The most abundant RNA in metabolically active mammalian cells is rRNA. This holds true for cells like HeLa or other rapidly dividing types, where protein synthesis demands high ribosome numbers.​

Option Analysis

mRNA (A) carries genetic code from DNA to ribosomes for protein synthesis but comprises only 1-5% of total RNA due to its transient nature and low copy numbers per transcript.​
rRNA (B) forms the core of ribosomes, enabling translation, and accounts for 80-85% of total RNA to support massive ribosome production in active cells.​
snoRNA (C) guides modifications on other RNAs like rRNA in the nucleolus but remains minor, with most at low levels (often <1% total RNA).​
tRNA (D) delivers amino acids during translation and makes up 10-15% of total RNA, far less than rRNA.​

RNA Composition Table

In metabolically active mammalian cells, the most abundant type of RNA in a metabolically active mammalian cell is ribosomal RNA (rRNA), comprising 80-85% of total cellular RNA. This dominance stems from the cell’s need for ribosomes to drive protein synthesis during high metabolic activity.​

Why rRNA Leads in Abundance

rRNA forms the structural backbone of ribosomes, with multiple types (like 18S, 28S in eukaryotes) associating with proteins. In rapidly growing cells, such as HeLa lines, rRNA synthesis by RNA polymerase I meets the demand for millions of ribosomes per cell. This makes rRNA essential for translation, outpacing other RNAs.​

Comparing Other RNA Types

• mRNA: Only 1-5% of total RNA; heterogeneous and short-lived, with ~12,000 transcripts per cell but low individual copies.​

• tRNA: 10-15%; numerous species (~400 types) ferry amino acids, but total mass lags behind rRNA.​

• snoRNA: Minimal fraction; ~475 types modify rRNA/tRNA in nucleoli, peaking at low TPM levels across tissues.​

Typical distribution in eukaryotic cells confirms rRNA’s supremacy for metabolic vigor.​

CSIR NET Relevance

For exams like CSIR NET Life Sciences, recognize rRNA’s role in molecular biology—its abundance reflects cellular priorities in protein production over messaging or modification. Active cells amplify this via rDNA clusters.​