pH Regulation - Biochemistry

Diabetic ketoacidosis is a condition that can occur in people who have diabetes. In this situation, there is a deficiency in insulin production. Consequently, the glucose that is present in the blood has no way of entering cells. These cells, in turn, become starved for energy, causing the body to burn fat and produce acidic ketone bodies as an alternative energy source. The energy deficit that cells experience as a result of not having access to glucose causes significant production of these acidic ketone bodies. In fact, so many of these ketone bodies are produced that it overwhelms the body's normal pH buffering capacity, and thus the blood can become dangerously acidic. High levels of intracellular glucose is incorrect because the lack of insulin causes glucose to be unable to enter these cells. Gluconeogenesis in the liver is also increased because the energy starved cells alert the body that they need energy. The body is "tricked" into "thinking" that the cells aren't getting energy due to a shortage of glucose, even though plenty of glucose is actually available. Thus, gluconeogenesis exacerbates the high blood glucose levels. Fat breakdown in the body is also increased. It is this breakdown of fat that provides the ketone bodies as an alternative fuel source for the body. Glucagon output is also increased because, as explained above, the body "thinks" it is energy starved due to there not being enough glucose even though there is plenty. This hormone increases gluconeogenesis and fat breakdown, as described above.

Thus the ratio of is equal to , or the ratio of is equal to

The best buffering capacity occurs when pH = pKa. When this is true, the ratio of ionized to unionized form of the buffer is 1:1. Thus the solution can best resist changes in pH, as hydrogen ions can be quenched or donated to solution to resist change. Acetic acid would have almost the same buffering capacity since its pKa is almost as close to 4.0 as that of formic acid.

Low blood pH suggests that the patient has high concentration of hydrogen ions. To solve this question, we need to look at the following reaction, which represents the major blood buffer system:

One way the body controls the amount of hydrogen ions in the blood is by altering the amount of carbon dioxide. Recall that, according to Le Chatelier’s principle, increasing carbon dioxide will push the reaction the right and increase hydrogen ion concentration whereas decreasing carbon dioxide will decrease hydrogen ion concentration.

Body controls carbon dioxide levels via breathing. Hyperventilation refers to increased breathing whereas hypoventilation refers to decreased breathing. During hyperventilation the person breathes out excess carbon dioxide (decreasing the hydrogen ion concentration). During hypoventilation, on the other hand, a person breathes slowly and retains carbon dioxide (increasing the hydrogen ion concentration). The patient in this question has low blood pH (high hydrogen ion concentration); therefore, of the options, the patient must be hypoventilating.

A buffer system occurs when equal amounts of a weak acid and its conjugate base (or vice versa) is added together. Maintaining blood pH is a very important aspect in maintaining homeostasis. The body does this utilizing the carbonic acid/bicarbonate buffer system. The concentrations of the base and acid are altered accordingly to maintain a constant blood pH.

Hydrochloric acid is found in the stomach to maintain an acidic pH, phosphoric acid does play a role in buffering the blood, but is not the major buffer. Acetic acid is found in vinegar and does not play a major role in regulating blood pH.

Blood pH is maintained via the lungs and the kidneys. Lungs alter the amount of carbon dioxide expelled to maintain blood pH. Consider the reaction below.

Carbon dioxide is decreased when pH is low (high hydrogen ion concentration). Decreasing carbon dioxide will shift the reaction to the left and decrease the hydrogen ion concentration. Similarly, the body compensates for high blood pH by increasing carbon dioxide.

