Figure 2.

Generation of reactive oxygen species (ROS) by the mitochondrial respiratory chain. Superoxide anions generated by the respiratory chain damage the respiratory chain itself and the mitochondrial DNA, which leads to changes in the respiratory chain that increase the production of the superoxide anion. Superoxide anions also damage the mitochondrial membranes, causing lipid peroxidation and leading to changes in membrane properties. Special superoxide dismutase (SOD) enzymes convert superoxide anions into hydrogen peroxide, which is then converted to water by peroxiredoxins (Prx) and glutathione peroxidase (GPx). Hydrogen peroxide plays a major redox-regulating (RR) role in this system. In mitochondria, it changes the activity of enzymes, in the cytosol, it affects the delivery of substrates into the mitochondria, whereas, in the nucleus, it alters the activity of transcription factors, causing the response kernel, which is reflected in increased protein expression of uncouplers (UCPs). UCPs are transported to the mitochondria, where they reduce the proton potential of the inner membrane, thereby reducing the production of the superoxide anion. Excessive production of hydrogen peroxide in the cytoplasm triggers autophagy processes, causes shortening of telomeres, potentially starts the process of apoptosis and causes increased expression of pro-inflammatory factors that can affect neighboring cells and the whole organism [27].