11.2 Impact of Temperature on Cell Function
Learning Objectives
- Explain how temperature influences enzyme activity and identify the consequences of temperature extremes on enzyme function.
- Describe how temperature affects the fluidity and function of phospholipid membranes, and explain how organisms adapt their membrane composition to different thermal environments.
Body temperature has a direct effect on cellular metabolism, influencing the structure and function of membranes, enzymes, and other proteins essential for life. Because most biochemical reactions are enzyme-catalyzed, even small changes in temperature can have wide-ranging effects on an animal’s physiology.
Temperature and Enzymatic Reactions
Enzymes are highly sensitive to temperature. Generally, as body temperature rises, enzyme activity rises as well. For every ten degree centigrade rise in temperature, enzyme activity doubles, up to an optimal point. Body proteins, including enzymes, begin to denature: their three-dimensional structure unravels, and they lose their function with high heat (around 50oC for mammals). Enzyme activity will decrease by half for every ten degree centigrade drop in temperature, to the point of freezing, with a few exceptions. Some cold-adapted species, such as Arctic fish, produce specialized proteins that allow enzymatic activity at subzero temperatures or can even survive freezing temporarily.
Figure 1.
Temperature and Phospholipid Membranes
The fluidity of cell membranes is also temperature-dependent. Membranes are composed mainly of phospholipids, which behave like a fluid mosaic. At high temperatures, membranes can become too fluid, compromising their integrity and making cells more permeable or even leaky. At low temperatures, membranes become more rigid, which can interfere with essential functions such as nutrient transport, signal reception, and enzyme binding.
Organisms adapt by adjusting the composition of their membranes. For example, cold-adapted animals may have more unsaturated fatty acids in their phospholipids, which remain fluid at lower temperatures.
Temperature and Proteins
Beyond enzymes, many structural and functional proteins are temperature-sensitive. High temperatures can lead to protein unfolding (denaturation), impairing muscle contraction, hormone function, and cellular repair processes. Low temperatures slow protein synthesis and folding, which can impact cell division and tissue maintenance.
Figure 2.
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