In cellular respiration, explain how electrons of glucose are involved in each process:
a) glycolysis
b) pyruvate
c) Krebs cycle
d) ETC
(leave blank for processes which don't apply)
a) In glycolysis, the electrons of glucose are not directly involved. Glycolysis is the first step of cellular respiration, which takes place in the cytoplasm of cells. It is an anaerobic process that involves the breakdown of glucose into two molecules of pyruvate. During glycolysis, glucose is converted into two molecules of glyceraldehyde-3-phosphate (G3P) through a series of enzymatic reactions. These reactions involve the transfer of high-energy phosphate groups from ATP to glucose, forming ATP and NADH in the process. However, no electrons are directly transferred in glycolysis.
b) In the conversion of pyruvate to acetyl-CoA, which occurs in the mitochondria, electrons play a small role. After pyruvate is transported into the mitochondria, it undergoes decarboxylation, which removes a carbon atom from pyruvate and releases CO2. This reaction generates high-energy electrons that are transferred to the molecule NAD+, resulting in the formation of NADH. However, it's important to note that the majority of the electrons from glucose are not released during this step but rather in the subsequent processes.
c) In the Krebs cycle, also known as the citric acid cycle or the tricarboxylic acid (TCA) cycle, the electrons from glucose are more actively involved. The Krebs cycle takes place in the mitochondria and involves a series of chemical reactions that further break down acetyl-CoA, derived from pyruvate, releasing CO2 as a byproduct. During this process, high-energy electrons are transferred to electron carriers such as NAD+ and FAD, resulting in the formation of NADH and FADH2. These electron carriers will then proceed to the next step, the electron transport chain (ETC).
d) In the electron transport chain (ETC), the final process of cellular respiration, the majority of the electrons from glucose are utilized. The ETC occurs in the inner mitochondrial membrane and involves a series of electron carrier molecules embedded in the membrane. As NADH and FADH2 from the previous steps donate their electrons to the ETC, the electrons are shuttled through a series of protein complexes. This electron transfer process generates energy and establishes a proton gradient across the membrane. Ultimately, the electrons combine with oxygen to form water. The energy produced from the flow of electrons is used to generate ATP through a process called oxidative phosphorylation.