Mutations in the genes encoding collagens often have detrimental consequences, r

Question

Mutations in the genes encoding collagens often have detrimental consequences, resulting in severely crippling diseases. Particularly devastating are mutations that change glycines, which are required at every third position in the collagen polypeptide chain so that it can assemble into the characteristic triple-helical rod (see figure below). a. Would you expect collagen mutations to be detrimental if only one of the two copies of a collagen gene is defective? b. A puzzling observation is that the change of a glycine residue into another amino acid is most detrimental if it occurs toward the amino terminus of the rod-forming domain. Suggest an explanation for this.

Explanation / Answer

a. Yes, they are detrimental since collagen mutations are dominant in nature. Three collagen chains form a triple helical rod. The defective genes interfere with the formation of a triple helical rod.

b. The assembly of collagen monomers into triple helical rod begins from the amino terminal ends. Hence, mutation at this terminus is detrimental as it severely disrupts normal rod formation.

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