Adp

creatine phosphate + H20 creatine

In the first reaction the energy is released directly. In the second, the energy is transferred to ADP and later released for muscular or other work. Creatine phosphate is sometimes called an active phosphate carrier. Similar substances are 1,3-diphosphoglyceric acid and phosphoenol-pyruvic acid.

Energy Stored in Active Acetate. The active acetate is the substance acetyl-CoA, which participates in intermediate metabolism. In terms of energy, formation of 1 mol of acetyl-CoA is equivalent to that of 1 mol of ATP.

Low-Energy Phosphate Compounds. Not all organic phosphates are of the high-energy type. Substances such as glucose-6-phosphate are phosphate compounds carrying a small amount of stored energy, such as 2-3 kcal/mol. If the above energy systems are summarized the oxidation or complete metabolism of glucose will yield the following:

Cellular Metabolism Processes

Within the cells, a series of complex biochemical processes is needed to degrade glucose (carbohydrate) to release the energy needed by the body. Three biological processes are involved: glycolysis, the citric acid cycle, and the respiratory chain. The glucose involved derives from food and internal production, which occurs mainly in the liver. In the cells of the liver, stored glycogen may be converted to glucose by the process of glycogenolysis; in the process of glu-coneogenesis, glucose is synthesized from noncarbohy-drate sources. However, as will be seen later, the muscles can also indirectly contribute the energy from cellular metabolism by participating in these processes. These processes are briefly defined in Table 4 and discussed in the following sections.

Glycolysis. The first step of carbohydrate metabolism is glycolysis, in which the six-carbon glucose is converted to a three-carbon substance (pyruvic or lactic acid), as indicated in Figure 5. Figure 6 illustrates the intermediate metabolic steps during the transformation of glucose to pyruvic acid. The interconversion between pyruvic and lactic acid occurs mainly in the muscle and will be discussed later. During the process of glycolysis, the conversion of 1

Food carbohydrate

Starch/ glycogen

Products Of digestion

.Dextrins, maltose

Dextrin maltose

Glucose

Maltose dextrin

Maltose

* Glucose

Lactose

Glucose, galactose

Sucrose

Glucose, fructose

Glucose, fructose

Glucose, fructose, galactose

Glucose, fructose, galactose

Glucose u*- Glucose Glucose Glucose Glucose (galactose) (fructose) (fructose, galactose)

Blood

Digestive system

Mouth

Stomach

Small intestine

Figure 3. Carbohydrate digestion.

Carbohydrate

Protein

Oxygen Vitamins Minerals Other factors

The Mediterranean Diet Meltdown

The Mediterranean Diet Meltdown

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