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Metabolic Pathways 1. Substrates are substances that enter reactions 2. Intermediates are the compounds formed between the start and the end of a pathway. 3. Enzymes are proteins that catalyze (speed up) reactions 4. Cofactors are small molecules and metal ions that help enzymes by carrying atoms or electrons. 5. Energy carriers are mainly ATP 6. End products are the substances present at the conclusion of a pathway. Introduction to Cellular Respiration • Cellular Respiration – Aerobic harvesting of energy from food molecules – Rearrangement of atoms during chemical reactions releases the potential energy – Generating ATP for cellular work ATP • Powers nearly all forms of cellular work • Adenosine Triphosphate – Adenine • Nitrogenous base – Ribose • Five carbon sugar – Tri-phosphate tail • Three phosphates (business end) • Potential energy stored in bonds – Triphosphate chain equivalent to a compressed spring – ATP ADP (releasing P releases energy) • Phosphorylation: – Transfer of a phosphate group (usually from an ATP molecule) to a molecule • ATP is a renewable source of energy Cellular Respiration • Chemical energy released from bonds of food molecules and stored in bonds of ATP • Produces 38 ATP molecules per Glucose molecule – 40% of energy in glucose – The rest released as heat Vocabulary • Redox Reaction: Movement of electrons from one molecule to another – Oxidation: Loss of electrons from one substance – Reduction: addition of electrons to a substance Cellular Respiration • Three Steps: – Glycolysis • Occurs in cytoplasm – Citric Acid Cycle (Krebs Cycle) • Takes place in the mitochondria **Minimal ATP made 1st two stages • They supply electrons to third stage – Electron Transport Chain • Inner membrane of the mitochondria • Energy from electrons used to generate ATP Key Players • ATP • NAD+ and FAD – Shuttle electrons in redox reactions • (dump trucks) • Key Reactions – Substrate-level phosphorylation • Phosphate transferred from substrate to ADP; forming ATP – Oxidative phosphorylation Substrate-Level Phosphorylation Glycolysis • Glucose split – two three carbon molecules – this requires 2 ATP molecules (investment) • Each three carbon molecule transfers electrons and H+ to carrier molecule – NAD+ NADH • Four ATP molecules made (payback) – Three carbon molecules converted to pyruvate Glycolysis Section 9-1 Glucose 1. Glucose enters the cell Go to Section: 2 Pyruvic acid To the electron transport chain Glycolysis Section 9-1 Glucose 2 Pyruvic acid 2. 2 ATP are used to split glucose apart to form two 3 carbon molecules call PEP Go to Section: Glycolysis Section 9-1 Glucose 2 Pyruvic acid 3. 4 ADP pick up energy to form 4 ATP 4. 2 NAD+ pick up electrons to form NADH To the electron transport chain 5. The ATP formed can now be used for normal cellular function 6. Pyruvate moves into the mitochondria and Krebs cycle Go to Section: Glycolysis Don’t get caught up in the details!! • The splitting of sugar • **What goes in: – Glucose – 2 ATP • **What comes out – 2 pyruvate molecules – 4 ATP (Net of 2) – 2 NADH (electron carrier) Krebs Cycle Pyruvate gets broke down to CO2, ATP, NADH, FADH2 Takes place in the mitochondria • Oxygen is required. • Pyruvic acid enters the mitochondria. carbon) (3 – 1 carbon kicks off to form carbon dioxide. – 2 remaining carbons form Acetyl-CoA join a 4 carbon molecule to form citric acid (6 carbons). – 1 carbon is kicked off to form carbon dioxide (5 carbon molecule) – 1 carbon is kicked off to form carbon dioxide (4 carbon molecule) • This 4 carbon molecule is then ready to accept another 2 carbon Acetyl-CoA group, which starts the cycle all over again. • 1(2) ATP molecule • 4 (8)NADH molecules • 1 (2)FADH molecule • 3 (6)Carbon dioxides Section 9-2 The Krebs Cycle Citric Acid Production Mitochondrion Go to Section: Section 9-2 The Krebs Cycle Citric Acid Production Mitochondrion Go to Section: The Citric Acid Cycle (Stage Two) • Per Glucose molecule: • What goes in: – 2 Pyruvate 2 Acetyl-CoA – 6 NAD+ * – 2 FAD • What comes out: – 8 NADH – 2 FADH2 – 2 ATP – 6 CO2 Electron Transport Chain • Oxidative Phosphorylation • Requires Oxygen. • The high energy electrons from NADH and FADH produced in the krebs cycle and glycolysis are passed to the electron transport chain. • 2 high energy electrons are transported down the chain from carrier to carrier through redox reactions • Energy from electrons actively transports H+ ions across inner membrane of the mitochondria • H+ ion gradient stores potential energy • H+ ions diffuse back across membrane due to concentration gradient • Membrane not permeable to H+ ions • They move across through a channel called ATP Synthase • As they move through, the channel uses energy from the flow of H+ to convert ADP to ATP • Each pair of high energy electrons that move down the electron transport chain provides enough energy to convert 3 ADP molecules into 3 ATP molecules. • At the end of the transport chain an enzyme combines electrons with hydrogen and oxygen to form water – Oxygen is the final electron acceptor Electron Transport Chain Section 9-2 Electron Transport Hydrogen Ion Movement Channel Mitochondrion Intermembrane Space ATP synthase Inner Membrane Matrix ATP Production Go to Section: Anaerobic Respiration