Question

PLEASE HELP

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).


(a) Describe the first interaction 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 researchers 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 that reached 100 percent at 10 minutes in Figure 1A , calculate the rate of decrease (percent decrease per minute) in the detected level of phosphorylated STAT5 from 10 to 30 minutes.


(d) The researchers claim that the similar regulation of carbohydrate metabolism by hepatocytes when the cells are treated with growth hormone or insulin results from the activation of different signaling pathways. Use the data from the researchers’ experiment to support their claim.

Answer 1

Answer a:

In the case of growth hormone, it activates the STAT5 signaling pathway. Therefore, initially, as the hepatocytes sense growth hormone, they imitate the STAT 5 pathway, which after some time maintains a steady rate.

In the addition of insulin, it activates Protein kinase B pathway initially.

Answer b:

The dependent variable in the experiment is the level of STAT 5 and protein kinase B proteins. Those proteins are depending upon the independent variables growth hormone and insulin. A negative control should be the addition of the same amount of water into hepatocytes, which will give no effect to the protein levels.

The researcher wants to identify short and long term effects of both hormones in terms of whether the signaling pathway interacts with each other or not and to identify the steady-state of the signaling pathway. That is why the researcher run the experiment for 240 minutes.

Answer c:

Insulin and protein kinase B interaction is the greatest and most prolonged response as is seen in the graph. Protein kinase B level reached to 100 after 30 minutes as insulin added while the level remained to near 80 even after 240 minutes.

The level of STAT 5 at the 10th minute = 100

The level of STAT 5 at 30th minute = 35

From 10 to 30 minutes, the level of STAT 5 = 100 – 35

From 10 to 30 minutes, the level of STAT 5 = 65

Duration = 30 – 10 minutes

Duration = 20 minutes

Rate of decrease = 65/20

Rate of decrease = 3.25 levels/min

Answer d:

The claim by the researcher is supported because of the known functions of insulin and growth factors. Both hormones have a tendency to respond to the presence of glucose. The growth hormone initiates STAT5 signaling for producing the Igf-1 factor that is important for utilizing glucose. The insulin hormone is well known for utilizing glucose.