Cellular RespirationHow cells release energy stored in veggies
Overview of Energy-Releasing PathwaysOrganisms stay alive by taking in energy. Photoautotrophs get energy from the sun and all other organisms, Heterotrophs get energy by eating plants and each other. The energy that drives this diversity of activity comes from the chemical bond energy of Adenosine Triphosphate ATP, the energy currency of the cell.
Pathways of Energy ReleaseAerobic Respiration-A pathway that produces 36 molecules of ATP is dependent on the presence of Oxygen Anaerobic Respiration-A pathway that produces 2 molecules of ATP operates in the absence of Oxygen is referred to as FermentationBoth pathways begin with the breakdown of Glucose (Glycolysis) produced during PhotosynthesisPhotosynthesis and Cellular Respiration are reactions that are dependent one on the other and are considered to be Coupled Reactions,
The First Stage GlycolysisThe site of the initial chemical reactions involved in the breakdown of 6 carbon Glucose is the cytoplasm of both prokaryotes and eukaryotesDuring glycolysis 2 molecules of ATP are used to produce 2, 3-carbon molecules called Pyruvate which can now enter the Mitochondria for the next step in the cellular respiration pathway.4 ATP are produce in this stage of glucose breakdown or catabolism, 2 will replace the ATPs invested to get the reaction started for a total net ATP production of 2 molecules.See Fig. 7.4
The Second Stage The Krebs CycleDuring the Krebs Cycle Acetyl-CoA bonds with the 2 Molecules of Pyruvate and transports them across the Mitochondrial membrane into the inner compartment region where the 2 Pyruvate molecules are transferred to oxaloacetate forming CitrateThe Pyruvates are stripped of their Carbon atoms which bond with O2 forming atmospheric Carbon Dioxide The other products of the Krebs Cycle are 8 NADH, 2,FADH2 and 2 ATP, which serve as electron and H+ carriers for the next step of the cellular respiration process (Fig. 7.7)
Third Stage of Aerobic RespirationThe Big Energy Payoff (Fig. 7.9)The 8 NADH and 2 FADH2 lose their electrons in an electron transfer chain reaction in the mitochondrial membrane releasing small bits of energy as the electrons pass through the molecules in the chain pumping H+ into the outer compartment of the mitochondrial membrane.As in photosynthesis equilibrium is reestablished by the movement of H+ into the inner compartment of the transport protein ATP synthase which drives the formation of ATP from ADP and unbound phosphateThe final step is the bonding of Oxygen to the last electron in the chain and H+ forming H2O-Water.
Fermentation Pathways-Anaerobic RespirationBacteria and protists that live in oxygen poor to oxygen absent environments, produce ATP by alternative pathwaysIn fermentation pathways, an organic substance that forms during the reaction is the final electron acceptor derived from glucose.Alcoholic fermentation (end product is ethyl alcohol) and lactate fermentation (conversion of pyruvate to lactate) both have a net energy yield of two ATP for each glucose molecule metabolized.