Biochemical Foundations of Human Life Processes - Volkov, N. I., & Nesen, E. N. 2000

Biochemical Foundations of Human Life Processes
Energy Metabolism in the Body
Mitochondria: The Powerhouses of the Cell

Cell/35.html">Mitochondria are the site of the final Stages of Nutrient oxidation and energy conversion into a form accessible for cellular use. They generate up to 90% of the ATP required for the body's vital activities. This specialized function of these cell Organelles is closely linked to their structural features. Mitochondria possess a smooth outer membrane and a folded inner membrane, as well as an internal core known as the matrix (Fig. 17).

The matrix contains Enzymes responsible for the Oxidation of Pyruvate and Fatty acids, alongside a high concentration of soluble enzymes of The Citric Acid Cycle. It also houses ADP, CoA, NAD, and all components required for mitochondrial Protein Synthesis.

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Fig. 17 Diagram of mitochondrial Structure, localization of The electron transport system (Respiratory Chain) and ATP formation, and the flows of key metabolites entering and produced within the mitochondrion

The outer membrane separates the interior of the mitochondrion from the Cell Cytoplasm. It contains various Proteins that form wide channels, allowing the easy passage of molecules with a Molecular Weight of up to 10,000 daltons. It also harbors enzymes that break down Lipids and facilitate their subsequent translocation into the mitochondrial matrix.

The inner mitochondrial membrane forms numerous folds projecting into the matrix, known as cristae. These cristae significantly increase the total surface area of the inner membrane. The structure of the cristae enables the orderly arrangement of numerous enzyme proteins along its surface. Embedded in the inner membrane are the primary enzyme complexes involved in electron transfer to oxygen (the respiratory chain) and the mediation of oxidative processes. On its matrix-facing surface are enzymes that synthesize ATP driven by the energy of oxidation (the ATP synthase complex). The inner membrane regulates The transport of metabolites into the matrix and the efflux of substances such as ATP, ADP, specific Amino Acids, fatty acids, Ca²⁺ ions, and others. This membrane is virtually impermeable even to many small molecules, as it maintains an electrochemical gradient of hydrogen protons (H⁺).

The narrow region between the outer and inner membranes constitutes the intermembrane space. It contains enzymes that catalyze the Transfer of phosphate from ATP to other NUCLEOTIDES and to free creatine molecules.

Mitochondria are mobile within The Cell and tend to localize to regions of high ATP utilization. In active Muscle tissue, they are positioned between myofibrils to supply the energy required for contraction. A single cell may contain up to 200 mitochondria, depending on the functional activity of the Organism. For instance, endurance aerobic training leads to a significant increase in the number of mitochondria in Skeletal Muscle.