A) Describe the first interatcion that triggers signaling to begin in a target cell.

B) Identify a dependent variable in the experimental design. Identify a negative control for the effects of hormone addition. Identify a likely reason why the researchs continued their experiment for 240 minutes.

C) Describe the hormone and signaling protein combination that produced the greatest and most prolonged response. For the phosphorylated STAT5 response the reached 100 percent at 10 minutes in figure 1A, calculate the ragte of decrease (percent decrease per minute) in the detected level of phosphorylated STAT5 from 10 to 30

D) The researchers claim that the similar regulation of carbohydrate metabolism by hepatocytes when the cells are treated with growht hormone or insulin results from the activation of differnt signaling pathwaysl Use the data from the researchers experiment to support ther claim.

Growth hormone and insulin are protein hormones that regulate carbohydrate metabolism by hepatocytes (liver cells) through the activation of intracellular signaling pathways. Researchers investigated whether the two hormones trigger the same or different intracellular signaling pathways in hepatocytes. The researchers added either growth hormone or insulin to parallel cultures of hepatocytes. At several time points after the hormone addition, they purified total intracellular protein from the cells and quantified the level of the phosphorylated forms of two proteins involved in two different signaling pathways (Figure 1. A and B).

30 00 240 Time After Hormone Addition (min) 60 Time After Hormone Addition (min) 30 240 --Growth Hormone Insulin Level of Phosphorylated STAT5 (relative to maximum) Level of Phosphorylated Protein Kinase B (relative to maximum)