The mRNA of the hypothetical plant gene HSDU is 800 nucleotides long and encodes a 160-amino-acid protein. The coding sequence (CDS) length is calculated as 480 nucleotides, since each amino acid is specified by a 3-nucleotide codon (160 × 3 = 480), excluding untranslated regions (UTRs).​

CDS Calculation

The CDS spans from the start codon (AUG) to the stop codon, translating directly into the protein sequence. With 160 amino acids, the CDS requires exactly 480 nucleotides (160 codons × 3 nucleotides/codon), as the genetic code uses triplet codons universally. The full mRNA length of 800 nt includes 5′ and 3′ UTRs (320 nt total), which do not code for protein but regulate translation and stability.​

Why Not Other Lengths?

Common misconceptions yield wrong values:

• 477 nt: Assumes stop codon excluded (159 codons + start), but CDS includes stop codon.​

• 483 nt: Adds extra for plant-specific features, but standard calculation ignores this for hypothetical genes.​

• 800 nt: Confuses full mRNA with CDS; UTRs account for the difference.​

• 160 nt: Mistakenly uses 1 nt per amino acid, violating triplet code.​

The HSDU gene CDS length calculation reveals key molecular biology principles for CSIR NET and GATE Life Sciences aspirants. This hypothetical plant gene’s mRNA is 800 nucleotides long, encoding a protein of 160 amino acid residues, making HSDU CDS length a perfect triplet codon problem.​

Understanding CDS in Plant Genes

Coding sequence (CDS) is the mRNA portion from start codon (AUG) to stop codon (UAA/UAG/UGA), translated into protein. Each of the 20 amino acids uses a 3-nucleotide codon from 64 possible triplets, ensuring degeneracy but fixed 3 nt/aa ratio. For HSDU, 160 residues need 160 codons, so CDS = 480 nt. Remaining 320 nt are UTRs for stability and translation efficiency in plants.​

Step-by-Step HSDU CDS Calculation

1. Identify protein length: 160 amino acids.

2. Apply genetic code: 3 nucleotides per codon.

3. Multiply: 160 × 3 = 480 nucleotides.

4. Verify: Full mRNA (800 nt) minus UTRs confirms CDS exclusion.​

This matches exam patterns in CSIR NET Life Sciences, emphasizing no introns in mature mRNA.​

Common Errors in CDS Length Exams

• Forgetting stop codon: Yields 477 nt (incorrect).

• Including UTRs: Gives 800 nt (full mRNA).

• Plant-specific adjustments: No evidence for HSDU; stick to standard.​

Mastering HSDU gene CDS length calculation boosts scores in genetics sections for competitive exams.