If the base sequence of a codon in mRNA is `5'-AUG-3'`, the sequence of tRNA pairing with it must be

Options

A. 5'-UAC -3'
B. 5'-CAU -3'
C. 5'- AUG -3'
D. 5'- GUA -3'

Explanation

To determine the sequence of tRNA that pairs with the mRNA codon `5'-AUG-3'`, we need to follow these steps:

### Step-by-Step Solution:

1. **Identify the mRNA Codon**: The given mRNA codon is `5'-AUG-3'`. This codon consists of three nucleotides: Adenine (A), Uracil (U), and Guanine (G).

2. **Understand Complementarity**: The tRNA anticodon will pair with the mRNA codon based on complementary base pairing rules:
- Adenine (A) pairs with Uracil (U) in RNA.
- Uracil (U) pairs with Adenine (A).
- Guanine (G) pairs with Cytosine (C).

3. **Determine the Anticodon Sequence**:
- For the mRNA codon `5'-AUG-3'`:
- A (from AUG) pairs with U (in tRNA).
- U (from AUG) pairs with A (in tRNA).
- G (from AUG) pairs with C (in tRNA).
- Therefore, the anticodon sequence will be `3'-UAC-5'`.

4. **Write the tRNA Sequence in 5' to 3' Direction**: Since tRNA is typically written in the 5' to 3' direction, we need to reverse the anticodon:
- The anticodon `3'-UAC-5'` becomes `5'-CAU-3'` when written in the 5' to 3' direction.

5. **Select the Correct Option**: Among the provided options, the one that matches our derived tRNA sequence `5'-CAU-3'` is the correct answer.

### Final Answer:
The sequence of tRNA pairing with the mRNA codon `5'-AUG-3'` must be `5'-CAU-3'`.

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