Cofactors are metal ions or organic compounds that associate with enzymes and are necessary for their function. Coenzymes are organic cofactors like coenzyme Q10 and NAD+, which help carry electrons or groups between reactions. A key coenzyme is ATP, which contains high-energy phosphate bonds and transfers energy and phosphates during phosphorylation reactions, coupling endergonic and exergonic processes to drive cellular metabolism.
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.
Table 5.1 Some Common Coenzymes
Table 5.1 Some Common Coenzymes
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).
Figure 5.20 ATP, an important energy currency in metabolism.
A ATP. Bonds between its phosphate groups hold a lot of energy.
Figure 5.20 ATP, an important energy currency in metabolism.
Figure 5 .21 How ATP and coenzymes couple endergonic reactions with exergonic reactions. Yellow arrows indicate energy flow. Compare F igures 5.8 and 5.20 C .