Question

I need help with 6 a and b please. can you explain how you got the answers?

State rational for your answer: 6) In unstimulated muscle cells, the glucose transporter Glut4 is present in the membrane of endosomes. Upon stimulation of these cells with insulin, the endosomes fuse with the plasma membrane, thereby depositing Glut4 in the plasma membrane, where it serves to transport glucose into the cells. In order for insulin to elicit this change in Glut4 localization, insulin must bind to its receptor, present in the plasma membrane of some cells. To determine if a stem cell line can be induced in culture to differentiate into muscle cells in which Glut4 is expressed and exhibits this insulin-dependent change in behavior, the following studies were undertaken. A stem cell line was incubated under culture conditions in which stem cells can differentiate into various specific cell types. The cells were then incubated in the presence and absence of insulin. To determine if either Glut4 or the insulin receptor were present on the cell surface of cells within this population, antibodies that specifically recognize each protein were used to label the cells. Glut4 on the cell surface was detected by an anti-Glut4 antibody, which fluoresces green; the insulin receptor on the cell surface was detected by an anti-insulin receptor antibody, which fluoresces red. These cells were then placed in a fluorescence activated cell sorter FACS machine and sorted based on both red and green fluorescence. The following data were obtained. Each • on the graphs represents 20 cells. An increased value of fluorescence intensity indicates that more antibody has bound to those cells (12). (a) - Insulin (b) + Insulin Green fluorescence TTITIT Green fluorescence → 100 107 104 107 104 Red fluorescence → 100 Red fluorescence O a) Do all cells in the population express insulin receptor on their surface? Is this expression dependent on the presence of insulin? Explain b) Do any cells in the population express Glut on their surface? Is this expression dependent on the presence of insulin receptor? Is this expression dependent on the presence of insulin? Explain.

Answer 1

a)

All cells do not express Insulin Receptors on their surface. In the given data, the lower left quadrant in Figure (a) shows cells that do not express the Insulin receptor (Red Fluorescence Intensity 10⁰ --> 10⁴). The expression of Insulin Receptors is not dependent on the presence of Insulin since the lower right quadrant in Figure (a) has cells that have the Insulin receptor (Red Fluorescence), in the absence of Insulin.

b)

Some cells do express GLUT 4 (Upper right quadrant in Figure (b)) and this expression is dependent on the Presence of insulin receptor, since cells that do not express the insulin receptor, also do not express GLUT4 (cells in lower left quadrant of Figure (b)).

This expression is also dependent on the PResence of Insulin as cells do not show any GLUT 4 expression in the absence of Insulin (Figure (a)), while some cells do express GLUT4 in the presence of Insulin (Figure (b)).