Question

If you have 5 nucleotides, say A, T, G, C and X, how many triplet codons you could have formed from it ?

• A. 50
• B. 125
• C. 250
• D. 1250

Hint:

In nature, using four standard nucleotides (A, U, G, C) to form triplet codons yields $4^3 = 64$ unique codons, which is more than enough to specify the twenty standard amino acids.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The genetic code uses combinations of nucleotide bases to specify amino acids.
A codon consists of a specific sequence of three consecutive nucleotides (a triplet).
Key Formula or Approach:
For a system using $n$ different nucleotides to form codons of length $r$, the total number of unique combinations possible with replacement is:
\[ \text{Total combinations} = n^r \]

Step 2: Detailed Explanation:
We are given:
- Number of unique nucleotides available ($n$) = $5$ (A, T, G, C, and X).
- Length of each codon ($r$) = $3$ (since they are triplet codons).
At each of the three positions in the triplet codon, any of the five available nucleotides can be placed.
- Number of choices for the first position = $5$
- Number of choices for the second position = $5$
- Number of choices for the third position = $5$
Using the fundamental counting principle, the total number of unique triplet codons that can be formed is:
\[ \text{Total codons} = 5 \times 5 \times 5 = 5^3 = 125 \]

Step 3: Final Answer:
The total number of triplet codons that can be formed from 5 nucleotides is 125, which corresponds to option (B).