1. What would you expect to happen to resident ER proteins that don’t display fu
ID: 133191 • Letter: 1
Question
1. What would you expect to happen to resident ER proteins that don’t display functional retrieval signals? Where would you expect these mutant ER proteins to eventually end up? Explain your answer.
2. Lysosomal hydrolases are transported from the trans Golgi network to late endosomes via the incorporation of M6P receptors into clathrin-coated transport vesicles. After delivery of the hydrolases, the receptors are returned to the trans Golgi. Describe what would happen to the hydrolases, their receptors and the function of cells under the following conditions. Explain your answers.
A. A mutation in the enzyme N-Acetyl-glucosamine (GlcNAc) phosphotransferase results in it being unable to recognize the signal patch on the surface of lysosomal hydrolases.
B. A mutation in the M6P receptor protein results in it being unable to bind to adaptor proteins of clathrin-coated vesicles.
C. The pH in late endosomes was raised to 7.0
D. The pH in the trans Golgi network was lowered to 6.0
3. What would be the consequences on vesicular traffic in cells with the following mutations? Explain your answers.
A. Mutation in a PIP kinase that renders the enzyme inactive.
B. Mutation in the Sar1 protein that makes it unable to bind GTP.
Explanation / Answer
1. The ER (endoplasmic reticulum) is responsible for protein systhesis and in case if the ER and has got any mutation so that it is unable to synthesize the desired protein, in this case the protein processing and modification plays a significant role and unwanted or undesired form of protein to be changed into useful manner with the help of Signal Sequence Cleavage method and N-Linked Glycosylation.
2. A. N-Acetyl-glucosamine (GlcNAc) phosphotransferase is responsible for the catalysis of asparagine residues? also known as mannose-6-phosphate or M6P. In case of mutation it wont catalyze the M6P hence no lysosomal activation.
B. M6P is key receptor to carry cell debris to the lysosomes. Hence mutation in M6P is unable to trasport clathrin-coated vesicles which usually carry the toxin coming from cell metabolism to the lysosomes.
C. The pH in endosomes is usually maintained between 5.5 pH to 4. In this pH the endosome will be stable and there will not be any proteolytic actvity. But increasing in pH may start proteolytic enzyme activity in side of endosomes.
D. The golgi network is sensitive to pH change and at lower pH there will be enough induction of H+ ions which may render the protein synthesis process and cellular transport mechanism.
3. A. The PIP kinase(1-phosphatidylinositol-4-phosphate 5-kinase?) enzyme is resposible to catalyze the metabolic pathways and signalling system. Hence the mutation in PIP kinase will not be sufficient to convert ATP to ADP which may be a reason behind enzyme inactivity.
B. The Sar1 protein is class of enzyme which is resposible for hydrolysis of GTP (guanosine triphosphate) and membrane trafficking?. The hydrolysis of GTP regulates the coat protein which is required for protein synthesis. Hence in case of mutation in Sar1 will not be able to hydrolyse the GTP due to unable to bind with surface of GTP.
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