Biological Buffers

Core Concepts – Biological Buffers

In this article, you will be able to describe what a buffer is, why buffers are important, and how specific buffers have biological significance in mammalian systems.

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Buffer Systems and their Significance

A buffer is a system which maintains a constant pH. However, different types of buffers exist. Some buffers may be acidic, while others may be basic. This difference in acidity or basicity is explained through their component parts.

Types of buffers - acidic and basic
A table of biological buffers are shown above.

An acidic buffer contains a weak acid (HA) and a conjugate base (A-). A basic buffer contains a weak base (B) and a conjugate acid (BH+). A sample of weak acids and their conjugate bases are shown below.

Acidic Buffer examples
A few examples of acidic buffers are shown above.

A buffer solution may be created in the laboratory. For instance, an undergraduate student may create a buffer solution through dissolving a weak acid (HA) and its conjugate base (A-) in a 500. mL beaker. However, buffers are not limited to the laboratory. Buffers play an immense role in biological systems where maintaining constant internal conditions, otherwise known as homeostasis, is critical for survival. And pH is no exception. There are two classes of buffers which play crucial roles in the human body: (1) the bicarbonate buffer system and (2) the phosphate buffer.

The Bicarbonate Buffer System

Let’s imagine an undergraduate chemistry student is at the gym and running on a treadmill. As they continue to maintain their speed, several physiological changes are occurring. For instance, you may observe an increase in heart rate, blood pressure, sweating, and breathing.

In order to exert their skeletal muscles, they need to continue inhaling oxygen gas to carry out cellular respiration, a biochemical process which produces energy in the form of ATP. However, as the rate of cellular respiration increases, cells continue to release more and more carbon dioxide into the bloodstream.

A schematic of cells releasing carbon dioxide into the capillaries.

This poses a problem. Carbon dioxide can react with water in the presence of an enzyme, known as carbonic anhydrase (CAH), to produce carbonic acid. Carbonic acid is an acidic species. Thus, we would expect the pH of the blood to decrease. However, excessive and continuous decreases in pH can lead to a condition known as acidosis. Acidosis can lead to fatigue, loss of appetite, nausea, and vomiting.

We do not see excessive acidosis in normal, healthy students. The pH is eventually restored to physiological pH and remains constant. So, how does this happen?

In order to answer this question, we need to examine what happens when carbon dioxide dissolves in the bloodstream.

A thorough inspection of the chemical equation reveals that carbonic acid (a weak acid) exists with its conjugate base. Thus, this system is a buffer system which is responsible for maintaining a constant pH in the bloodstream. In biochemistry, this is known as the bicarbonate buffer system (BBS).

Bicarbonate buffer system schematic which is one of many biological buffers
A schematic of the bicarbonate buffer system (BBS).

The Phosphate Buffer System

Let’s imagine our undergraduate chemistry student is done running the treadmill and decides to sit down. The student relaxes and the pH of the bloodstream begins to reach normal, homeostatic conditions. However, maintaining a constant pH is not only important for the bloodstream. It is also important for cells, the most basic unit of life.

However, cells do not rely on the bicarbonate buffer system (BBS) which is present in the blood. Rather, cells rely on a phosphate buffer system (PBS) as shown below.

Phosphate buffer system which is a common biological buffer
A schematic of the phosphate buffer system (PBS).

Biological Buffers Practice Problems

Problem 1

A researcher is conducting an experiment to determine the effects of prolonged exercise on the pH of blood in rodents. A control group is injected with a 5 μM sample of saline, while an experimental group is injected with a 5 μM sample of lactic acid to simulate prolonged exercise. The pH was monitored in the span of 1 h in 10.0 min increments. Predict whether the [H+] of the experimental group would be higher, lower, or equal to the control group.

Problem 2

A student is creating a biological buffer system and decides to use sulfuric acid. Explain why sulfuric acid would be a poor choice to mimic biological conditions.

Problem 3

Lysosomes are a class of organelles responsible for digesting food particles and recycling degraded mitochondria. However, mutations can occur which cause the lysosome to spill its contents into the cell. Explain how this would shift the phosphate buffer system (PBS).

Biological Buffers Problem Solutions

Problem 1

The experimental group would have a lower pH and thus, a higher [H+].

Problem 2

An acidic buffer system requires a weak acid (HA) and its conjugate base (A-). Considering sulfuric acid is a strong acid, it would be a poor choice to use.

Problem 3

It would shift the reaction to the reactants (left) as the system is becoming more acidic.

Further Reading – Biological Buffers

If you are interested on the topic, we recommend you to read this article!