Describe how each of the following mutations will affect protein B’s activity. A

Question

Describe how each of the following mutations will affect protein B’s activity.

A deletion mutation in the gene B promoter that causes increased transcription of gene B.

A silent mutation in the gene B protein coding sequence.

A missense mutation in the gene B protein coding sequence.

A 2-bp insertion after the 3rd base pair in the gene B protein coding sequence.

Deletion of base pair numbers 256, 257 and 258 in the gene B protein coding sequence. (Note: The entire coding sequence is 303 base pairs, including the start codon and the stop codon.)

Explanation / Answer

A deletion mutation in the gene B promoter that causes increased transcription of gene B will not affect the proteins activity; it will only change the concentration of the protein in the cell.

A silent mutation in the gene B protein coding sequence will have no effect on the protein's activity because silent mutations do not change the amino-acid sequence of proteins.

A missense mutation in the gene B protein coding sequence can have no to severe effects on the protein's activity, depending on the site and nature of the mutation. If the substituted amino-acid is similar to the native amino-acid and does not involve the active site of the protein, very little or no effect may be seen. If the substituted amino-acid is different from the native amino-acid and involves the active site of the protein, severe effects may be seen and the activity may be completely lost.

A 2-bp insertion after the 3rd base pair in the gene B protein coding sequence will change the reading frame, and will likely result in premature termination. Protein B will not be produced at all.

Deletion of base pair numbers 256, 257 and 258 in the gene B protein coding sequence means deletion of the 86th codon (85th amino acid). Such mutations are usually very deleterious and the protein is likely to be non-functional. Rarely, the protein may retain its functionality.

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