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Azusa Pacific University Lysosomal Hydrolases Cell Biology Discussion

1. The principle pathway for transport of lysosomal hydrolases from the trans-Golgi network (pH 6.6) to the late endosomes (pH 6.0) and for recycling of Mannose-6-Phosphate (M6P) receptors back to the Golgi depends on the pH difference between those two compartments. From what you know about M6P-receptor binding and recycling pathways for delivery of material to lysosomes, describe the consequences of changing the pH in those two compartments.

a) What would happen if the pH in the late endosomes was raised to pH 6.6? complete the sentence by choosing one for bolded choices.

The M6P-receptor would (fail in/ succeed in) releasing its associated cargo and these proteins would be recycled back to the (Smooth ER/Trans-Golgi-compartment/rough ER). As a result, (“proteosomal”/ “endosomal”/ “lysosomal) proteins would fail to be delivered to the (“endosomal/lysosomal/ proteosomal)compartment and would accumulate in the (“TGN/Nucleus/Smooth ER.)

b) What would happen if the pH in the trans-Golgi network was lowered to pH 6.0?

Cargo proteins containing the M6P (“communication signal”/”termination signal”/ “sorting signal”) would (succeed/fail) in binding efficiently to the M6Preceptor protein. The result in this case would be that lysosomal (“kinases”/”oxidoreductases”/”isomerases”/”hydrolases) would be secreted by the default pathway.

2. You are studying a patient with familial hypercholesterolemia. After performing a biopsy to obtain liver cells. Using primers around the gene for the LDL receptor, you PCR this gene and sequence it. You find that it is the same as wild-type except for a point mutation changing a Tyr to a Phe. You also determine that the LDL binding site on the receptor is intact. Meanwhile, you witness a crime and are forced into the Witness Protection Agency. Before you go, what do you tell your assistant is your best guess as to the cause of your patient’s condition? fill-in the sentence by choosing of the bolded options

The mutated (“tyrosine”, “phenylalanine) esidue was probably a part of the YXX_ (where X is anything and _ is a [bulky hydrophobic] amino acid) in the (termination”, “cytosolic”, “vesicular”) domain of the LDL-R. This sequence interacts with the _2 subunit of the (“GGA1″, “AP181”, “AP2“) assembly particle and is responsible for clathrin-mediated internalization of the LDL-R bound to LDL.

3.In polarized MDCK cells, proteins X and Y normally are located to the apical plasma membrane domain, and are not observed to any significant degree in the basolateral membranes of these cells. To investigate the manner in which these two proteins arrive at this subcellular localization you transform these cells with a plasmid containing a dominant-negative form of one of the proteins of the AP-2 adaptor protein complex and observe the subsequent distribution of proteins X and Y. After treatment, protein X remains at the apical membrane, but protein Y now is primarily observed in the basolateral membranes. Explain how expression of a dominant-negative AP-2 complex can affect the subcellular distribution of protein Y but not protein X?


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