Biochemistry

during dehydrogenation, and other substances containing unsaturated bonds that easily attach hydrogen and then transfer it to another acceptor. Non-heminic iron is involved in the transfer of electrons along the chain of cytochromes; it does not change the valency, but provides a “ tunnel ” effect that facilitates their migration. The transport of electrons and protons from oxidized substances to oxygen occurs through the respiratory chain. The process of transfer of hydrogen atoms through the entire complex enzymatic system of tissue respiration is associated with reversible transformations of enzymes from oxidized to reduced forms (Fig. 4.1). Thus, the first acceptor of electrons and protons taken from oxidized substances is NAD that is then reduced (NADH 2 ) and transfers hydrogen (electrons and protons) to the FAD. In this case, NADH 2 is oxidized and becomes capable of accepting a new pair of hydrogen ions, and FAD is reduced to FADH 2 . Then the electrons and protons pass from FADH 2 to coenzyme Q (ubiquinone). Further, the paths of electrons and protons diverge: electrons are transferred to oxygen through a system of cytochromes, and protons, bypassing a system of cytochromes, go directly to oxygen . This whole process takes place on the mitochondria, which are the "power stations" of energy production in cells. They have a special structure that differs from the structure of other organelles. Characteristic is the presence of many membranes forming partitions, internal protrusion. It is here that there are enzymes that sequentially catalyze all stages of oxidation of organic substances. 2H Substrate H J4 y NAD X yPADN^ у Oxidized I ! I Ubiquinone Substrate ^NADN j 4 PAD Reduced I — ” — I ATP NAD — * PAD L Substrate 2Fe 2+ 7Fe 3+ /2cyto-V 2cyto-Y (chrome Ы chrome cl < ^2Fe JtA «2Fe 2+A — ғ ----------- 1 ATP . 2Fe 2+ 2Fe H ' 2cyto- j 2cyto- Y chrome a 1 chrome а, ' *2Fe i+/ ^2Fe 2+A I __________________________ ,я O 2 ATP j L 2H O 2 =H 2 O Figure 4.1 - Diagram of the respiratory chain of cellular oxidation O 2 ' 110