ECS 1501 ASSIGNMENT 6 QUESTIONS AND 100% CORRECT ANSWERS

ECS1501 ASSIGNMENT 6 WITH 100% CORRECT ANSWER After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify the RNAs attached to it. Which of the following proteins do you expect the RNA from the rough endoplasmic reticulum to encode? a. soluble secreted proteins b. ER membrane proteins c. plasma membrane proteins d. all of the above - CORRECT ANSWER===D The rough ER consists of ER membranes and polyribosomes that are in the process of translating and translocating proteins into the ER membrane and lumen. Thus, all proteins that end up in the lysosome, Golgi apparatus, or plasma membrane, or are secreted, will be encoded by the RNAs associated with the rough ER. Cells have oligosacchari des displayed on their cell surface that are important for cell - cell recognition. Your friend discovered a transmembrane glycoprotein, GP1, on a pathogenic yeast cell that is recognized by human immune cells. He decides to purify large amounts of GP1 by expressing it in bacteria. To his purified protein he then adds a branched 14 -sugar oligosaccharide to the asparagine of the only Asn -X-Ser sequence found on GP1 (Figure Q15 -48). Unfortunately, immune cells do not seem to recognize this synthesized glycoprotein. Which of the following statements is a likely explanation for this problem? a. The oligosaccharide needs to be further modified before it is mature. b. The oligosaccharide should have been added one sugar at a time. c. The oligosaccharide needs a disulfide bond. d. The oligosaccharide should have been added to the serine instead of the asparagine. - CORRECT ANSWER===A Oligosaccharides are usually further modified by enzymes in the ER and the Golgi before the glycoprotein is inserted into the plasma membrane. The other choices are untrue, and thus are not good explanations. Oligosaccharides are added to the Asn and not the Ser [choice (a)] and are added as a branched 14 -sugar oligosaccharide [choice (b)]. Disulfide bonding occurs between cysteines of proteins and not in sugars [choice (d)]. Figure Q15 -34 shows the organization of a protein that normally resides in the plasma membrane. The boxes labeled 1 and 2 represent membrane -spanning sequences and the arrow represents a site of action of signal peptidase. Given this diagram, which of the following statements must be true?