Biochemical systems primarily generate energy through two key methods: oxidation reactions and cleavage reactions, also known as hydrolysis. In oxidation reactions, energy is produced in the form of electron carriers, specifically NADH and FADH2. For instance, during step 8 of the citric acid cycle, malate is converted into oxaloacetate. In this process, NAD+ gains electrons to become NADH, facilitated by the enzyme malate dehydrogenase. This reaction exemplifies how dehydrogenases are involved in oxidation processes.
Similarly, in step 6 of the citric acid cycle, succinate is transformed into fumarate. Here, FAD is reduced to FADH2 through another dehydrogenase reaction, which also involves the formation of a pi bond between the two carbon atoms, resulting in the conversion of succinate to fumarate.
The second method of energy production involves cleavage reactions, where high-energy bonds are hydrolyzed to release stored energy. A prime example is the hydrolysis of ATP. When ATP is cleaved in the presence of water, it releases an inorganic phosphate and energy, which can be utilized for various cellular processes. This reaction highlights the significance of breaking high-energy phosphate bonds in ATP to harness energy.
In summary, biochemical systems utilize oxidation reactions to produce electron carriers like NADH and FADH2, and cleavage reactions to release energy from high-energy bonds, particularly in ATP. Understanding these processes is crucial for comprehending how cells generate and utilize energy.