Muscle energy storage

The ATP molecule is a universal energy carrier in the cell, and it is the principal one. It will sustain all reactions and processes requiring Gibbs energy active ion transport (ion pump operation), biosynthesis of proteins and other substances, muscle contraction, and so on. It is also employed for temporary energy storage in the cell. 

Fig. 21.2 Major effects of AMPK activation on numerous tissues. AMPK plays a key role in regulating whole body energy storage and expenditure. In hypothalamus, AMPK is involved in regulation of satiety and food intake. Activation of AMPK in the hypothalamus increases food intake, whereas inhibition decreases intake. In peripheral tissues such as skeletal muscle and liver, activation of AMPK increases energy expenditure by stimulating mitochondrial genesis and energy substrate utilization. AMPK also regulates lipolysis in adipose tissue and insulin secretion in pancreas.

External forces applied to tissues lead to stretching of collagen, elastic fibers, and smooth muscle in the associated ECMs as well as proteoglycan deformation and fluid flow from within the matrix. The application of these forces ultimately leads to matrix remodeling and energy storage. The question arises as to how external mechanical events trigger cellular synthesis. 

A final group of biologically important phosphate compounds is the phosphoramidates, which are characterized by the structure shown in Figure III-33. Phosphocreatine, an important energy storage compound in muscle, and phosphohistidine, an intermediate in several enzyme reactions, are two examples (Fig. III-34). 

Enzymes have been classified by an international Enzyme Commission (EC) and assigned EC numbers. Thus the enzyme creatine kinase (the muscle enzyme that catalyses the energy storage reaction ATP + creatine —> ADP + phosphocreatine) has the EC number 2.7.3.2, these numbers successively referring to a transferase function (2), a phosphotransferase function (7), phosphotransfer with a nitrogen (N) acceptor (3) and creatine kinase per se (2). 

The triglycerides of foods are located mainly in the energy storage sites of the animal or plant specialized cells called adipocytes in meat (muscle), microscopic particles called lipoproteins in milk, and seeds in plants. 

Starch is the polysaccharide that plants use for storing energy. Many animals make use of a similar energy-storage carbohydrate called glycogen. It is often stored in muscle tissue as an energy source. 

Supplementation with creatine has not been found to enhance aerobic work performance despite measurable increases in muscle creatine and phosphocreatine, suggesting that energy transfer in muscle cells is not normally limited by the total creatine concentration. However, ability to perform intermittent high-intensity work is enhanced, indicating that the energy storage function of PC is increased by creatine supplementation. 

Muscle converts chemical free energy from ATP hydrolysis into mechanical work with an efficiency approaching 80% under optimal circumstances. ATP is only an intermediary in energy storage in red muscles. Its concentration remains relatively constant during long exercise, as shown in the NMR studies of Figure 12,14. 

Creatine Arginine, glycine, and S-adenosyl methionine (SAM) Liver Forms creatine phosphate in muscle for energy storage. Excreted as creatinine. 

Reflect and Apply (a) The major energy storage compound of animals is fats (except in muscles). Why would this he advantageous (h) Why don t plants use fats/oils as their major energy storage compound ... 

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