Biochemical Reactions Require Energy

Many Biochemical Reactions Require Energy Biochemical Reactions Are Localized in the Cell Biochemical Reactions Are Organized into Pathways Biochemical Reactions Are Regulated Organisms Are Biochemically Dependent on One Another... 

Nicotinamide adenine dinucleotide (NAD) is the coenzyme form of the vitamin niacin. Most biochemical reactions require protein catalysts (enzymes). Some enzymes, lysozyme or trypsin, for example, catalyze reactions by themselves, but many require helper substances such as coenzymes, metal ions, and ribonucleic acid (RNA). Niacin is a component of two coenzymes NAD, and nicotinamide adenine dinucleotide phosphate (N/kDP). NAD (the oxidized form of the NAD coenzyme) is important in catabolism and in the production of metabolic energy. NADP (the oxidized form of NADP) is important in the biosynthesis of fats and sugars. 

In a very real sense, your body stores energy available from the metabolism of foods in the form of ATP. This molecule in turn supplies the energy required for all sorts of biochemical reactions taking place in the body. It does this by reverting to ADP, that is, by reversing reaction 17.6. The amount of ATP consumed is amazingly large a competitive sprinter may hydrolyze as much as 500 g (about 1 lb) of ATP per minute. 

Phosphate condensation reactions play an essential role in metabolism. Recall from Section 14.6 that the conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) requires an input of free energy ADP -I-H3 PO4 ATP +H2O AG° — +30.6kJ As also described in that section, ATP serves as a major biochemical energy source, releasing energy in the reverse, hydrolysis, reaction. The ease of interchanging O—H and O—P bonds probably accounts for the fact that nature chose a phosphate condensation/hydrolysis reaction for energy storage and transport. 

PN should provide a balanced nutritional intake, including macronutrients, micronutrients, and fluid. Macronutrients, including amino acids, dextrose, and intravenous lipid emulsions, are important sources of structural and energy-yielding substrates. A balanced PN formulation includes 10% to 20% of total daily calories from amino acids, 50% to 60% of total daily calories from dextrose, and 20% to 30% of total daily calories from intravenous lipid emulsion. Micronutrients, including electrolytes, vitamins, and trace elements, are required to support essential biochemical reactions. Parenteral... 

Many chemical reactions in seawater do not achieve equilibrium. The most notable are ones that involve marine organisms. Since organisms require energy, they cannot survive if their constituent biochemicals are at equilibrium. Equilibrium is also not likely to be achieved if some other process is adding or removing a chemical faster than equilibrium can be reattained. For example, calcium carbonate shells should spontaneously dissolve in deep ocean water, but some sink so fest that they can reach the sediments where they eventually become buried and, hence, preserved. In other words, the equilibrium approach is most applicable to reactions that attain equilibrium fester than any other competing processes acting on the chemical of interest. 

Biochemical reactions frequently require energy. The most common source of chemical energy used is adenosine triphosphate (ATP). The splitting of a phosphate from the ATP molecule can provide the energy needed to make an otherwise unfavorable reaction proceed in the desired direction. 

Reactions in living organisms are no different from reactions in laboratory flasks. Both follow the same laws, and both have the same kinds of energy requirements. For any biochemical reaction to occur spontaneously, AG must be negative. For example, oxidation of 1 mol of glucose, the principal source of energy for animals, has AG° = —2870 kj. 

Biochemistry is important in many fields of science in addition to medicine. For instance, biochemists investigate food by studying molecules such as vitamins, amino acids, fatty acids, various minerals, and water, all of which are dietary requirements for healthy nutrition. They also explain how these nutrients are absorbed by the body and what they do in the cells. For example, the question of how the body derives energy from dietary fats and oils involves a series of biochemical reactions explained by the biochemistry of the metabolic pathways. 

The ability to perform even the simplest of muscle movement requires complex coordination of the physical and chemical activities of the tissue. In recent years, nutritionists and exercise physiologists have described how the primary energy sources in food carbohydrates, fats, and proteins are transformed into the universal "currency" of biological energy, ATP. Oxidative metabolism processes the substrates through a cascade of enzymatic events to Insure maximal efficiency in energy conversion. At every level of this conversion, one or more metal ions serve as a cofactor to facilitate these biochemical reactions. The requirement of metals in the production of... 

In biological systems, the most frequent mechanism of oxidation is the removal of hydrogen, and conversely, the addition of hydrogen is the common method of reduction. Nicotinamide-adenine dinucleotide (NAD) and nicotinamide-adenine dinucleotide phosphate (NADP) are two coenzymes that assist in oxidation and reduction. These cofactors can shuttle between biochemical reactions so that one drives another, or their oxidation can be coupled to the formation of ATP. However, stepwise release or consumption of energy requires driving forces and losses at each step such that overall efficiency suffers. 

Many biochemical reactions that occur in cells require relatively high concentrations of potassium ion (K+). The concentration of K+ in muscle cells is about 0.15 M. The concentration of K+ in blood plasma is about 0.0050 M. The high internal concentration in cells is maintained by pumping K+ from the plasma. How much work must be done to transport 1.0 mol of K+ from the blood to the inside of a muscle cell at 37°C (normal body temperature) When 1.0 mol of K+ is transferred from blood to the cells, do any other ions have to be transported Why or why not Much of the ATP (see Exercise 68) formed from metabolic processes is used to provide energy for transport of cellular components. How much ATP must be hydrolyzed to provide the energy for the transport of... 

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