CHAPTER OUTLINE
7.1 Overview of Cellular Respiration
Cellular respiration is the release of energy from molecules such as glucose accompanied by the use of this energy to synthesize ATP molecules.
NAD+ and FAD
Cellular respiration involves many individual reactions catalyzed by the coenzymes Nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD), which are used as electron carriers.
Phases of Cellular Respiration
The metabolic pathways of cellular respiration couple the release of energy within a glucose molecule to the production of ATP.The phases of cellular respiration include glycolysis, the preparatory reaction, the citric acid cycle, and the electron transport chain.
7.2 Outside the Mitochondria: Glycolysis
Glycolysis, which takes place within the cytoplasm, is the breakdown of glucose to two pyruvate molecules.
Energy-Investment Steps
As glycolysis begins, two ATP are used to activate glucose and the resulting molecule splits into two C3 molecules (G3P, glyceraldehydes 3-phosphate).
Energy-Harvesting Steps
Oxidation of G3P and subsequent substrates results in four high-energy phosphate groups used to synthesize four ATP, so there is a net gain of 2 ATP.
Input and Outputs of Glycolysis
Inputs = 6C glucose, 2 NAD+, 2 ATP, 4 ADP +4P
Outputs = 2 (3C) pyruvate, 2 NADH, 2 ADP, 4 ATP total
Two ATP net gain.
7.3 Outside the Mitochondria: Fermentation
Fermentation is an anaerobic pathway a cell may utilize if oxygen is limited when breaking down glucose.
Advantages and Disadvantages of Fermentation
Fermentation is essential to humans despite its low yield of only two ATP. However, lactate is toxic to cells.
Energy Yield of Fermentation
Fermentation produces only two ATP by substrate-level ATP synthesis.
7.4 Inside the Mitochondria
Preparatory Reaction
The preparatory reaction occurs inside the mitochondria. It produces the molecule that can enter the citric acid from pyruvate.
Citric Acid Cycle
The citric acid cycle is a cyclical metabolic pathway located in the matrix of mitochondria. It oxidizes acetyl groups to carbon dioxide, making ATP by substrate- level ATP synthesis, and producing NADH + H+ and FADH2.
Electron Transport Chain
The electron transport chain is located in the cristae of the mitochondria and is a series of carriers that pass electrons from one to the other, resulting in energy that is stored as a hydrogen ion gradient.
Organization of Cristae
The electron transport chain is located within the cristae of the mitochondria, which increases the internal surface area of a mitochondrion. The complexes in the chain establish a hydrogen ion gradient between the matrix and the intermembrane space. This gradient is used to synthesize ATP by chemiosmosis.
Energy Yield from Cellular Respiration
The complete breakdown of glucose results in 36 or 38 total ATP.
Efficiency of Cellular Respiration
Approximately 39% of the available energy in a glucose molecule is usually transferred to ATP.
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