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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). (AKA QUESTION THAT IS NOT BAR GRAPH)
Figure 1. The level of phosphorylated signaling proteins STAT5 (A) and protein kinase B (B) in cells cultured in the presence of growth hormone or insulin
(a) Describe the first interaction that triggers signaling to begin in a target cell.
A ligand/hormone, binds to a receptor protein 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.
(AKA QUESTION THAT IS NOT BAR GRAPH)
The response indicates that a dependent variable is the level of phosphorylated signaling protein. The response indicates that a negative control for the effects of hormone addition is the zero time point when hormone is added. The response indicates that the response to the hormone might take some time to start.
(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.
(AKA QUESTION THAT IS NOT BAR GRAPH)
The addition of insulin caused a high level of phosphorylated protein kinase B to the end of the experiment. The rate of decrease is 3.25% per min.
(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.
The response indicates that the data show that different signaling proteins are phosphorylated by the two different hormones, which supports the researchers' claim.
Scientists used cells called fibroblasts to study factors that cause nondividing cells in the G0 stage of the cell cycle to reenter the cell cycle and undergo mitosis. In a laboratory, fibroblasts typically grow and divide when they are cultured in a growth medium that contains 10% serum (the liquid part of blood that remains after blood clots). If fibroblasts are cultured for 48 hours in the absence of serum (serum-starvation), they stop dividing and enter the G0 stage of the cell cycle.The scientists divided serum-starved fibroblasts into groups to which they added no serum, 10% serum, or 0.1% serum. Each of the groups with 0.1% serum was also treated to block the production of only one or combinations of four proteins (p16, p18, p21, and p27) that are inhibitors of cyclin-dependent kinases. The scientists grew the fibroblasts for 48 hours and then measured the amount of DNA replication taking place to determine wh
The response indicates that group 3 in which p16 is blocked does not appear to play a role in blocking cell cycle entry.
(b) Based on the data for the groups of cells cultured with 0.1% serum (groups 3 to 7), identify the groups(s) most likely to include cells undergoing mitosis.
(AKA QUESTION WITH BAR GRAPH)
The response indicates that cells undergoing mitosis are most likely to be found in group 7 OR in groups 4, 5, 6, and 7.
(c) Neurons (nerve cells) of the central nervous system (brain and spinal cord) are in G0 of the cell cycle and generally do not divide in response to an injury. The scientists predict that they can use the data from this experiment to help them treat individuals who suffer from spinal cord injuries. Provide reasoning to support the scientists' prediction.
(AKA QUESTION WITH BAR GRAPH)
The response indicates that blocking cyclin-dependent kinase inhibitors made fibroblasts divide. Successfully blocking this can make neurons reenter the cell cycle and divide.
(d) Interactions between cyclins and cyclin-dependent kinases control the cell cycle. Explain how the presence or absence of inhibitors of cyclin-dependent kinases might play a role in normal cells becoming cancer cells.
Lack of the appropriate cyclin-dependent kinase inhibitors might let cyclin-dependent kinases continue to form. That will result in almost continuous cell cycling with DNA replication and cell division.
