Question

A gene is 8,001 nucleotides in length. Studies of this gene show that it encodes a protein only 400 amino acids long – far shorter than the 2,667 amino acids that were expected. This is best explained by the fact:

nucleotides often break off and are lost during the transcription process.

the genetic code is ambiguous (unclear).

in some cases, many nucleotides are used to encode a single amino acid.

many of the 8,001 nucleotides of the gene are ultimately noncoding.

Answer 1

In the eukaryotic genome, the coding region of DNA codes for protein/ RNA whereas non-coding regions don't code for proteins. In eukaryotes, genes contain exons (coding region) and introns (non-coding regions) and introns are spliced after transcription and mature mRNA having only exons are formed.

The correct answer is "many of the 8,001 nucleotides of the genes are ultimately non-coding." Most of the fraction of the eukaryotic genome is comprised of non-coding DNA sequences. These non-coding regions play major role in gene regulation. A gene of 8,001 nucleotide length codes for a protein of 400 amino acids which is much shorter than the expected nucleotide length because it contains both exons and introns. After transcription, introns are removed and mature mRNA contains only exons which is the reason for having a protein of 400 amino acid and not of the expected size (2,667 amino acid).

Nucleotide often breaks off and lost during the transcription process is not the right answer because transcription is a highly regulated process. Random loss of nucleotide during transcription will lead to a change in nucleotide sequences which in turn will affect the amino acid sequence due to mutation. Changes in the nucleotide sequence will lead to the formation of non-functional proteins or no protein formation.

The genetic code is ambiguous is not the right answer. The genetic code is clear but redundant which means more than one codon codes for an amino acid.

In some cases, many nucleotides are used to encode a single amino acid is not the right answer. Due to genetic code degeneracy, more than one codon codes for an amino acid but amino acids are incorporated irrespective of the number of their occurrence when their specific codon encountered during protein synthesis.