During the Krebs cycle, also known as the citric acid cycle or the tricarboxylic acid cycle, several reactions occur that involve the release and consumption of hydrogen atoms. Specifically, there are two reactions in the Krebs cycle where hydrogens are released.
1. Isocitrate dehydrogenase catalyzes the conversion of isocitrate to alpha-ketoglutarate. This reaction involves the removal of two hydrogen atoms from isocitrate, which are transferred to the coenzyme NAD+ (nicotinamide adenine dinucleotide), resulting in the formation of NADH and the release of two protons (H+).
2. Alpha-ketoglutarate dehydrogenase complex catalyzes the conversion of alpha-ketoglutarate to succinyl-CoA. Similar to the previous reaction, this step involves the removal of two hydrogen atoms from alpha-ketoglutarate, which are transferred to NAD+, forming NADH and releasing two protons (H+).
Overall, in the Krebs cycle, a total of four hydrogens (2 from isocitrate and 2 from alpha-ketoglutarate) are released as protons (H+), while four molecules of NADH are formed.
It is important to note that the Krebs cycle is a complex metabolic pathway, and this answer provides a simplified overview. There are additional reactions and steps in the cycle that involve the release and consumption of other molecules, such as water and carbon dioxide.