Fundamental Macromolecules and Concepts - Biochemistry

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 .

Normal blood pH is 7.4. A decrease in pH could indicate acidosis, which is associated with too much in the blood. Respiratory acidosis occurs as the result of the lungs failing to eliminate enough .

Here is the equation needed to find the correct answer to this question.

Less carbon dioxide in the lungs from the constant exhalation will cause the decrease in the hydrogen ion concentration in the blood, resulting in a rise in pH.

The pH of plasma is regulated by the following equilibria:

According to Le Chatlier's Principle, when the concentration of protons increases (plasma becomes acidic) the equilibrium shift will be to the left of the equation. Therefore, there will be an initial increase of carbon dioxide. However, the body needs to rid itself of the excess carbon dioxide. This happens via hyperventilation - the increased breathing out of carbon dioxide.

The spontaneity of a reaction says nothing about the reaction's speed. For a spontaneous reaction, the change in Gibbs free energy is negative. In other words, the products have lower energy than the reactants. With low temperatures and negative enthalpy, a reaction can still proceed spontaneously if entropy decreases.

The Gibbs Free Energy ()of a reaction tells us whether or not the reaction is favorable. A favorable reaction is also known as spontaneous, and has a negative . A non-favorable reaction is non-spontaneous, and has a positive . The term exergonic (meaning energy exits the system) is also used for a reaction with a negative , while the term endergonic (meaning energy enters the system) is used for a reaction with a positive . Therefore, a reaction with is both exergonic and spontaneous.