Questions related to Signal Transduction and transcytosis

Question 11 What is transytosis? A. Transcytosis is the mechanism where apically destined destined endocytosed proteins are sorted into a class of transport vehicles that move across the cell and fuse with the apical membrane. E.g. this process helps in movement of extracellular material from one side of epithelial cell to another. Question 12 You are performing an experiment to determine if your protein of interest can enter the nucleus via active transport involving Ran. What kind of molecule is Ran? A. Ran is a GTPase molecule. In the cytosol, Ran is bound to what nucleotide? A. Guanosine Your protein of interest will bind to a nuclear transport receptor through what mechanism? A. By Active Transport through nuclear pore through Ribonucleo proteins (RNP). What exactly is the role of Ran in nuclear import? A. Ran, a small GTPase exists in two conformations, one complexed with GTP and other with GDP. Ran forms trimolecular cargo complex with Exportin I protein, NES (RNP Nuclear Export signal ). Interaction of cargo complex with proteins in nuclear pore leads to movement of cargo complex through pore. Question 13 True or false and justify your answer: There is no fundamental difference between signaling molecules that bind to cell-surface receptors and those that bind to intracellular receptors. False Cell-surface receptors are intergral transmembrane proteins controlling cascade reactions while intracellular receptors are soluble proteins localized within the nuceloplasm or cytoplasm. The typical ligands for nuclear receptors are lipophillic as steroid hormones which directly interact with DNA. Question 14 N-linked oligosaccharides are initially added to proteins where in the cell? O-linked oligosaccharides are initially added to proteins where in the cell? Is this an example of an N-linked oligosaccharide, an O-linked oligosaccharide, both or neither A.Most plasma membrane and secretory proteins contain one or more carbohydrate chains through glycosylation. These reactions occur in lumen of ER. This is O-linked oligosaccharide as it has only N-Acetylgalactosamine visible with serine amino acid wheras N-linked oligosaccharides have N-acetylglucosamine linked to mannose and sialic acid. Question 15 If you attach the gene for protein disulfide isomerase to the gene for insulin and then express this recombinant protein in a cell, where would you expect the insulin to end up and why? A. In Lumen of RER . As this contain KDEL (another example is molecular chaperones). If there was no COP1 available would this have an impact on where in the cell the recombinant insulin ended up Probably since there’s no retrograde transport it would probably keep moving forward in the secretory pathway (affinity of KDEL sequence in different compartments not known) The KDEL receptor is a Golgi/intermediate compartment-located integral membrane protein that carries out the retrieval of escaped ER proteins bearing a C-terminal KDEL sequence (Lys-Asp-Glu-Leu). This occurs throughout retrograde traffic mediated by COPI-coated transport carriers. The name "COPI" refers to the specific coat protein complex that initiates the budding process on the cis-Golgi membrane. The coat consists of large protein subcomplexes that are made of seven different protein subunits.