Question

Reading 5' \( \rightarrow \) 3', the sequence of following loops present in the clover leaf structure of t-RNA would be:
(A). Anticodon loop
(B). D-Loop
(C). T\( \psi \)C loop
(D). Variable loop
Choose the correct answer from the options given below:

• A. (B), (A), (C), (D).
• B. (A), (B), (C), (D).
• C. (B), (A), (D), (C).
• D. (B), (D), (A), (C).

Hint:

To remember the sequence of tRNA loops from 5' to 3', trace them clockwise:
Left side is the D-loop (Dihydrouridine).
Bottom side is the Anticodon loop.
Bottom-Right is the Variable loop.
Right side is the T\( \psi \)C loop.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Transfer RNA (tRNA) is an adaptor molecule that bridges the genetic code in mRNA to the amino acid sequence of proteins.
The secondary structure of tRNA is represented by the cloverleaf model, which is organized into highly conserved arms and loops when read sequentially from the 5' end to the 3' end.

Step 2: Detailed Explanation:
Starting from the 5' end and tracing the single-stranded polynucleotide chain to the 3' end, the structural domains are encountered in the following sequence:
1. 5' Terminus: The beginning of the polynucleotide chain.
2. D-Arm and D-Loop (B): The first loop encountered is the D-loop, which contains several dihydrouridine (D) residues.
This loop is important for tertiary structure stabilization and recognition by aminoacyl-tRNA synthetase enzymes.
3. Anticodon Arm and Anticodon Loop (A): After passing the D-arm, the chain continues to the bottom-most loop of the cloverleaf, which is the anticodon loop.
This loop contains seven nucleotides, including the central three-nucleotide anticodon that pairs with the mRNA codon during translation.
4. Variable Loop (D): Positioned immediately after the anticodon arm, this loop varies in length (typically from 3 to 21 nucleotides).
It classifies tRNAs into Class I (short variable loop) or Class II (long variable loop).
5. T\( \psi \)C Arm and T\( \psi \)C Loop (C): The final loop of the cloverleaf contains the conserved sequence ribothymidine (T), pseudouridine (\( \psi \)), and cytidine (C). This domain interacts with the large ribosomal subunit.
6. 3' Acceptor Stem: The structural terminus where the conserved 5'-CCA-3' sequence resides, which binds the specific amino acid.
Tracing the sequence from 5' to 3' yields the sequence: D-Loop (B) \( \rightarrow \) Anticodon loop (A) \( \rightarrow \) Variable loop (D) \( \rightarrow \) T\( \psi \)C loop (C).

Step 3: Final Answer:
The correct sequential loop sequence is (B), (A), (D), (C). This corresponds to option (C).