Final answer:
A sequence of 9 nucleotides can encode for 3 amino acids, and with 64 possible codons, the total number of different amino acid sequences is 64 x 63 x 62, equaling 249,984. None of the provided options is correct.
Step-by-step explanation:
The question pertains to the number of different amino acid sequences that can be encoded by a sequence of 9 nucleotides long. Since each amino acid is encoded by a group of 3 nucleotides (a codon), a 9-nucleotide sequence can code for 3 amino acids. With 4 different nucleotides available (A, U, C, and G), there are 64 possible codons (4³ combinations). But since we are considering a sequence encoding for exactly 3 amino acids, we need to consider the permutations of these 64 codons taken 3 at a time, without repetition.
This can be calculated as 64 × 63 × 62 (because after choosing one codon for the first amino acid, there are only 63 codons left for the second, and then 62 for the third). Therefore, the total number of different amino acid sequences that can be formed by a 9-nucleotide sequence is 64 × 63 × 62, which is equal to 249,984. Hence, none of the options given (a, b, c, or d) is correct.