Chemistry:Q10 (temperature coefficient)

A plot illustrating the dependence on temperature of the rates of chemical reactions and various biological processes, for several different Q₁₀ temperature coefficients. The rate ratio at a temperature increase of 10 degrees (marked by points) is equal to the Q₁₀ coefficient.

The Q₁₀ temperature coefficient is a measure of temperature sensitivity based on the chemical reactions.

The Q₁₀ is calculated as:

[math]\displaystyle{ Q_{10}=\left( \frac{R_2}{R_1} \right )^{10 \,^\circ \mathrm{C}/(T_2-T_1) } }[/math]

where;

R is the rate

T is the temperature in Celsius degrees or kelvin.

Rewriting this equation, the assumption behind Q₁₀ is that the reaction rate R depends exponentially on temperature:

[math]\displaystyle{ R_2 = R_1 ~Q_{10}^{(T_2-T_1)/10 \,^{\circ} \mathrm{C}} }[/math]

Q₁₀ is a unitless quantity, as it is the factor by which a rate changes, and is a useful way to express the temperature dependence of a process.

For most biological systems, the Q₁₀ value is ~ 2 to 3.

In muscle performance

The effects of temperature on enzyme activity. Top - increasing temperature increases the rate of reaction (Q₁₀ coefficient). Middle - the fraction of folded and functional enzyme decreases above its denaturation temperature. Bottom - consequently, an enzyme's optimal rate of reaction is at an intermediate temperature.

The temperature of a muscle has a significant effect on the velocity and power of the muscle contraction, with performance generally declining with decreasing temperatures and increasing with rising temperatures. The Q₁₀ coefficient represents the degree of temperature dependence a muscle exhibits as measured by contraction rates. A Q₁₀ of 1.0 indicates thermal independence of a muscle whereas an increasing Q₁₀ value indicates increasing thermal dependence. Values less than 1.0 indicate a negative or inverse thermal dependence, i.e., a decrease in muscle performance as temperature increases.

Q₁₀ values for biological processes vary with temperature. Decreasing muscle temperature results in a substantial decline of muscle performance such that a 10 degree Celsius temperature decrease results in at least a 50% decline in muscle performance. Persons who have fallen into icy water may gradually lose the ability to swim or grasp safety lines due to this effect, although other effects such as atrial fibrillation are a more immediate cause of drowning deaths. At some minimum temperature biological systems do not function at all, but performance increases with rising temperature (Q₁₀ of 2-4) to a maximum performance level and thermal independence (Q₁₀ of 1.0-1.5). With continued increase in temperature, performance decreases rapidly (Q₁₀ of 0.2-0.8) up to a maximum temperature at which all biological function again ceases.

Within vertebrates, different skeletal muscle activity has correspondingly different thermal dependencies. The rate of muscle twitch contractions and relaxations are thermally dependent (Q₁₀ of 2.0-2.5), whereas maximum contraction, e.g., tetanic contraction, is thermally independent.

Muscles of some ectothermic species. e.g., sharks, show less thermal dependence at lower temperatures than endothermic species

See also

• Arrhenius equation
• Arrhenius plot
• Isotonic (exercise physiology)
• Isometric exercise
• Skeletal striated muscle
• Tetanic contraction