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Question
The given diagrams I and II represent the mechanism of action for two categories of hormones. Which of the following options correctly identifies the options A to H?
The given diagrams I and II represent the mechanism of action for two categories of hormones. Which of the following options correctly identifies the options A to H?
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Solution
The correct option is A A - Protein hormone, B - Receptor, C - Second Messenger, D - Steroid hormone, E - Receptor-hormone complex, F - Nucleus, G - mRNA, H - Protein
Diagram I and II represent the mechanism of action of a protein and steroid hormone respectively. In diagram I, A represents a protein hormone, B - a receptor and C - a second messenger. Protein hormones are hydrophilic and do not cross the plasma membrane. To overcome this problem, cells that are stimulated by such hormones have receptors present externally, nestled in their cell membrane called cell surface or plasma membrane receptors. So these hormones attach to their respective receptors. This causes a cascade of steps that result in the production of molecules called second messengers inside the cells.The job of second messengers is to convey the message from hormones or primary messengers to the inside of the cell. This is brought about by setting off another cascade of enzymatic reactions resulting in several physiological actions within the cell.
In diagram II, D represents a steroid hormone, E - hormone-receptor complex, F - nucleus, G - mRNA and H - protein.Steroid hormones are made of cholesterol, which means they are obviously lipophilic. Since the cell membranes are rich in lipids, these hormones have no problem moving across them and into the cell, they then attach to specific intracellular/intercellular receptors present in the nucleus. This hormone-receptor complex then moves to certain portions of DNA, specific to that complex. These stretches of DNA are called hormone responsive elements (HRE). Once they have bound to the HRE, they increase RNA transcription of that stretch of DNA resulting in the formation of mRNA and the corresponding protein, resulting in increased or decreased expression of the genes encoded for on that stretch.
Diagram I and II represent the mechanism of action of a protein and steroid hormone respectively. In diagram I, A represents a protein hormone, B - a receptor and C - a second messenger. Protein hormones are hydrophilic and do not cross the plasma membrane. To overcome this problem, cells that are stimulated by such hormones have receptors present externally, nestled in their cell membrane called cell surface or plasma membrane receptors. So these hormones attach to their respective receptors. This causes a cascade of steps that result in the production of molecules called second messengers inside the cells.The job of second messengers is to convey the message from hormones or primary messengers to the inside of the cell. This is brought about by setting off another cascade of enzymatic reactions resulting in several physiological actions within the cell.
In diagram II, D represents a steroid hormone, E - hormone-receptor complex, F - nucleus, G - mRNA and H - protein.Steroid hormones are made of cholesterol, which means they are obviously lipophilic. Since the cell membranes are rich in lipids, these hormones have no problem moving across them and into the cell, they then attach to specific intracellular/intercellular receptors present in the nucleus. This hormone-receptor complex then moves to certain portions of DNA, specific to that complex. These stretches of DNA are called hormone responsive elements (HRE). Once they have bound to the HRE, they increase RNA transcription of that stretch of DNA resulting in the formation of mRNA and the corresponding protein, resulting in increased or decreased expression of the genes encoded for on that stretch.
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