Fatty acid storage form

Triglycerides, the storage form of fatty acids, are formed by attaching three fatty adds (as fetty acyl CoA) to glycerol. Triglyceride formation from fatty acids and glycerol 3-phosphate occurs primarily in liver and adipose tissue. 

Figure 29-3. Chemical structures of important vitamin A species and the provitamin A carotenoid i-carotene. All-fra/w-fi-carolene (T) is the most important provitamin A carotenoid, which can be converted to all-fraws-retinal and then all-tram-retinol (If), which by definition is vitamin A. All-tram-retinol can be esterified with long-chain fatty acids to form retinyl ester (III), the storage form of vitaminA in the body.The active form of vitamin A in vision is 11-cts-retinal (TV).The transcriptionally active forms of vitaminA are all-tram-retinoic acid (V) and 9-cts-retinoic acid (VI). 13-cA-Retinoic acid (VII) has poor transcriptional regulatory activity but is used clinically as isotretinoin to treat skin diseases.

Insulin resistance occurs when the normal response to a given amount of insulin is reduced. Resistance of liver to the effects of insulin results in inadequate suppression of hepatic glucose production insulin resistance of skeletal muscle reduces the amount of glucose taken out of the circulation into skeletal muscle for storage and insulin resistance of adipose tissue results in impaired suppression of lipolysis and increased levels of free fatty acids. Therefore, insulin resistance is associated with a cluster of metabolic abnormalities including elevated blood glucose levels, abnormal blood lipid profile (dyslipidemia), hypertension, and increased expression of inflammatory markers (inflammation). Insulin resistance and this cluster of metabolic abnormalities is strongly associated with obesity, predominantly abdominal (visceral) obesity, and physical inactivity and increased risk for type 2 diabetes, cardiovascular and renal disease, as well as some forms of cancer. In addition to obesity, other situations in which insulin resistance occurs includes... 

TRIACYLGLYCEROLS (TRIGLYCERIDES) ARE THE MAIN STORAGE FORMS OF FATTY ACIDS... 

Cholesterol, a polycyclic alcohol [Fig. 3(1)] is present in all animal tissues. It is a major constituent of cellular membranes, where it contributes to the fluidity of the membrane. The storage and transport forms of cholesterol are its esters with fatty acids. 

Fat is only an energy storage form (Fig. 17-4). Fat cannot be converted to carbohydrate equivalents. This is a very important point. Remember it The reason for this is a bit subtle. The carbon skeleton of fatty acids is metabolized to acetyl-CoA only. Glucose precursors such as oxaloacetate can be synthesized from acetyl-CoA by going around the TCA cycle. However, acetyl-CoA has 2 carbon atoms. Going around the TCA cycle burns off 2 carbon atoms (as C02). The net number of carbon atoms that ends up in oxaloacetate is then zero. No carbohydrate can be made from fat.5... 

In addition to fuel storage, fats and fatty acids are now known to have several key roles in the body, e.g. as messengers, precursors of molecular messengers, gene regulators, components of phospholipids (which form the major part of membranes) and possible modifiers of the immune response. 

Cholesterol is present in all animal tissues, and particularly in neural tissue. It is a major constituent of cellular membranes, in which it regulates fluidity (see p. 216). The storage and transport forms of cholesterol are its esters with fatty acids. In lipoproteins, cholesterol and its fatty acid esters are associated with other lipids (see p.278). Cholesterol is a constituent of the bile and is therefore found in many gallstones. Its biosynthesis, metabolism, and transport are discussed elsewhere (see pp. 172, 312). 

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