Cell Metabolism Overview

Cell metabolism is the set of life-sustaining chemical transformations within the cells of living organisms. The three main purposes of metabolism are the conversion of food/fuel to energy to run cellular processes, the conversion of food/fuel to building blocks for proteins, lipids, nucleic acids, and some carbohydrates, and the elimination of nitrogenous wastes. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments.

Cell metabolism is characterized by three fundamental energy demands: to sustain cell maintenance, to trigger aerobic fermentation, and to achieve maximum metabolic rate. The basal metabolic state of a cell is characterized by a maintenance energy demand, which is currently assumed to represent the energy cost incurred to maintain ions balance between the cell and its environment. This demand is often estimated from the extrapolation of the growth dependence of the energy demand to the basal state. However, it is not a constant independent of the cell growth rate.

Cells utilize glycolysis and oxidative phosphorylation to satisfy these energetic demands. Glycolysis has a low yield of 2 mol ATP/mol glucose but is characterized by a high horsepower (energy produced per volume of enzymes). Oxidative phosphorylation has a higher yield of 32 mol ATP/mol glucose but is characterized by a lower horsepower.

Enzymes are protein catalysts that speed up biochemical reactions by facilitating the molecular rearrangements that support cellular processes. They are flexible proteins that change shape when they bind with substrate molecules, which increases reaction rates. Many of the molecular transformations that occur within cells require multiple steps to accomplish, forming a coordinated series of chemical reactions known as metabolic pathways.

Cells must balance their catabolic and anabolic pathways to control their levels of critical metabolites and ensure that sufficient energy is available. For example, if supplies of glucose start to wane, cells will synthesize glucose from other materials or start sending fatty acids into the citric acid cycle to generate ATP. Conversely, in times of plenty, excess glucose is converted into storage forms, such as glycogen, starches, and fats.

Cell metabolism plays a crucial role in many research fields, including diabetes, obesity, pancreatic beta cell function, adipose tissue biology, lipid metabolism, cardiovascular biology, immunometabolism, bone homeostasis, aging and stress responses, sarcopenia, intermediary metabolism and cancer, neuronal control of metabolism and metabolic derangements causing neurodegeneration, circadian biology, stem cell energetics, exercise metabolism, the biology of mitochondria and other metabolic organelles, and peroxisomes and the ER.