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Carbohydrates metabolism Glycolysis, cellular respiration and fermentation Living organisms transform biomolecules that are present in nutrients in order to produce energy and precursors for the synthesis of macromolecules. This transformation process is called metabolism. Metabolic pathways can be catabolic (they degrade molecules) and anabolic (they synthesize molecules). What is the metabolism? https://www.youtube.com/watch?v=ZkqEno1r2jk What is Aerobic Respiration? Photosynthesis Photosynthesis and cellular respiration https://www.youtube.com/watch?v=q-fKQuZ8dco Watch the video 1. What is mitochondrion? 2. Do you remember its function? Mitochondria Mitochondrion 1. Where does glycolysis take place? 2. What is glycolysis? 3. Could you describe the steps of glycolysis? Glycolysis Glycolysis Glycolysis is the catabolic pathway that leads to the breaking down of glucose (6 atoms of C) to pyruvate (3 atoms of C). Glycolysis Glycolysis: a closer look Glycolysis is divided into two phases: • preparatory phase – 2 ATP molecules are used to produce glyceraldehyde 3-phosphate; • pay-off phase – production of 4 ATP molecules and 2 pyruvate molecules. Glycolysis Glycolysis • Glucose (6C) • 2 ATP (as activation energy), 4 ADP, 2 NAD+ • Enzymes Requirements for Glycolysis • 2 of Pyruvate (ionized form of Pyruvic Acid) (3C) • 2 ADP, 4 ATP, 2 NADH The Products of Glycolysis Glycolysis: Nicotinamide Adenine Dinucleotide Plus, a redox coenzyme and energy carrier. Glycolysis Glycolysis Glucose is phosphorilated by ATP, then rearranged by an isomerase enzyme, then phosphorilated again by ATP. The fructose 1,6-bisphophate produced is then broken into two molecules of G3P, (glyceraldehyde 3-phosphate). energy investment phase Each G3P is oxidized by NAD+, so 2 NADH are produced. After, part of the energy of the intermediate organic molecules is captured inside 2 molecules of ATP (total: 4 ATP). In the end, two molecule of pyruvate are left. energy payoff phase To sum up… Puzzle Solution In aerobic conditions, pyruvate (3 C) is transferred inside the mitochondria, where the pyruvate dehydrogenase complex transforms it into acetylCoA. Pyruvate + NAD+ + CoA i Acetyl-CoA + CO2 + NADH + H+ From pyruvate to acetyl-CoA https://www.youtube.com/watch?v=q-fKQuZ8dco From pyruvate to acetyl-CoA Coenzyme A (CoA) Inside the mitochondrion (before the citric acid cycle can begin), pyruvate (3C) must be decarboxylated into acetate (2C), then oxidized and joined to a molecule of Coenzyme A, and so converted to acetyl CoA, which links the cycle to glycolysis. During the transformation process of pyruvate into acetyl CoA , a molecule of CO2 is released and a molecule of NADH is produced. From pyruvate to acetyl-CoA Acetyl CoA Acetyl-CoA enters the Krebs cycle (or citric acid cycle) where, in a series of steps, the molecule isoxidized to CO2 while at the same time reducing NAD to NADH. Krebs cycle https://www.youtube.com/watch?v=q-fKQuZ8dco The citric acid cycle, also called the Krebs cycle, oxidizes organic fuel derived from pyruvate, generating , for every turn: 1 ATP 3 NADH 1 FADH2 Krebs cycle FAD is the oxidized form of another redox coenzyme. FAD can accepts two electrons and two protons to become FADH2, the reduced form. FAD and FADH2 The citric acid cycle has eight steps, each catalyzed by a specific enzyme Krebs cycle • Acetyl CoA (2C) • 1 ADP • 3 NADP+ • 1 FAD into the Krebs cycle • 2 CO2 • 1 ATP • 3 NAD+ • 1 FADH2 Out of the Krebs cycle NADH and FADH2 transfer electrons to a system of proteins into the internal membranes of mitochondria. These proteins constitute the electron transport chain or respiratory chain. Electron transport chain https://www.youtube.com/watch?v=q-fKQuZ8dco Electron transport chain • The respiratory chain is a sequence of redox reactions, during which proteins in different complexes accept electrons and donate them immediately to the next complex. • Oxygen is the final electron acceptor. • The respiratory chain does not directly generate ATP, but energy in the form of proton motive force, which is necessary for oxidative phosphorylation Function of the electron transport chain Oxydation of NADH + H+ frees 2 electrons and 2 protons (H+). Electrons enter the transport chain, transferred from complex I to complex IV and to oxygen. With each redox reaction, new protons are generated, which are pumped across the mitochondrial membrane into the intermembrane space. The formation of a proton gradient High concentrations of H+ at one side of the membrane create an electrochemical gradient in which protons flow from the compartment at higher concentration to the compartment at lower concentration. The flux of protons pass through the F0 region of ATP synthase which activates the F1 subunit, where the synthesis of ATP takes place. Proton gradient and ATP synthase INTERMEMBRANE SPACE The proton concentration gradient and electric charge difference constitute a source of potential energy called the proton-motive force. Coupling of the protonmotive force and ATP synthesis is called chemiosmosis or chemiosmotic mechanism. Proton gradient and ATP synthase H+ Stator Rotor Internal rod Catalytic knob ADP + P i ATP MITOCHONDRIAL MATRIX The respiratory chain and ATP synthase produce ATP by a chemiosmotic mechanism Video Zanichelli su pc The respiratory chain and the oxidative phosphorilation Chemiosmosis Chemiosmosis Chemiosmosis Chemiosmosis Chemiosmosis Chemiosmosis Chemiosmosis https://www.youtube.com/watch?v=HZtXLhm7ISA Anaerobic conditions: fermentation • In the presence of O2, NADH and pyruvate are used to generate ATP in respiration. • In the absence of oxygen, carbohydrate metabolism does not follow the same pathway: pyruvate goes through alcoholic fermentation or lactic fermentation. • Fermentation turns NADH and pyruvate produced in the glycolysis phase into NAD+ and various small molecules depending on the type of fermentation. Anaerobic conditions: fermentation • it takes place in the muscle tissue and its product is lactic acid Lactic fermentation In lactic fermentation, pyruvate produced by glycolysis is reduced to lactic acid. The necessary electrons are provided by NADH + H+, generated during the pay-off phase. Glycolysis and Lactic acid fermentation • it takes place primarily in yeast and its product is ethyl alcohol. Alcoholic fermentation Pyruvate decarboxylase Alcohol dehydrogenase In some yeasts, alcoholic fermentation takes place: pyruvate goes through a decarboxylation and is converted to acetaldehyde, then reduced to ethanol thanks to NADH + H+. Glycolysis and Alcoholic fermentation Cellular respiration yields more energy than fermentation