Kidneys alter blood pH by increasing or decreasing the excretion of bicarbonate ions. Using the reaction above, we can determine that increasing bicarbonate ion in blood will decrease hydrogen ion concentration whereas decreasing bicarbonate ion will increase hydrogen ion concentration. To combat high blood pH (low hydrogen ion concentration), the bicarbonate ion needs to increased in the blood. The kidneys do this by decreasing the excretion of the bicarbonate ions.

pH is calculated via the following equation:

refers to the concentration of hydrogen ions in the solution, which in this case is the same as the concentration of the acid since hydrochloric acid is a strong acid and will fully dissociate in solution. Thus, we have:

Buffering capacity refers to how well a buffer works. A buffer is a substance that maintains a specific pH regardless of added acid or base. Thus, buffering capacity refers to how well a buffer maintains the pH of a solution despite the the effects of added acid or base. The other choices do not apply to this definition.

Recall the equation for pH. Here is the calculation that should be performed:

Our main blood buffer system works to protect against large pH changes in the blood. This system relates bicarbonate, carbonic acid, and carbon dioxide via the following equilibria:

While the phosphate buffer system is an important biological buffer, it is not the main buffer system in human blood.

Here are the equations we need to use to find the pOH of our solution of sulfuric acid:

Carbon dioxide concentration is low in the blood surrounding the lungs and high in those around muscle, relatively speaking, because cell respiration by the muscles produces carbon dioxide. Therefore, hemoglobin binds oxygen quite well at the lungs, as it should in order for us to be able to breathe, and then binds it much less effectively around the muscles. This allows the oxygen to unbind and enter the muscle tissue (this process is facilitated by myoglobin) where it is used by the actively respiring muscle cells.

Carbonic anhydrase in red blood cells catalyzes the following equilibrium reaction:

The carbonic acid formed then naturally gives up a proton to form . This is why elevated levels lower the blood pH. When more is removed through more rapid breathing, this shifts the equilibrium reaction back to the left (Le Chatelier's principle), prompting more and to turn into which then turns into and . Thus, carbonic anhydrase now catalyzes the reaction toward the left in this scenario, raising the pH. is neither an acidic nor basic molecule by itself (and if it were basic then ridding of it would actually lower the pH further), and while the answer involving oxygen may be tempting, oxygen is not found dissolved in blood plasma; it is bound to hemoglobin, and thus it does not bind protons in the blood to form water.

In this question, we're told that a buffer solution consisting of carbonic acid and bicarbonate needs to be prepared. The solution needs to have a concentration of , a volume of , and a pH of .

First, we need to recognize that in order to solve this problem, we'll need to utilize the Henderson-Hasselbalch equation.

The acid in the above expression will be carbonic acid, and its conjugate base is bicarbonate. We can plug in the values we have for pH and pKa to obtain the ratio of base to acid.

Now that we have the ratio of base to acid, we can figure out what fraction of our solution will be base, and what fraction of it will be acid. To find this fraction, we have to realize that for every moles of base, there is mole of acid. Thus, there are a total of moles of acid and base.

Next, we need to take into account the volume and molarity that we want in our desired solution in order to find the total number of moles for our final solution.

Equipped with knowing how many total moles we want in our desired solution, in addition to the portion of our solution that is acid and the portion that is base, we can at last calculate how many moles each of carbonic acid and bicarbonate we need in our solution.

Carbonic acid:

Bicarbonate:

Using the Henderson Hasselbach equation:

Thus, the ratio of acid to base =

This question requires you to use the Henderson-Hasselbach equation, one of the most important equations in biochemistry. The equation is:

where is the concentration of the conjugate base, and is the concentration of the acid. In this scenario, is the conjugate base, while is the acid. With the numbers given in this question, the equation should look like this:

Here is the equation used to find the correct answer:

Water, , is an amphoteric substance--it can act as either an acid or a base. In certain circumstances, water can act as a Bronsted-Lowry acid by donating a proton.

As seen above, donated one of its hydrogen atoms, becoming .

In other cases, water can act as a Bronsted-Lowry base by accepting a proton.

As seen above, accepted a hydrogen atom to become .

Therefore, water can act as either an acid or a base depending on the situation. There are other amphoteric substances, but water is definitely the most common.

Here is the equation that you need to find the answer.

Thus, the pH of this solution is closest to .