Final answer:
mRNA sequences with different codons might be identical because the genetic code is redundant, allowing multiple codons to specify the same amino acid. Codons must be at least three nucleotides long to encode the 20 amino acids due to the limited number of nucleotide combinations with shorter sequences. The genetic code's universality and redundancy facilitate the translation of mRNA into proteins across diverse living organisms.
Step-by-step explanation:
- Explanation for Identical mRNA Sequences with Different Codons
The sequences for mRNA1 and mRNA2 may be identical even if their codons differ due to the redundancy of the genetic code. In many cases, different codons can code for the same amino acid because multiple codons can specify the same amino acid. This redundancy is also known as the 'wobble' position, where the third nucleotide in a codon may vary without altering the amino acid it codes for. For example, the codons UCG and UCU both code for serine despite the third base difference.
- Why Codons Must Be At Least Three Nucleotides Long
The need for codons to be at least three nucleotides long arises from the necessity to encode 20 amino acids. If codons were only one or two nucleotides long, there would not be enough unique codons to represent all the amino acids. With four RNA nucleotides to choose from (A, C, G, and U), there are 64 possible triplet codons (43), which is more than enough to encode all 20 amino acids, with some redundancy allowing for a degree of error tolerance in the genetic code.
- Redundancy and Universality of Genetic Code
The genetic code is both universal and redundant. Universality means that virtually all living organisms use the same genetic code when translating mRNA into proteins. Redundancy is exemplified by the fact that 61 of the 64 possible codons code for amino acids, with multiple codons often coding for the same amino acid.