If the sequence is changed from AGU to ACU, threonine would replace serine in the active binding site of the amino acid. Serine is the primary alcohol, while threonine is a secondary alcohol.
It would lose its proton more easily than the serine. If the catalytic activity of enzyme requires proton removal from serine by a particular substrate, threonine would lower the specificity of the enzyme as it would donate its proton rather easily.
If the sequence of mRNA (messenger ribonucleic acid) changes from AGU to GGU, glycine would replace serine in the active binding site of the enzyme. This would severely affect its function.
As glycine is a hydrophobic amino acid, while serine is an amino acid that is polar, replacement of serine with glycine would result in change in conformation of the protein receptor. It would result in disrupted functioning. Further, disturbing the chain of reactions it was carrying signal for.
If the sequence changes from AGU to AGC, nothing would happen as both codes for serine. If the sequence changes from GAA to GAU, glycine would replace the glutamic acid. Again, an amino acid that is non-polar would replace with an amino acid that is polar causing changes in the conformation, which would result in complete disruption of the receptor function.
GAA to AAA would replace the glutamic acid with lysine, and then the structure would be basic, as lysine is the basic amino acid. It would form proteins that are mutant. GAA to GUA would replace glutamate with valine, and then it would create a great disturbance in the structure of the chain as their structures are very different from each other. For example, sickle cell anemia disease is an example of this type.
If the sequence changes from UUU to UUC, no changes are observed as both codes for phenylalanine. If the sequence changes from UUU to UAU, the changes would be slight as tyrosine would replace phenylalanine and both are aromatic amino acids with relatable characteristic. The only difference is that tyrosine has a hydroxyl group that can interfere in the proteins action.
If the sequence changes from UUU to AUU, the changes would be in the conformation. Although both the amino acids are non-polar, if phenylalanine would be replaced by isoleucine, then there would be disturbance in the migration of the cells. It means there would be disturbance in the cellular functioning.