 In this video I will discuss the importance of electrons in the transfer of energy in living systems to find oxidation, reduction, and cellular respiration. Many chemical reactions will involve the transfer of electrons from one atom to another. Oxidation is the loss of electrons in a chemical reaction, and reduction is the gain of electrons in a chemical reaction. Whenever there is oxidation, there will also be reduction, so a chemical reaction that involves the transfer of electrons is known as a reduction-oxidation reaction, or redox reaction. Let's look at the example of the catabolic pathway for the breakdown of glucose to produce carbon dioxide and water. This will also require the reagent oxygen, because oxygen will be the oxidizing agent that can accept electrons that are transferred from glucose as glucose gets oxidized. This catabolic pathway will release energy from the covalent bonds that are between the atoms in glucose. Some of that energy will be converted to heat, and some of that energy will be converted to the chemical potential energy of ATP molecules. Glucose is the reducing agent that gets oxidized as electrons are transferred from glucose to oxygen, and oxygen is the oxidizing agent that gets reduced as it accepts the electrons that came from glucose. Cellular respiration is a series of metabolic pathways that extracts the energy from the bonds in glucose molecules and converts it into a form that all living things can use, that is the chemical potential energy stored in the bonds of ATP molecules. Cellular respiration starts with the metabolic pathway known as glycolysis, which occurs in the cytoplasm. Glycolysis will convert one molecule of glucose that contains six carbon atoms into two molecules of pyruvate that each contain three carbon atoms. Pyruvate molecules will then enter into the mitochondria where the enzyme pyruvate dehydrogenase complex will catalyze the oxidation of pyruvate producing acetyl-coenzyme A and a carbon dioxide molecule. Acetyl-CoA will then enter into a metabolic pathway known as the Krebs cycle or the citric acid cycle. During the Krebs cycle, acetyl-CoA will be oxidized producing two molecules of carbon dioxide. Following the Krebs cycle, oxidative phosphorylation is a metabolic pathway that will accept high energy electrons coming from glycolysis, the pyruvate dehydrogenase complex, and the Krebs cycle. And as these high energy electrons move through oxidative phosphorylation, they're moving down what's known as the electron transport chain, a series of enzymes that carry out reduction oxidation reactions. In the end of oxidative phosphorylation, the energy that's been released from the oxidation of glucose is used to drive the endergonic chemical reaction of ATP synthesis. The high energy electrons will ultimately be transferred to oxygen in order to produce water, and so oxygen is the oxidizing agent for the overall process of glucose catabolism that will accept high energy electrons that ultimately come from the oxidation of glucose. Dehydrogenases and oxidases are the enzymes that catalyze reduction oxidation reactions. We can see an example here. The pyruvate dehydrogenase complex is a large enzyme that will catalyze the oxidation of pyruvate producing acetyl-CoA. As pyruvate is oxidized, an oxidizing agent known as NAD+, will be reduced to form NADH. Here we see the structure of NAD+, and NADH. NAD functions as an oxidizing agent to accept electrons as it is converted to NADH. Then NADH can function as a reducing agent that will be converted back to NAD+, as it delivers electrons to another oxidizing agent. NAD+, and NADH are an example of an electron carrier that will transfer high energy electrons from one metabolic pathway into another metabolic pathway. NADH will carry electrons into the electron transport chain within the mitochondria. The electron transport chain is a series of enzymes embedded in the inner mitochondrial membrane that will carry out reduction oxidation chemical reactions, starting with high energy electrons from NADH that will be passed down to reduce another oxidizing agent. Until eventually the oxidizing agent, Oxygen, will accept the high energy electrons that came from NADH in a reaction catalyzed by cytochrome C oxidase. Oxygen will be reduced to form water.