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 phosphorylation STAT5 response that reached 100 percent at 10 minuted 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.

Ligand-receptor interaction is the first interaction that triggers cell signalling.

Ligands are the hormones, drugs or neurotransmitters that specifically bind with receptors present in cell surface to initiate cell signalling. Ligand binding to the receptor is reversible. Binding of the ligand to the receptor can activate or inactivate receptor. Activation may lead to cell signalling pathways. Inside cells, there are secondary molecules which on activation starts a cascade of reactions. which in-turn regulate the function of the ligand molecule.

At first, the activated receptor relates with G proteins molecules in the cell.

before the ultimate physiological effect of the ligand on the cell's behavior is produced Therefore, the cellular signaling starts as soon as the first messenger (the ligand) binds to its receptor.

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