as transcripts from DNA. Additional RNAs such as small RNAs and snRNAs are also transcription products, but the essential triad mRNA, tRNA, and rRNA are the classical outputs.

Step-by-Step Solution:
Identify the process: transcription produces RNA from DNA. List canonical RNA types synthesized: mRNA, tRNA, and rRNA. Confirm each is transcribed by RNA polymerase. Select the inclusive option.

Verification / Alternative check:
Pulse-labeling and Northern blot experiments detect nascent transcripts corresponding to mRNA, tRNA, and rRNA genes, confirming transcriptional origin for all.

Why Other Options Are Wrong:

• Each individual RNA type alone is incomplete.
• None of these: False because all listed RNAs are products of transcription.

Common Pitfalls:
Assuming only mRNA is transcribed because it encodes proteins; noncoding RNAs are equally essential and also arise from transcription.

Final Answer:
All of these.