DNA coding sequence length determines polypeptide size via triplet code

Steps:

• Double-stranded DNA with 6000 nucleotides means 3000 nucleotides per strand.
• The coding sequence is on one strand, so it contains 3000 nucleotides.
• Transcription yields mRNA with 3000 nucleotides.
• Translation uses 3 nucleotides per codon to specify 1 amino acid, so 3000 / 3 = 1000 amino acids.

Why B is correct:

• The triplet genetic code dictates that 3 nucleotides encode 1 amino acid, so 3000 coding nucleotides produce 1000 amino acids.

Why the others are wrong:

• A: Divides total DNA nucleotides (6000) by 12, ignoring the single coding strand and triplet code.
• C: Assumes the full 6000 nucleotides are the coding sequence, overlooking double-stranded structure.
• D: Assumes 1 nucleotide per amino acid, violating the triplet code.

Final answer: B