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Tutor profile: Sami H.

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Sami H.
Medical Student at the University of Colorado School of Medicine
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Questions

Subject: Chemistry

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Question:

What is Le Chatelier's principle? Describe it in terms of the following equilibrium equation assuming the concentration of CO2 were to increase. What might happen to the pH of the solution? CO2 + H2O <-> H2CO3 <-> H+ + HCO3-

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Sami H.
Answer:

Le Chatelier's principle is a topic in chemistry that is used to describe what happens to chemical reactions when an equilibrium reaction is perturbed be it with changes in concentrations, temperature, pressure. In terms of the chemical equation shown, if the concentration of carbon dioxide is increased in a closed system then the increased concentration will increase the rate of the forward reaction ultimately forming more H2CO3 to re-balance out the equilibrium. Over time, the equilibrium will re-establish and the forward and reverse rates will equal again. Because the concentration of H2CO3 increased, the concentration of H+ and HCO3- will also increase because the reactant in this part has increased. pH is a calculation based on the concentration of H+. The equation is pH = -log[H+]. If the concentration of H+ increased, then the pH decreases. So, in this example, increasing CO2 will decrease the pH because the concentration of the product H+ will increase.

Subject: Biomedical Science

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Question:

What is the purpose of insulin, how is it secreted, and how does it affect target cells?

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Sami H.
Answer:

Insulin is produced by the beta cells in the inslets of Langerhans in the pancreas. The pancreas is an endocrine and exocrine gland that sites posterior to the stomach in the abdominal cavity. When producing insulin the function of the pancreas is therefore acting as an endocrine gland because insulin will be used to signal to other cells in the body. Insulin is a protein that is initially produced as something called Pre-pro-insulin that is cleaved in multiple steps by enzymes to produce the final active insulin protein. The protein is then stored in vesicles in the beta cells and will await signalling to get exocytosed. Insulin is released in response to an elevated glucose level in the blood. The beta cells sense this by having increased production of ATP which inhibits the K+ channels which depolarizes the cells allowing the influx of Ca2+ which then allow the vesicles to fuse with the plasma membrane to exocytose the insulin into the blood. The insulin will then bind to cells such as liver cells. This will cause a cascade of events which causes the liver cells to increase the number of glucose transporters on the cell surface to increase the uptake of glucose into the cells for storage. The reason for all of this is to maintain a homeostasis of glucose concentration in the blood in a normal range, a process termed negative feedback.

Subject: Biology

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Question:

Describe the function of the sodium-potassium pump on cell membranes and its importance.

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Sami H.
Answer:

The sodium-potassium pump (Na+/K+ pump) is an ATPase transmembrane protein in the cell membranes of cells. This specialized pump is considered a primary active transport protein because it uses the energy of ATP to drive the movement of the elements Na+ and K+ against electrochemical gradients. The pump drives 3 sodium ions out of the cell and 2 potassium ions into the cell for each ATP hydrolysis reaction. The energy from ATP is required because these ions do not want to move in the direction indicated due to the concentration and electrical differences of the inside and outside of the cell. This transport protein therefore also establishes an electrochemical gradient since it drives the formation of chemical concentration gradients across the cell membrane as well as a charge difference since 3+ charges are leaving the cell and only 2 positives are entering for a net negative charge inside the cell. The charge separation now inside the cell as compared to outside can therefore be used to do work for other processes such as propagation of an electrical impulse down a neuronal axon to send signals.

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