Journal of Energy Bioscience 2025, Vol.16, No.1, 21-30 http://bioscipublisher.com/index.php/jeb 23 2.3 Conformational changes in ATP hydrolysis and energy release When ATP is hydrolyzed, its terminal γ-phosphate group is cut off and becomes ADP (adenosine diphosphate) and an inorganic phosphate (Pi). This process releases a lot of energy, which cells can use to complete some tasks that require energy (Angeli et al., 2016; Hardie, 2018; Fontecilla-Camps, 2022). In some proteins, such as motor proteins or transport proteins, ATP binds to these proteins and hydrolyzes them, causing their structures to change, thereby driving the proteins to move or transport things outside the cell membrane (Glancy and Balaban, 2012; Fontecilla-Camps, 2022). When ADP and Pi leave the protein complex, the protein will undergo new structural changes so that it can return to its original state and prepare for the next round of work (Zhang et al., 2021; Fontecilla-Camps, 2022). 3 ATP Synthesis Mechanism 3.1 Glycolysis: ATP generation under anaerobic conditions Glycolysis is carried out in the cytoplasm of cells and is a very basic metabolic method. In the absence of oxygen, cells obtain energy through glycolysis. Simply put, it is to break down one molecule of glucose into two molecules of pyruvate and produce two molecules of ATP at the same time. Although the efficiency is not high, it is the main source of ATP when there is little oxygen or the cells grow very fast (Jourdain et al., 2021; White and Yang, 2022). The glycolysis process requires the participation of many enzymes, which is closely related to the energy status of the cell. Generally, we use the indicator [ATP]/[ADP][Pi] to judge the energy situation (Wilson and Matschinsky, 2022). When cells are in an oxygen-deficient environment, they can only rely on glycolysis to maintain energy, although each molecule of glucose only produces 2 ATP, which is much less than aerobic metabolism (Erecínska and Silver, 1989; Erecínska and Wilson, 2005). 3.2 Krebs cycle and oxidative phosphorylation in mitochondria When oxygen is sufficient, cells mainly rely on the Krebs cycle and oxidative phosphorylation in mitochondria to produce ATP. The Krebs cycle oxidizes acetyl-CoA produced by the decomposition of carbohydrates, fats and proteins to produce NADH and FADH2. These substances then enter the respiratory chain of the mitochondria and finally synthesize a large amount of ATP (Erecínska and Wilson, 2005; Vercellino and Sazanov, 2021). One molecule of glucose can produce approximately 36 ATP, while glycolysis only produces 2 (Erec í nska and Silver, 1989). The H+- ATP synthase in mitochondria plays a crucial role by utilizing the proton gradient on the membrane to synthesize ATP. The regulation of this process is complex, for example, the phosphorylation status of IF1 protein can affect the activity of H+- ATP synthase (Garcia Bermudez et al., 2015). Cells adjust the rate of ATP production according to their own needs (Erec í nska and Wilson, 2005). 3.3 Photosynthetic ATP synthesis in chloroplasts (plant cells) In plant cells, ATP can also be produced through photosynthesis. Photosynthesis converts light energy into chemical energy, producing ATP and NADPH at the same time. The "light reaction" of this process occurs on the thylakoid membrane, forming a proton gradient, which then drives the chloroplast ATP synthase to synthesize ATP. These ATP will be used in the "dark reaction" or Calvin cycle to fix carbon dioxide into organic matter such as sugars. Chloroplasts and mitochondria work together to maintain energy balance in cells. Mitochondria adjust metabolism according to the state of chloroplasts to help replenish ATP (Igamberdiev and Bykova, 2022). Intermediates such as malic acid and citric acid are transported back and forth between the two organelles, which can maintain the redox state of the cell and the reasonable distribution of energy, so that photosynthesis and respiration can proceed smoothly.
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