Enzymatic synthesis substrate transport

Thousands of distinct chemical reactions occur in a cell at any moment. A bacteria must simultaneously replicate its DNA, synthesize new enzymes, break down carbohydrates for energy, synthesize small components for protein and nucleic acid synthesis, and transport nutrients into and waste products out of the cell. Each of these processes is carried out by a series of enzymatic reactions called a pathway. The reactions of a pathway occur in succession, and the substrates for the pathways are often channeled through a specific set of enzymes without mixing. For example, in muscle cells, the glucose used to supply energy for contraction does not mix with the glucose used for transporting ions across the ceU membrane. 

Mitchell used chemiosmotic to describe enzymatic reactions that involve, simultaneously a chemical reaction and a transport process. The operational definition of coupling is shown in Figure 19-18. When isolated mitochondria are suspended in a buffer containing ADP, Pi, and an oxidizable substrate such as succinate, three easily measured processes occur (1) the substrate is oxidized (succinate yields fumarate), (2) 02 is consumed, and (3) ATP is synthesized. Oxygen consumption and ATP synthesis depend on the presence of an oxidizable substrate (succinate in this case) as well as ADP and Pi. 

There are some exciting prospects—as yet unexplored—for the constructive interplay between electrochemical processes and membrane transport/ catalytic processes. This may lead to novel routes of organic chemical synthesis or removal of toxic substances from process streams. Many important enzymatic reactions involve oxidative or reductive transformations of the substrate. These usually require the participation of a cofactor which serves as the vehicle for transfer of electrons between the enzyme-bound substrate molecule and the participating oxidant or reductant in solution [71, 72], For such electron transfer to take place, both substrate molecule and cofactor must be localized in close proximity at the active site of the... 

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