Minimum Number of tRNAs Required to Read All Arginine Codons Without Inosine

Arginine is encoded by six codons: CGU, CGC, CGA, CGG, AGA, and AGG. The question is, assuming inosine is not available in the tRNA anticodon, what is the minimum number of distinct tRNAs needed to recognize all these codons?

Understanding Codon Recognition and Wobble Rules

• The genetic code is degenerate, meaning multiple codons can code for the same amino acid.

• The wobble hypothesis explains how fewer tRNAs can recognize multiple codons due to flexible base pairing at the third codon position.

• Inosine (I) in the anticodon can pair with U, C, or A, greatly reducing the number of tRNAs needed.

• Without inosine, tRNAs must rely on strict Watson-Crick base pairing, requiring more tRNAs to cover all codons.

Arginine Codons and Required tRNAs Without Inosine

• The six arginine codons split into two groups based on their first two nucleotides:

  • CGN codons: CGU, CGC, CGA, CGG

  • AGR codons: AGA, AGG

• For CGN codons, the third base varies (U, C, A, G). Without inosine, each third base requires a distinct tRNA anticodon:

  • tRNA anticodons needed: GCI (with inosine), but without inosine, must have separate tRNAs for U, C, A, and G at the wobble position.

  • So, four tRNAs are needed for CGN codons without inosine.

• For AGR codons (AGA and AGG), two additional tRNAs with anticodons complementary to UCU and CCU are required.

Total Minimum Number of tRNAs

• 4 tRNAs for CGN codons

• 2 tRNAs for AGR codons

• Total = 6 tRNAs

Summary Table

Keywords for SEO Optimization

• Arginine codons and tRNA recognition

• Genetic code degeneracy and wobble hypothesis

• tRNA anticodon base pairing rules

• Inosine role in tRNA wobble position

• Minimum tRNA number for arginine codons

• Codon-anticodon interaction without inosine

• Translation and tRNA diversity

• Molecular biology of arginine encoding

• Protein synthesis and tRNA specificity

• Wobble base pairing limitations

Conclusion

Without inosine in the tRNA anticodon, the minimum number of tRNAs required to read all six arginine codons (CGU, CGC, CGA, CGG, AGA, AGG) is six. This is because each codon variant requires a specific tRNA due to the lack of wobble flexibility provided by inosine.

Correct answer: (1) Six