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The ruby-throated hummingbird has the fastest metabolic rate of any animal; the crocodile has among the slowest. At its peak, the metabolic rate of hummingbirds is actually the peak for diffusion-based cellular chemistry. Crocodiles are the opposite. When they submerge (for up to two hours!), everything slows down—blood flow, oxygen consumption, and the metabolic rates in individual cells, to levels that seem barely alive.
INTRODUCTION: Energy & Metabolism
Living things convert energy into organization. Using energy derived from food—or from a ray of sunshine—organisms “breathe life” into a handful of simple chemicals, turning them into a stunning variety of biological structures: from the familiar spiral of a strand of DNA to the twisted trunk of a thousand-year-old oak tree. How do organisms harness the energy they need to assemble and maintain such structures, and to power the processes that allow them to move and grow, develop and reproduce, and adapt and evolve? Utilizing energy and creating organization are the functions of metabolism, the elaborate web of chemical interactions that supports life itself. The reactions that make up metabolism produce energy-rich molecules and then break them down, extracting their energy to build something else. This cycle of energy storage and release allows living things to hold off the forces of decay, maintain their form over a lifetime, and pass their traits to future generations.
Understanding metabolism is essential for understanding life at all levels: in molecules, cells, organisms, and ecosystems. It may even hold the secret to why life exists. As microbiologist Franklin Harold writes in The Vital Force: A Study of Bioenergetics, “One cannot help but suspect that the great stream of energy that passes across the Earth plays a larger role in biology than our current philosophy knows: that perhaps the flood of power not only permitted life to evolve, but called it into being.
We will explore metabolism in cells and examine the chemical reactions that allow cells to capture energy and convert it to a form they can use to produce cell components. We examine how enzymes are organized to carry out the chemical business of the cell, and how metabolic activity is regulated. Disorders of metabolism are often associated with disease, and we look at how disruption of a single metabolic reaction can result in serious medical conditions. We conclude with a review of how researchers are applying their knowledge of metabolism to develop drugs and other products to preserve our health and our planet.
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