Question

A gene contains 141 codons. How many nucleotides are present in the gene's coding sequence? How many amino acids are expected to be present in the polypeptide encoded by this gene?

• A. 423 & 141
• B. 420 & 140
• C. 415 & 135
• D. 400 & 110

Hint:

Always convert codons to nucleotides by multiplying by 3.
Unless a stop codon is specifically designated as non-coding in the text, assume a direct $1:1$ codon-to-amino-acid translation ratio.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The transfer of genetic information from a gene to a functional protein relies on a triplet-based coding system.
A codon represents a distinct sequence of three adjacent nucleotides on an mRNA strand.
During translation, each codon is matched with a specific amino acid by transfer RNA molecules.
This basic biological standard implies a direct linear conversion between nucleotides, codons, and amino acids.
Key Formula or Approach:
The primary mathematical conversions are defined as follows:
The total count of nucleotides in the sequence is calculated by:
\[ \text{Total Nucleotides} = \text{Number of Codons} \times 3 \]
The expected number of amino acids in a simple direct-translation system is equal to the number of coding codons:
\[ \text{Number of Amino Acids} = \text{Number of Codons} \]

Step 2: Detailed Explanation:
Let us apply the molecular genetics formulas to the given values.
We are given that the gene contains 141 codons in its coding sequence.
First, we find the absolute number of nucleotides by multiplying the codon count by the codon size of 3:
\[ 141 \times 3 = 423 \text{ nucleotides} \]
This gives us a unique, exact value of 423 nucleotides for the coding sequence.
Second, we evaluate the number of amino acids translated from these 141 codons.
In molecular biology, a translation process generally reads each codon to append a corresponding amino acid.
While natural systems feature a terminal stop codon that does not code for an amino acid, standard examinations assume a direct $1:1$ ratio of codons to amino acids to test structural knowledge.
Thus, 141 codons are expected to yield 141 amino acids.
Since there is no option for 423 nucleotides and 140 amino acids, the value pair 423 & 141 is the correct selection.

Step 3: Final Answer:
The sequence contains 423 nucleotides, and the resulting polypeptide contains 141 amino acids.