Which type of RNA forms the catalytic core of the ribosome and is most abundant by mass in a typical cell?
AmRNA
BtRNA
CmicroRNA
DrRNA
Ribosomal RNA (rRNA) makes up roughly 80% of total cellular RNA by mass. It forms the structural and catalytic scaffold of the ribosome, including the peptidyl transferase center that catalyzes peptide bond formation. mRNA is present in small amounts and is rapidly turned over; tRNA is abundant but less so than rRNA; microRNA is a minor regulatory species.
Question 2 True / False
Because RNA is single-stranded, it cannot form base-paired secondary structures within the same molecule.
TTrue
FFalse
Answer: False
Single-stranded RNA readily folds back on itself, allowing complementary regions to form intramolecular base pairs. This creates stem-loop (hairpin) secondary structures that are essential for function. The anticodon loop of tRNA and the active site of rRNA both depend on precise three-dimensional shapes maintained by internal base pairing. Single-stranded means no second strand is required — not that base pairing is impossible.
Question 3 Short Answer
How does a tRNA molecule physically link a codon in mRNA to the correct amino acid during translation?
Think about your answer, then reveal below.
Model answer: The anticodon loop of tRNA base-pairs with the complementary mRNA codon at the ribosome, while the 3' CCA terminus of the same tRNA carries the corresponding amino acid — tRNA is the physical adaptor bridging nucleotide sequence and amino acid identity.
This adaptor function is why tRNA is indispensable. The genetic code is not a direct chemical affinity between codons and amino acids; it is mediated entirely by tRNA. Each tRNA is aminoacylated by a specific aminoacyl-tRNA synthetase that recognizes both the tRNA's anticodon and the correct amino acid, ensuring the two ends of the molecule are always matched.