Cellular Respiration CellEnergetics 3 Overview of Respiration In the Krebs cycle, bonds in the carbon molecules are broken and the released energy is used to make electron carriers. In the electron transport chain, energy from electrons is used to power the proton pump. The proton pump supplies energy to synthesize ATP. Where glycolysis produced 2 ATPs from one glucose molecule, respiration produces about 36. Into the Mitochondria Before entering the mitochondria, pyruvate loses one carbon and is attached to a coenzyme, forming Acetyl CoenzymeA. AcetylCoA enters the mitochondria. The coenzyme breaks off, and the 2 carbon chain enters the Krebs cycle. The Krebs Cycle Also called the Citric Acid cycle. Discovered and described by Hans Krebs in Krebs was awarded a Nobel Prize in chemistry for his discovery. During the Krebs cycle, the carbon chains from glucose are broken down further. NADH, FADH, and a small amount of ATP are made. The Krebs Cycle The 2 carbon chain links with a 4-carbon molecule. As carbons are peeled off, NADH is reduced (gains electrons), and ATP is made with the released energy. Carbon is given off as carbon dioxide. The Krebs Cycle Here is a closer look at what happens during the cycle. The Electron Transport Chain Electrons from NADH move down the chain, releasing energy, which will be used to power ATP synthesis. 1. Electron donation from NADH, FADH 2. H+ ions pushed through the membrane 3. Oxygen picks up electrons and H+ ions, forming water. ATP synthesis Near the electron transport chain is a channel protein that also acts as an enzyme, often called the proton pump ATP Synthesis Electron carriers release electrons to the ETC. Energy from electrons is used to push H ions across the membrane, against a diffusion gradient. ATP Synthesis As H+ ions diffuse down their concentration gradient, the kinetic energy released powers the enzyme that carries out ATP synthesis. Other Energy Sources If you have enough ATP... ATP is unstable, and is not used for energy storage. If a cell has enough ATP at the moment, it will transform excess biomolecules into fatty acids so that they can be stored as fat for a later time. Monomers can transform to fat Simple sugars are broken apart in glycolysis. If the mitochondria does not need Acetyl CoA, the acetate is released and can be used to synthesize fatty acids to make fats for storage. Amino acids not needed for protein synthesis are stripped of their amine groups. The remaining carbon backbone can either be used to make Acetyl CoA, or can be used to synthesize fatty acids. Summary Pyruvate, from glycolysis, is transformed into a 2- carbon acetyl group and carried into the mitochondria. During the Krebs cycle, carbons are peeled off of the acetate, and the released energy is used to make the electron carriers NADH and FADH. NADH and FADH release electrons and H+ ions in the electron transport chain. Summary High-energy electrons travel down the electron transport chain, and the energy is used to push H+ ions across a membrane against a diffusion gradient. Kinetic energy released as the ions diffuse through a channel protein is used to power ATP synthesis. The result is about 36 ATP molecules from one molecule of glucose.