Plant Physiology - Musiyenko, M. M. 2001

Chemical and molecular composition, structure, and functions of the plant cell
Mitochondria

Numerous Cell/35.html">Mitochondria are scattered throughout the Cell Cytoplasm, ranging in length from one to several micrometers and with a width of 0.5 µm (Fig. 14). Each mitochondrion is bounded by a double membrane, with the inner membrane forming numerous folds known as cristae. Most plant Cells contain hundreds or even thousands of mitochondria. Their number within a cell is determined by energy demands, as mitochondria act as The Cell's power plants.

Mitochondria serve as the sites of intracellular oxidation of respiratory substrates and contain the Enzymes of The Tricarboxylic Acid Cycle, the Electron Transport Chain, oxidative

phosphorylation, and other metabolic pathways.

The outer and inner membranes differ in both Chemical Composition and permeability. The outer membrane is characterized by a higher lipid content and a distinct enzymatic profile, and it is readily permeable to low-molecular-weight compounds, including respiratory substrates. Various organic molecules pass through this membrane and are subsequently oxidized to CO₂ and H₂O via a series of enzymatic reactions. During The oxidation of these molecules, the released energy is conserved in the phosphate bonds of ATP.

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Fig. 14. Schematic diagram of a mitochondrion:

1 — outer membrane, 2 — inner membrane, 3 — cristae, 4 — intermembrane space, 5 — matrix

Up to 10% of the COMPOSITION OF THE inner membrane, including the cristae, consists of electron transport chain components. Complex mushroom-shaped particles of the ATP synthase complex, which drive the synthesis of ATP from ADP and inorganic phosphate, are localized on the inner membrane.

The inner membrane acts as a barrier to many ions and possesses its own transmembrane transport systems for substance translocation.

The mitochondrial matrix contains calcium-containing granules, nucleoids, and Ribosomes. Calcium accumulation is coupled with Electron Transport and accompanied by the equivalent uptake of phosphate ions. By accumulating ions in the matrix, mitochondria participate in the overall process of cellular ion transport.

Like Plastids, mitochondria are semiautonomous Organelles, as they carry out Protein Synthesis independently of The Nucleus. The mitochondrial matrix houses its own protein-synthesizing machinery, comprising circular DNA, RNA molecules, and 70S ribosomes. The Mitochondrial Genome encodes up to 20 membrane and matrix Proteins. Approximately 95% of all mitochondrial proteins are synthesized by cytoplasmic ribosomes under nuclear control and post-translationally imported into the organelle.

Mitochondria are in constant motion, congregating in regions of high energy demand, occasionally fusing with one another, and dividing. The lifespan of a mitochondrion is several days. Mitochondria undergo their own morphogenesis. In meristematic cells, initial structures can be observed—rounded bodies up to 50 nm in diameter bounded by a double membrane. They gradually increase in size, and their inner membrane forms folds, or cristae. New mitochondria are formed through the division of pre-existing ones.

Detailed studies of mitochondrial Structure and genome suggest that they, much like METABOLISM/14.html">Chloroplasts, originated from Bacteria that established a symbiotic relationship within larger heterotrophic cells, the ancestors of eukaryotes.