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In some cases, a single amino acid substitution can cause a protein to lose its biological activity. In other cases, a single amino acid substitution causes no change to a protein's biological activity. Which statement can best be used as evidence to support an explanation for these observations

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Elin Hessel
Elin HesselLv2
28 Sep 2019
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Related questions

1.You are studying the world’s smallest enzyme which has the amino acid sequence of:

Met Ala Ser Met Tyr Ala Glu

You know that activity of this enzyme requires phosphorylation. You wish to design an inactive mutant form of this enzyme that can never be phosphorylated. You will use site-directed mutagenesis to alter the DNA sequence of this protein, resulting in a mutant protein.

Additional information: The most common resides to be phosphorylates are serine, threonine and tyrosine. In theory, these can be replaced with any other amino acid except for glutamic and aspartic acid, the shape and charge of a phosphorylated serine and aspartic acid are similar. Substitution with one of these amino acids would create a protein that looked like it was always phosphorylated (phosphomimic). Alanine is one of the most common substitutions, but others are possible and sometimes preferable to preserve other characteristics of the amino acid.

1. Write out the resulting amino acid sequence corresponding to your designed mutant protein here:

Identify amino acids which when being part of a protein structure have side chains that can participate in the hydrogen bond formation. Draw the structure of each amino acid and indicate how it can form the hydrogen bonding.

2. Identify amino acids which when being part of a protein structure have side chains that can participate in chemical reactions. Explain why and how. For instance which residues are used for post-translational modifications, for regulation of protein activity, how are glycans and lipids attached to proteins?

3. Identify amino acids which when being part of a protein structure have side chains that can ionize or are charged at pH 7. Based on the pKR values of the free amino acids estimate/calculate what percentage of the amino acid is in the charged form.

Explain why some amino acids, like serine in serine proteases, can ionize/lose proton at neutral pH while their pKR values suggest that this should not be possible.

1a. which is likely to be more deleterious, a 1bp deletion from an exon in the coding sequence of a gene, or a 3 bp deletion? Explain clearly what all the potential consequences of both deletions could be on the proteins amino acid sequence.

1b. how many different 9-nucleotide mRNA sequences could you make that would produce the peptide tyrosine-leucine-arginine? Assume you are using a cell-free system that does not require a START codon.

1c. imagine you have a single nucleotide substitution (an A has mutated to a G, for example) in an exon of a gene's coding region. It reduces the activity of that gene's protein in your cells to 50% of the usual level of activity. Imagine also that you have a single nucleotide substitution in the same gene's promoter region, and this mutation also reduces the activity of that gene's protein in your cells to 50% of the usual level of activity. Do the 2 mutations reduce the proteins activity level via the same mechanism? Explain your answer.

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