Chapter 8 BIOL1000 Dr. Mohamad H. Termos Cellular Respiration Chapter 8 BIOL1000 Dr. Mohamad H. Termos

Biology, 9th ed,Sylvia Mader Chapter 08 Cellular Respiration Breaks down nutrient molecules for the production of ATP Consumes oxygen and produces carbon dioxide (CO2) Aerobic - Usually involves the breakdown of glucose to CO2 and H2O Energy is extracted from the glucose molecule: Released step-wise Allows ATP to be produced efficiently Cellular Respiration

Glucose Catabolism Three major pathways of glucose catabolism Glycolysis Glucose (6 C)  two pyruvic acid molecules (3 C) Anaerobic fermentation Occurs in the absence of oxygen pyruvic acid  lactic acid Aerobic respiration Occurs in the presence of oxygen pyruvic acid  CO2 and H2O

Biology, 9th ed,Sylvia Mader Chapter 08 Cellular Respiration Cellular respiration includes four phases: Glycolysis Preparatory (prep) reaction Citric acid cycle Electron transport chain (ETC) Many steps in each phase NAD+ and FAD accept electrons to be transferred to other phases for more energy Cellular Respiration

Glucose Catabolism Two coenzymes of special importance to glucose catabolism NAD+ (nicotinamide adenine dinucleotide) Derived from niacin (B vitamin) NAD+ + 2 H  NADH + H+ FAD (flavin adenine dinucleotide) Derived from riboflavin FAD + 2 H  FADH2

Outside the Mitochondria: Glycolysis Biology, 9th ed,Sylvia Mader Chapter 08 Outside the Mitochondria: Glycolysis Glycolysis occurs outside mitochondria Two ATP are used Glucose  Pyruvate (3 carbon molecule) Gain two NADH Four ATP are produced; 2 are consumed Net gain of two ATP (4 ATP produced - 2 ATP consumed) Cellular Respiration

Outside the Mitochondria: Fermentation Biology, 9th ed,Sylvia Mader Chapter 08 Outside the Mitochondria: Fermentation Pyruvate is a “biological crossroads” If O2 is available to the cell, pyruvate enters the mitochondria for aerobic respiration. If O2 is not available to the cell, fermentation (anaerobic process) occurs in the cytoplasm. Cellular Respiration

Anaerobic Fermentation In an exercising muscle, demand for ATP may exceed the oxygen supply The only ATP cells can make under these circumstances are the 2 ATP produced by glycolysis Glycolysis cannot continue without supply of NAD+ NADH donates a pair of electrons to pyruvic acid reducing it to lactic acid Lactic acid leaves the cells Enter bloodstream and transported to the liver When oxygen becomes available the liver oxidizes it back to pyruvic acid Oxygen is created by exercising muscle

Anaerobic Fermentation Drawbacks of anaerobic fermentation Wasteful, because most of the energy of glucose is still in the lactic acid and has contributed no useful work Lactic acid is toxic and contributes to muscle fatigue Skeletal muscle is relatively tolerant of anaerobic fermentation, cardiac muscle less so The brain employs no anaerobic fermentation

Aerobic Respiration Most ATP generated in mitochondria, which requires oxygen. In the presence of oxygen, pyruvic acid enters the mitochondria

Inside the Mitochondria Biology, 9th ed,Sylvia Mader Chapter 08 Inside the Mitochondria The Preparatory (prep) Reaction: Connects glycolysis to the citric acid cycle. Pyruvate, enters the mitochondria. Pyruvate (3 carbons)  2-carbon group (Carbon dioxide released and electrons are picked up as hydrogen atom by NAD+ ) Citric Acid Cycle (Krebs cycle): Occurs in mitochondria. NADH and FADH2 capture energy rich electrons and ATP is formed. Produces: 4 CO2, 2 ATP, 6 NADH and 2 FADH2 per glucose molecule Cellular Respiration

Inside the Mitochondria Biology, 9th ed,Sylvia Mader Chapter 08 Inside the Mitochondria Electron Transport Chain (ETC): Takes place in the mitochondria. Receives electrons from NADH & FADH2 and produces ATP. Oxygen serves as the final electron acceptor and combines with hydrogen ions to form water. ATP moves out of mitochondria and is used for cellular work. It can be broken down to ADP and inorganic phosphate. These molecules are returned to the mitochondria for more ATP production Cellular Respiration

Inside the Mitochondria Biology, 9th ed,Sylvia Mader Chapter 08 Inside the Mitochondria Energy yield from glucose metabolism: Net yield per glucose: 1- From glycolysis – 2 ATP, 2-From citric acid cycle – 2 ATP, 3- From electron transport chain – 32 or 34 ATP Energy content: 1- Reactant (glucose) 686 kcal, 2- Energy yield (36 ATP) 263 kcal The rest of the energy from glucose is lost as heat Cellular Respiration

The Metabolic Pool Concept Biology, 9th ed,Sylvia Mader Chapter 08 The Metabolic Pool Concept Cellular Respiration