Question

Researchers compared the amino acid sequences of the transport protein in zebra fish, puffer fish, mice, and humans. They found many stretches with identical sequences in all four species. Does this mean that the corresponding mRNA base sequences are also the same in these four species? Explain why or why not.

Short answer

The identical amino acid sequences of the transport protein in zebra fish, puffer fish, mice, and humans do not necessarily mean that the corresponding mRNA base sequences are the same in these four species. This is due to codon degeneracy in the genetic code, where multiple mRNA codons can code for the same amino acid, allowing for different mRNA sequences to produce the same protein.

Step-by-step solution

The genetic code is the set of rules that translates nucleotide sequences in mRNA into amino acid sequences in proteins. It consists of 64 codons, which are triplets of nucleotide bases (A, C, U, and G), corresponding to the 20 amino acids and 3 stop codons. This code is nearly universal among living organisms. #Step 2: Discussing codon degeneracy#

Due to the nature of the genetic code, there are instances in which redundancy exists, meaning that multiple different codons code for the same amino acid. This is known as codon degeneracy or redundancy. For example, the amino acid leucine can be encoded by six different codons: UUA, UUG, CUU, CUC, CUA, and CUG. Thus, it is possible for two organisms to have the same amino acid sequence in a protein even though their mRNA base sequences differ. #Step 3: Relating amino acid sequences to mRNA sequences#

Since amino acids are encoded by codons in mRNA, an identical amino acid sequence found in the transport protein of the four species means that each species has an mRNA sequence that codes for the same amino acid chain. However, due to codon degeneracy, this does not mean that the mRNA sequences in the four species are necessarily the same. #Step 4: Concluding the explanation#

In conclusion, even though the amino acid sequences of the transport protein are identical in zebra fish, puffer fish, mice, and humans, it does not necessarily mean that the corresponding mRNA base sequences are the same in these four species. This is due to the fact that multiple mRNA codons can code for the same amino acid, allowing for different mRNA sequences to produce the same protein.

Key concepts

Codon Degeneracy

When we talk about codon degeneracy, we're delving into one of the most fascinating aspects of genetic code which beautifully demonstrates nature's efficiency. Codon degeneracy refers to the genetic code's feature where a single amino acid can be coded by more than one codon — a triplet of nucleotides. For instance, if you've encountered the amino acid arginine, you might be surprised to find it's specified by six different codons!

Think about codon degeneracy as nature's own way of buffering against errors during DNA replication. Because multiple codons encode a single amino acid, small mutations that might change one nucleotide could still result in the same amino acid, and thus the protein's function remains unchanged. This redundancy is elegant because it contributes to the robustness of living organisms, allowing them to withstand genetic mutations that would otherwise be harmful.

mRNA Base Sequences

The mRNA base sequences are essentially the vital instructions for assembling amino acids into proteins. During the transcription phase of protein synthesis, an enzyme reads DNA and creates a complementary strand of mRNA. This mRNA is then organized into codons, groups of three bases each, which match up to amino acids. However, it's important to note that the genetic code is universal — meaning the codons are interpreted in the same way across nearly all species.

Why Identical Proteins Don't Mean Identical mRNA

But here's the kicker: just because a series of amino acids matches up across species, doesn't mean the mRNA sequences will be identical because of codon degeneracy. This redundancy in the genetic code allows for variability in the genetic sequence without affecting the protein's sequence. It's quite a clever system!

Amino Acid Sequences in Proteins

Focusing on amino acid sequences in proteins is key to understanding how the 'words' of mRNA translate into the 'sentences' of proteins. Each amino acid added to a growing protein chain influences the structure and function of that protein. The order is critical — just like in a sentence, a change in the order can shift the entire meaning, or in this case, the function of the protein.

Proteins with the same amino acid sequences across different species point to evolutionary conservation, as is the case with the transport proteins in zebra fish, puffer fish, mice, and humans. Yet, these proteins' similarities in amino acid sequences don’t strictly dictate that the mRNA sequences will also be identical, thanks to the magic of codon degeneracy. This allows nature to favor certain protein structures while still allowing a range of genetic variations.