The temperature at which a biological experiment is conducted is a fundamental variable that determines the outcome and relevance of the results. In health-related and cell-based research, 37°C (98.6°F) is the standard incubation temperature. This setting is not arbitrary, but a deeply rooted standard driven by the necessity of recreating the conditions to which the biological samples are adapted.
The Physiological Standard
The selection of 37°C is directly tied to the core body temperature of humans and many other mammals. When scientists conduct studies using human cells, tissues, or pathogens that naturally infect humans, the goal is to simulate the environment within a living body, or in vivo, as closely as possible. Maintaining a constant 37°C allows for the most accurate observation of how these biological components function in their native setting.
This standard temperature ensures that any observed cellular processes, such as growth, metabolism, or response to a new drug, are relevant to human health. By mimicking the stable, internal conditions of the human body, researchers can generate data that is valid and translational for clinical applications. Without this physiological standard, the results of an experiment performed at room temperature, for instance, might not reflect what actually occurs inside a person.
The validity of the results is important, especially when investigating disease mechanisms or testing therapeutic agents. A cell’s behavior is highly dependent on its thermal environment, and small deviations can lead to significant changes in cellular function. Therefore, the 37°C benchmark acts as a control, allowing scientists to reliably compare findings across different laboratories and experiments worldwide.
Temperature’s Impact on Molecular Machinery
The physiological standard of 37°C is crucial because of its impact on proteins, particularly enzymes. Enzymes are biological catalysts that accelerate chemical reactions, and their efficiency is acutely sensitive to temperature changes. For human enzymes, 37°C represents the optimal temperature where they exhibit maximum activity.
As temperature increases, the kinetic energy of molecules also rises, leading to more frequent and energetic collisions between enzymes and their target molecules, known as substrates. This generally increases the reaction rate up to the optimal point. However, this delicate balance is easily disrupted by temperatures exceeding the physiological norm, which quickly leads to a loss of function.
Above 37°C, the increase in thermal energy can break the weak chemical bonds maintaining an enzyme’s three-dimensional structure, a process called denaturation. Once denatured, the enzyme’s specific shape, including the active site, is permanently altered. This loss of structure renders the enzyme unable to catalyze its reaction, causing a sharp decline in the overall biochemical process.
Conversely, at temperatures lower than 37°C, the molecules lack sufficient kinetic energy, and molecular collisions occur less often. This causes the enzyme activity to slow down, effectively putting the cellular processes into a state of dormancy. The optimal 37°C temperature is an evolutionary compromise, maximizing reaction speed without causing the breakdown of the cell’s protein machinery.
Contextualizing Temperature: Experiments That Deviate
While 37°C is the most common temperature in mammalian cell culture, it is not a universal biological requirement, and many experiments intentionally deviate from this standard. The required temperature for any experiment is determined by the natural habitat and biology of the organism being studied. For example, experiments involving common bacteria like Escherichia coli (E. coli) are often incubated at 37°C because many strains are adapted to the warm environment of the mammalian gut.
However, the yeast Saccharomyces cerevisiae, frequently used in genetics, is usually grown at a cooler 30°C. Similarly, organisms that thrive in cold environments, such as psychrophilic bacteria from polar regions, require low temperatures, sometimes close to 0°C. This is because their enzymes have evolved a different thermal optimum.
Thermophilic organisms, which are heat-loving microbes found in hot springs, present the opposite extreme, sometimes requiring temperatures above 80°C for growth. These exceptions underscore that the 37°C standard is specific to mesophilic organisms, particularly those involved in human biology. Varying the temperature in non-human experiments is necessary to accurately reflect the organism’s unique physiological conditions.