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INTRODUCTION Chapter 26 (pp. 1025-1033) Cellular Respiration and ATP Generation Mechanisms of ATP Generation • Phosphorylation is – bond attaching 3rd phosphate group contains stored energy • Mechanisms of phosphorylation – within animals • cellular respiration – in chlorophyll-containing plants or bacteria • photosynthesis • The food we eat is our only source of energy for performing biological work. • There are three major uses for the nutrients we ingest: – energy for active processes (ATP) – synthesized into structural or functional molecules (e.g., proteins, nucleic acids) – converted to fat or glycogen for later use as energy Fate of Glucose • All molecules have energy stored in the bonds between their atoms. • Glucose is the body’s preferred source of energy for synthesizing ATP. • The fate of absorbed glucose depends on the energy needs of body cells. • If the cells require immediate energy, glucose is oxidized by the cells to produce ATP. • Excess glucose can be stored as glycogen or fat. Overview of Cellular Respiration • In cytoplasm (1) • In mitochondria (2, 3 & 4) Cellular Respiration • glucose + O2 produces H2O + CO2 + energy • 4 steps are involved: (1) glycolysis (2) formation of acetyl CoA (transitional step to Krebs cycle) (3) Krebs cycle (= TCA or citric acid cycle) (4) electron transport chain Glycolysis • Glycolysis refers to the breakdown of the sixcarbon molecule, glucose, into two threecarbon molecules of pyruvic acid. – 10 step process occurring in cell cytosol – use two ATP molecules, but produce four, a net gain of two Glycolysis & Fate of Pyruvic Acid Aerobic Pathway – Pyruvic acid is converted to acetylCoA, which enters the Kreb’s Cycle Anaerobic Pathway (when O2 is scarce) – pyruvic acid is reduced to lactic acid – lactic acid rapidly diffuses out of cell to blood and to liver cells Formation of Acetyl Coenzyme A • Pyruvic acid enters the mitochondria • 3-carbon pyruvic acid converted to a 2-carbon acetyl group plus CO2 • Acetyl group is attached to Coenzyme A to form Acetyl coenzyme A, which enter Krebs cycle – coenzyme A is derived from pantothenic acid (vitamin B5) Krebs Cycle Krebs Cycle • The Krebs cycle is also called the citric acid cycle, or the tricarboxylic acid (TCA) cycle. It is a series of biochemical reactions that occur in the matrix of mitochondria Krebs Cycle • The large amount of chemical potential energy stored in intermediate substances derived from pyruvic acid is released step by step. • For every two molecules of acetyl CoA that enter the Krebs cycle, 6 NADH, 6 H+, 2 FADH2 and two molecules of ATP are produced. • The energy originally in glucose and then pyruvic acid is primarily in the reduced coenzymes NADH and FADH2. Electron Transport Chain • The electron transport chain involves a sequence of electron carrier molecules on the inner mitochondrial membrane. • As electrons are passed through the chain, there is a stepwise release of energy from the electrons for the generation of ATP. • In aerobic cellular respiration, the last electron receptor of the chain is molecular oxygen (O2). • The process involves a series of oxidationreduction reactions in which the energy in NADH and FADH2 is liberated and transferred to ATP. Summary of Aerobic Cellular Respiration • The complete oxidation of glucose can be represented as follows: C6H12O6 + 6O2 => 6CO2 + 6H2O + 36 or 38 ATP • During aerobic respiration, 36 or 38 ATPs can be generated from one molecule of glucose. – Two of those ATPs come from glycolysis. – Two come from the Krebs cycle. – The rest of the ATPs are generated in the electron transport chain. Electron Transport Chain • Pumping of hydrogen is linked to the movement of electrons along the electron transport chain • H+ ions are pumped from matrix into space between inner & outer membrane • As the high concentration of H+ rushes through the ATP synthase, ATP is generated