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• Cofactor: metal ion or organic compound that associates with an enzyme and is necessary for that enzyme’s function– Examples: vitamins, minerals, metal ions
• Coenzyme: an organic cofactor– Example: coenzyme Q10, NAD+
Figure 5.18 Example of a coenzyme. Coenzyme Q10 (above) is an essential part of the ATP-making machinery in your mitochondria. It carries electrons between enzymes of electron transfer chains during aerobic respiration. Your body makes it, but some foods—particularly red meats, soy oil, and peanuts—are rich dietary sources.
Figure 5.19 Heme. This organic molecule is part of the active site in many enzymes (such as catalase). In other contexts, it carries oxygen (e.g., in hemoglobin), or electrons (e.g., in molecules of electron transfer chains).
• ATP (adenosine triphosphate) functions as a cofactor in many reactions– Bonds between phosphate groups hold a lot of energy– When a phosphate group is transferred via the process of phosphorylation, energy is transferred along with it
Figure 5 .21 How ATP and coenzymes couple endergonic reactions with exergonic reactions. Yellow arrows indicate energy flow. Compare Figures 5.8 and 5.20 C .