The DNA sequence is ATG. What would be the sequence of bases in anticodon of tRNA
A. CAU
B. AUG
C. UAC
D. TAC

Understanding tRNA Anticodon Base Pairing with mRNA Codons

Base pairing between codons and anticodons is a fundamental aspect of protein synthesis. During translation, the sequence of bases in mRNA codons determines the order of amino acids in the growing polypeptide chain. Each codon is recognized by a specific tRNA anticodon, ensuring that the correct amino acid is added to the chain. In this article, we will explore the correct anticodon sequence for the codon ATG, explain the base pairing mechanism, and clarify why the correct answer is UAC.

Correct Answer:

The correct anticodon sequence for the codon ATG is UAC (Option C).

What is a Codon and an Anticodon?

A codon is a sequence of three nucleotide bases on mRNA that specifies a particular amino acid during protein synthesis. A tRNA anticodon is a complementary three-base sequence on the tRNA molecule that pairs with the codon in a specific manner based on the rules of base complementarity.

Base Pairing Rules

The base pairing between codons and anticodons follows the following principles:

• Adenine (A) pairs with Uracil (U) in RNA (instead of thymine in DNA).
• Cytosine (C) pairs with Guanine (G).
• The interaction is stabilized by hydrogen bonds between complementary bases.

Example:

• Codon: ATG (on mRNA)
• Anticodon: UAC (on tRNA)

How tRNA Anticodons Work

1. Codon Recognition:

   • The ribosome reads the codon on the mRNA strand.
   • Each codon corresponds to a specific amino acid.

2. Anticodon Binding:

   • The anticodon on the tRNA molecule binds to the complementary codon on mRNA via hydrogen bonding.
   • The anticodon ensures that the correct amino acid is delivered to the ribosome.

3. Peptide Bond Formation:

   • The amino acid attached to the tRNA is incorporated into the growing polypeptide chain.
   • The ribosome catalyzes the formation of a peptide bond between amino acids.

Why UAC is the Correct Answer

1. Codon-Anticodon Base Pairing

• The codon ATG on mRNA is transcribed as AUG during transcription.
• The anticodon that pairs with AUG follows complementary base pairing rules:
  • A → U
  • U → A
  • G → C
• Therefore, the anticodon sequence is UAC.

2. Start Codon

• ATG is the start codon for protein synthesis.
• It codes for the amino acid methionine (Met), which initiates translation.

3. Complementary Pairing

Why Other Options Are Incorrect

(A) CAU

• Incorrect because C would not pair with A in mRNA.
• The correct complementary base for A is U in RNA.

(B) AUG

• AUG is the codon sequence, not the anticodon.
• Anticodons are complementary to codons, so AUG cannot pair with itself.

(D) TAC

• TAC is the DNA sequence that would code for AUG during transcription.
• Anticodons are RNA sequences, so T would be replaced by U in RNA.

Role of Anticodon in Protein Synthesis

1. Translation Initiation

• The start codon AUG signals the beginning of protein synthesis.
• The tRNA carrying methionine recognizes AUG using the anticodon UAC.

2. Elongation

• After the start codon is recognized, tRNAs carrying amino acids continue to bind to codons on mRNA.
• The ribosome catalyzes the formation of peptide bonds.

3. Termination

• When a stop codon is reached, translation ends.
• The completed polypeptide is released from the ribosome.

Importance of Codon-Anticodon Pairing

Ensures accuracy in protein synthesis.
 Prevents insertion of incorrect amino acids.
 Maintains the correct reading frame.

Common Issues with Codon-Anticodon Pairing

1. Wobble Hypothesis

• Flexibility at the third codon position allows for pairing with multiple anticodons.
• This explains why some codons code for the same amino acid.

2. Mismatched Codon-Anticodon

• Incorrect pairing can result in amino acid substitution.
• This leads to dysfunctional or misfolded proteins.

3. Frameshift Mutations

• Insertion or deletion of nucleotides can disrupt the reading frame.
• This results in incorrect amino acid sequence.

Applications of Codon-Anticodon Interaction

1. Genetic Code Deciphering

• Understanding codon-anticodon pairing helped decode the genetic code.
• It revealed the universality of the triplet codon system.

2. Gene Editing and Therapy

• Antisense RNA and siRNA therapies target specific codons.
• These approaches rely on codon-anticodon base pairing.

3. Biotechnology

• Codon optimization improves gene expression in recombinant protein production.
• Rare codons are replaced with frequently used ones to enhance protein synthesis.

Conclusion

Base pairing between codons and anticodons is essential for accurate protein synthesis. The codon ATG codes for methionine and is recognized by the tRNA anticodon UAC. Understanding the principles of complementary base pairing helps in genetic research, gene therapy, and biotechnology. Proper codon-anticodon pairing ensures the correct sequence of amino acids in proteins, maintaining cellular function and genetic integrity.