03-11-2008, 12:45 PM
The answer is: D
Collagen peptides assemble into helical tertiary structures that form quaternary triple helices. The triple helices in turn assemble end to end to form collagen fibrils that are essential for connective tissue strength. Over 15 types of collagen contribute to the connective tissue of various organs, including the contribution of type I collagen to eyes, bones, and skin. The fact that only one of two 2 alleles is normal in this case implies that a mutant 2 allele could be responsible for the disease (even if the 2 locus is on the X chromosome, since the baby is female with two X chromosomes). The mutant 2 collagen peptide would be incorporated into half of the type I collagen triple helices, causing a 50% reduction in normal type I collagen. (A mutant 1 collagen peptide would distort 75% of the molecules since two 1 peptides go into each triple helix.) The ability of one abnormal collagen peptide allele to alter triple-helix structure with subsequent degradation is well documented and colorfully named protein suicide or, more properly, a dominant-negative mutation
Collagen peptides assemble into helical tertiary structures that form quaternary triple helices. The triple helices in turn assemble end to end to form collagen fibrils that are essential for connective tissue strength. Over 15 types of collagen contribute to the connective tissue of various organs, including the contribution of type I collagen to eyes, bones, and skin. The fact that only one of two 2 alleles is normal in this case implies that a mutant 2 allele could be responsible for the disease (even if the 2 locus is on the X chromosome, since the baby is female with two X chromosomes). The mutant 2 collagen peptide would be incorporated into half of the type I collagen triple helices, causing a 50% reduction in normal type I collagen. (A mutant 1 collagen peptide would distort 75% of the molecules since two 1 peptides go into each triple helix.) The ability of one abnormal collagen peptide allele to alter triple-helix structure with subsequent degradation is well documented and colorfully named protein suicide or, more properly, a dominant-negative mutation