Energetics Outline

Energetics Outline - Chapter 25: Metabolism and Energetics...

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Chapter 25: Metabolism and Energetics An Overview of Metabolism, p. 916 Cells are chemical factories that break down organic molecules to obtain energy, which can then be used to generate ATP. Reactions within mitochondria provide most of the energy needed by a typical cell. To carry out these metabolic reactions, cells must have a reliable supply of oxygen and nutrients, including water, vitamins, mineral ions, and organic substrates (the reactants in enzymatic reactions). Oxygen is absorbed at the lungs; the other substances are obtained through absorption at the digestive tract. The cardiovascular system then carries these substances throughout the body. The term metabolism refers to all the chemical reactions that occur in an organism. Chemical reactions within cells, collectively known as cellular metabolism , provide the energy needed to maintain homeostasis and to perform essential functions. o Such functions include (1) metabolic turnover , the periodic breakdown and replacement of the organic components of a cell; (2) growth and cell division; and (3) special processes, such as secretion, contraction, and the propagation of action potentials. o All the cell’s organic building blocks collectively form a nutrient pool that the cell relies on to provide energy and to create new intracellular components. The breakdown of organic substrates is called catabolism . This process releases energy that can be used to synthesize ATP or other high-energy compounds. The ATP produced by mitochondria provides energy to support both anabolism —the synthesis of new organic molecules—and other cell functions. The most abundant storage form of carbohydrate is glycogen, a branched chain of glucose molecules; the most abundant storage lipids are triglycerides, consisting primarily of fatty acids. Proteins, the most abundant organic components in the body, perform a variety of vital functions for the cell, and when energy is available, cells synthesize additional proteins. The nutrient pool is the source of the substrates for both catabolism and anabolism. Carbohydrate Metabolism, p. 918 Most cells generate ATP and other high-energy compounds by breaking down carbohydrates— especially glucose. The complete reaction sequence can be summarized as follows: glucose oxygen carbon dioxide water The breakdown occurs in a series of small steps, several of which release sufficient energy to support the conversion of ADP to ATP. The complete catabolism of one molecule of glucose provides a typical body cell a net gain of 36 molecules of ATP. Although most ATP production occurs inside mitochondria, the first steps take place in the cytosol. The process of glycolysis breaks down glucose in the cytosol and generates smaller molecules that can be absorbed and utilized by mitochondria. o
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This note was uploaded on 12/29/2011 for the course BIOLOGY 24011 taught by Professor Pan during the Fall '11 term at HCCS.

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Energetics Outline - Chapter 25: Metabolism and Energetics...

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