H1-antihistamines work by binding to histamine H1 receptors in mast cells, smooth muscle, and endothelium in the body as well as in the tuberomammillary nucleus in the brain; H2-antihistamines bind to histamine H2 receptors in the upper gastrointestinal tract, primarily in the stomach.
3 NADH molecules and 1 FADH molecule is produced for every turn of the Krebs cycle. One molecule of glucose will result in two turns of the Krebs cycle because two pyruvate molecules are the result of one glucose molecule (pyruvate if fed into the Krebs cycle after it is converted into acetyl-CoA).
The Role of NADH and FADH2. Glucose catabolism ends during the Krebs cycle. This does not mean that all of the energy previously contained in glucose was used in the production of ATP. In fact, only one additional ATP molecule (per molecule of pyruvate) is produced by substrate-level phosphorylation in the Krebs cycle. The balance of extracted energy is tied up in NADH and FADH 2. In the next phase of cellular respiration, the high-energy electrons within NADH and FADH 2 will be passed to a set of membrane-bound enzymes in the mitochondrion, collectively referred to as the electron transport chain. These electrons will provide energy to do work.