Question

a eukaryotic transcription unit that is 8,000 nucleotides long may use 1,200 nucleotides to make a protein consisting of approximately 400 amino acids. which of the following statements best explains this fact?

many noncoding stretches of nucleotides are present in eukaryotic dna.
there is redundancy in the genetic code.
many nucleotides are needed to code for each amino acid.
there are termination exons near the beginning of the mrna.

Explanation:

1. Analyze Option 1: Eukaryotic DNA has non - coding regions (introns) that are transcribed but then removed during RNA processing (splicing). So a long transcription unit (8000 nucleotides) can have many non - coding nucleotides. The 1200 nucleotides used for the protein are the exons (coding regions) after introns are removed. This explains why a large DNA segment makes a protein from a smaller nucleotide sequence.
2. Analyze Option 2: Redundancy in the genetic code means multiple codons code for the same amino acid. But this doesn't explain the difference in length between the DNA transcription unit and the nucleotide sequence for the protein. It's about codon - amino acid mapping, not the length of non - coding vs coding in DNA.
3. Analyze Option 3: Each amino acid is coded by 3 nucleotides (a codon), so 400 amino acids need about 1200 nucleotides (400×3 = 1200). This option says "many nucleotides are needed to code for each amino acid", which is incorrect as we know the 3 - nucleotide codon system.
4. Analyze Option 4: Termination codons are at the end of the mRNA (to stop translation), not near the beginning. And they don't explain the length difference between the DNA transcription unit and the coding region for the protein.

Answer:

A. Many noncoding stretches of nucleotides are present in eukaryotic DNA.