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Unformatted text preview: Biological Sciences 54 Spring 2006 Problem Set 4 Answer key 1. A) 2 pts. The human IDA gene must be on chromosome 4. This is the only human chromosome found in all the hybrids that exhibit no lysosomal accumulation. This means that the presence of human chromosome 4 provides the hybrid with IDA, which is targeted to lysosomes where it can break down macromolecules, effectively rescuing the mutant mouse cells. B) 3 pts. The fact that the mutant mouse cells can survive by taking up IDA from the medium implies that their M6P-receptor mediated scavenger pathway is functional. Since co-culturing failed to rescue the mutant mouse cells, the lysosomal enzymes secreted by the I-cells cannot bind M6P-receptor and be endocytosed. Since the mouse cells do not secrete normal IDA, the I-cells cannot endocytose functional enzymes either. When the two cell types are fused, their differing genetic defects allow complementation the mouse cells provide the enzyme required for the mannose 6-phosphate modification of IDA, and the I-...
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This note was uploaded on 04/07/2008 for the course MCB 54 taught by Professor Lue during the Fall '06 term at Harvard.
- Fall '06
- cell biology