NADH and FADH2 are the reduced forms of NAD and FAD. The four stages of aerobic cellular respiration take place in the mitochondria and the cytoplasm of the cell. Cellular respiration that takes place in the presence of oxygen is called aerobic respiration and is the more efficient form of respiration. At the end of glycolysis, a six-carbon glucose molecule has been converted into two three-carbon molecules of pyruvate. Acetyl-CoA combines with oxaloacetate to form citric acid and start the Krebs cycle. At the end of the electron transport chain, the electrons combine with oxygen to form water. Respond to the following based on your reading.
Part 7, 1-4
Explain where each molecule of ATP produced during aerobic cellular respiration comes from. Include how NADH and FADH2 contribute to the production of ATP. Make sure to mention how many molecules of ATP are produced by the steps in aerobic cellular respiration. – see explanation
- NADH and FADH2 are the reduced forms of NAD and FAD. NADH and FADH2 are electron carriers that participate in cellular respiration. When NAD and and FAD gain electrons (i.e. become reduced), they also gain hydrogen atoms, switching to a different form, NADH and FADH2. Remember the mnemonic OILRIG (oxidation is lost, reduction is gain). The carriers are reduced because they have gained an electron.
- The four stages of aerobic cellular respiration take place in the mitochondria and the cytoplasm of the cell. The first stage of cellular respiration is called glycolysis. In glycolysis, glucose (a 6 carbon sugar) is broken down into 2 3 carbon sugars (pyruvate). This process occurs in the cytoplasm. In the mitochondria, pyruvate oxidation, the Krebs cycle and oxidative phosphorylation take place, completing the process.
- Cellular respiration that takes place in the presence of oxygen is called aerobic respiration and is the more efficient form of respiration. Aerobic respiration can occur only when oxygen is present. This is because oxygen is required as the final electron acceptor in the electron transport chain, where it is released as a water molecule as a by product. Aerobic respiration produces 36-28 ATP, whereas anaerobic respiration (no oxygen present) only produces 2 ATP.
- At the end of glycolysis, a six-carbon glucose molecule has been converted into two three-carbon molecules of pyruvate. As alluded to above, glycolysis involves the splitting of a glucose molecule to 2 molecules of pyruvate. Glycolysis can proceed with or without oxygen. It requires 2 ATP and generates 4 ATP, giving it a net gain of 2 ATP. There are over 10 enzymes involved in the process.
- Acetyl-CoA combines with oxaloacetate to form citric acid and start the Krebs cycle. Oxaloacetate is a 4 carbon molecule that begins the Krebs cycle. By combining with 2 carbon molecule of Acetyl CoA, it forms the 6 carbon molecule citrate. A series of 8 steps occur that produce NADH and FADH2, and release CO2 as a by-product.
- At the end of the electron transport chain, the electrons combine with oxygen to form water. As previously described, oxygen is the final electron acceptor that completes the electron transport chain. Oxygen is then reduced to water by electrons transported by FADH2 and NADH, completing the respiration process. In this way, oxygen is the terminal electron acceptor and produces a large amount of energy.
- Aerobic respiration begins with glycolysis. This is the process whereby 6C glucose is split into two 3C pyruvate molecules. This process requires 2 molecules of ATP, but releases 4 molecules of ATP, leading to a gain of 2 molecules of ATP. Glycolysis also produces 2 molecules of NADH (i.e. reduced NAD).
- Then, pyruvate oxidation takes place. During this process, the two 3 carbon pyruvate molecules are converted into two 2C acetyl- CoA molecules, releasing 2 molecules of CO2 in the process. This is sometimes called the transition reaction, and produces 2 molecules of NADH.
- Now, the Kreb’s cycle can begin. During the Kreb’s cycle, there are multiple intermediate products created through 8 biochemical steps. In the end, the Kreb’s cycle produces 2 molecules of ATP, 6 molecules of NADH, 2 molecules of FADH, and releases 4 molecules of CO2.
- The final step is oxidative phosphorylation (the electron transfer chain) which produces the most amount of energy. This stage is a series of reactions that moves electrons through a series of electron transporters (NADH and FADH), meaning hydrogen ions accumulate, and create a concentration gradient. This concentration gradient produces energy which is used to convert ADP to ATP, with oxygen as the final acceptor This process produces 34 molecules of ATP. Therefore, 38 molecules of ATP are produced in total by aerobic respiration, but 2 are required to start the process of glycolysis, giving a net gain of 36 molecules of ATP.