Two differences between the structures of mRNA and tRNA.

Two differences between the structures of mRNA and tRNA.

• A. mRNA has base-pairing; tRNA has no base-pairing; mRNA is circular; tRNA is linear.
• B. mRNA has no base-pairing; tRNA has base-pairing; mRNA is linear; tRNA cloverleaf.
• C. mRNA binds amino acids; tRNA binds to DNA; mRNA is double-stranded; tRNA is single-stranded.
• D. mRNA is identical for all genes; tRNA varies.

Answer: (B)

The key idea is how these two RNA types fold and what that means for their roles. tRNA folds because its sequence forms internal base-pairings, creating stem–loop regions that give it a defined cloverleaf shape (and, in three dimensions, an L-shaped form). This stable intramolecular base-pairing is essential for holding the correct amino acid and for recognizing codons during translation. mRNA, by contrast, is a linear, single-stranded molecule that mainly serves as the template carried from DNA to the ribosome. While it can have some local secondary structures, it does not rely on extensive base-pairing to the same extent as tRNA, and it doesn’t adopt a rigid, cloverleaf shape. So the two differences highlighted are that mRNA is linear and lacks strong intramolecular base-pairing, whereas tRNA has base-pairing that yields the cloverleaf structure. Other statements conflict with how these molecules function: mRNA is not circular, and mRNA does not bind amino acids or DNA; tRNA, not mRNA, is the one that carries amino acids and participates in codon recognition; and mRNA sequences vary between genes rather than being identical.

The key idea is how these two RNA types fold and what that means for their roles. tRNA folds because its sequence forms internal base-pairings, creating stem–loop regions that give it a defined cloverleaf shape (and, in three dimensions, an L-shaped form). This stable intramolecular base-pairing is essential for holding the correct amino acid and for recognizing codons during translation. mRNA, by contrast, is a linear, single-stranded molecule that mainly serves as the template carried from DNA to the ribosome. While it can have some local secondary structures, it does not rely on extensive base-pairing to the same extent as tRNA, and it doesn’t adopt a rigid, cloverleaf shape. So the two differences highlighted are that mRNA is linear and lacks strong intramolecular base-pairing, whereas tRNA has base-pairing that yields the cloverleaf structure.

Other statements conflict with how these molecules function: mRNA is not circular, and mRNA does not bind amino acids or DNA; tRNA, not mRNA, is the one that carries amino acids and participates in codon recognition; and mRNA sequences vary between genes rather than being identical.