Solved by a verified expert:Because the genetic code is a universal code in biology, in general the nucleotide sequence of important genes is highly conserved across many different species of organisms. It is very common for 70% or more of the nucleotides in a gene to be conserved among very different organisms. Redundancy in the genetic code allows for small differences in the nucleotide sequence for a given gene without significant variations in the amino acid sequence of a protein. For example, the nucleotide sequence of the gene for insulin, the peptide hormone required for glucose uptake by many body cells, is well conserved (greater than 80% similarity) in many vertebrate species. As a result of this conservation of nucleotide sequence, comparing the peptide sequence for insulin from cows, humans, sheep, dogs, and rats often shows fewer than six or seven differences in amino acid sequence. However, point mutations in certain positions of a codon can create changes that dramatically alter the protein produced. Examples of mutations of this type include frameshift mutations. To help you understand why the nucleotide sequences for important genes are highly conserved, work together in a group of four or five students to complete the following assignment. Imagine that you have just purified a new protein from the brain of adolescent males that you believe may be responsible for excessive hair-combing behavior. From peptide-sequencing experiments, you have determined that this protein contains the following peptide sequence: Trp-Met-Asp-Gly-Trp-Met. Determining the nucleotide sequence of mRNA that was used to translate this part of the protein will enable you to identify the chromosomal location of this new gene and allow you to isolate and clone this gene. It is known that this peptide sequence is highly conserved among males that demonstrate excessive hair-combing behavior which suggests that this portion of the protein is important for its functions. In addition, a mutant form of this protein has also been discovered that appears to result in the loss of the excessive hair-combing behavior. This mutant sequence arises from a single point mutation in the nucleotide sequence of the normal (wild-type) gene for this protein that creates a frameshift mutation. The peptide sequence from this mutant protein is Met-Tyr-Val-Cys-Met- Tyr. Use TranslationLab to complete the following exercises. Determine the sequence of a mRNA that could be used to translate this peptide. Can you determine another sequence of mRNA that would also code for this peptide? Why or why not? Explain your results. Once you have deciphered the mRNA sequence for the normal protein, introduce changes in this sequence until you have determined the nucleotide sequence that specifies the mutated peptide sequence. Examine this mRNA sequence and identify the codon or codon(s) that were altered to create the mutant peptide.
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