5. The protein known as tyrosinase is needed to make certain types of pigments.

Question

5. The protein known as tyrosinase is needed to make certain types of pigments. Tyrosinase is composed of a single polypeptide with 511 amino acids. Because each amino acid weighs 120 Da (average), the molecular mass of this protein is approximately 61,300 Da or 61.3 kDa People who carry two defective copies of the tyrosinase gene have the condition known as albinism. They are unable to make pigment in the skin, eyes and hair. Western blotting can be used to detect proteins that are translated from a particular mRNA. Skin samples were collected from a pigmented individual lane 1) and from three unrelated albino individuals (lanes 2, 3 and 4) and subjected to a Western blot analysis using an antibody that recognizes tyrosinase. Explain the possible cause of albinism in the three albino individuals 2 3 4 51 kDa

Explanation / Answer

The possible reasons could be:

Lane 2: Since the size of the polypeptide is reduced to 51kDa, it can be assumed that the process of translation is stopped in the middle meaning there could be a mutation in the patient that is nonsense in nature. Nonsense mutation are thos mutations in which a single codon that codes for an amisoacid is mutated to a chain terminating codon due to which the translation ends in the middle leaving an incomplete polypeptide.

Lane 3: Since there is no protein present in lane 3, this means the protein is alltogether absent. This can be caused by a mutation in a promoter region due to which polymerase is no longer able to bind and transcribe the desired mRNA so without any mRNA, protein would not be produced.

Lane 4: As seen in the gel, protein is present that too at an appropriate size. So this could only mean that the protein is not functional either due to a mutation at a site that us must for its activity of the protein has not folded the way it is supposed to be to be functional.

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