Triacylglycerols degradation

C. In prolonged fasting, triacylglycerol degradation in adipose tissue becomes maximal and sustained. 

In the absence of insulin and in response to glucagon stimulation, triacylglycerol degradation in adipose tissue runs unabated and the flood of fatty acids reaching the liver leads to ketone body synthesis and packaging of some triacylglycerols into VLDLs. 

Decreased triacylglycerol degradation Elevated insulin favors the dephosphorylated (inactive) state of hormone-sensitive lipase (see p. 187). Triacylglycerol degradation is thus inhibited in the well-fed state. 

Depending on an animal s current metabolic needs, fatty acids may be converted to triacylglycerols, degraded to generate energy, or used in membrane synthesis. Lor example, serum glucose levels are high immediately after a meal. The hor-... 

Dietary triacylglycerols are degraded to a small extent (via fatty acid release) by lipases in the low-pH environment of the stomach, but mostly pass untouched into the duodenum. Alkaline pancreatic juice secreted into the... 

The fatty acids released on triacylglycerol hydrolysis are transported to mitochondria and degraded to acetyl CoA, while the glycerol is carried to the liver for further metabolism. In the liver, glycerol is first phosphorylated by reaction with ATP. Oxidation by NAD+ then yields dihydroxyacetone phosphate (DHAP), which enters the carbohydrate metabolic pathway. We ll discuss this carbohydrate pathway in more detail in Section 29.5. 

S. N. Dudd, M. Regert and R. P. Evershed, Assessing microbial contributions to absorbed acyl lipids during laboratory degradations of fats and oils and pure triacylglycerols absorbed in ceramic potsherds. Organic Geochemistry, 29, 1345 1354 (1998). 

Waxes are biosynthesized by plants (e.g., leaf cuticular coatings) and insects (e.g., beeswax). Their chemical constituents vary with plant or animal type, but are mainly esters made from long-chain alcohols (C22-C34) and fatty acids with even carbon numbers dominant (Fig. 7.11). They may also contain alkanes, secondary alcohols, and ketones. The majority of wax components are fully saturated. The ester in waxes is more resistant to hydrolysis than the ester in triacylglycerols, which makes waxes less vulnerable to degradation, and therefore more likely to survive archaeologically. 

Figure 7.9 The degradation of triaq/lglycerol in adipose tissue to fatty acids and glycerol. The figure indicates the progressive release of fatly acids and the types of fatty acid that are usually present at each position and, therefore, released from each position as the triacylglycerol molecule. Sat. - Saturated. A lipase that is not regulated by hormones is also present is adipose tissue. It is continually active. Its role is described below.

One obvious symptom of a patient suffering from trauma is loss of body weight. This is due to increased mobilisation of both triacylglycerol in adipose tissue and degradation of protein in skeletal muscle. 

The decreased insulin/glucagon ratio activates degradation of glycogen, protein, and triacylglycerols. 

B. The triacylglycerols of chylomicrons are degraded to FFAs and glycerol in many tissues, but especially in skeletal muscle and adipose tissue. 

Certain classes of lipids are susceptible to degradation under specific conditions. For example, all ester-linked fatty acids in triacylglycerols, phospholipids, and sterol esters are released by mild acid or alkaline treatment, and somewhat harsher hydrolysis conditions release amide-bound fatty acids from sphingolipids. Enzymes that specifically hydrolyze certain lipids are also useful in the determination of lipid structure. Phospholipases A, C, and D (Fig. 10-15) each split particular bonds in phospholipids and yield products with characteristic solubilities and chromatographic behaviors. Phospholipase C, for example, releases a water-soluble phosphoryl alcohol (such as phosphocholine from phosphatidylcholine) and a chloroform-soluble diacylglycerol, each of which can be characterized separately to determine the structure of the intact phospholipid. The combination of specific hydrolysis with characterization of the products by thin-layer, gas-liquid, or high-performance liquid chromatography often allows determination of a lipid structure. 

T Biosynthesis and degradation of triacylglycerols are regulated such that the favored path depends on the metabolic resources and requirements of the moment. The rate of triacylglycerol biosynthesis is profoundly altered by the action of several hormones. Insulin, for example, promotes the conversion of carbohydrate to triacylglycerols (Fig. 21-19). People with severe diabetes mellitus, due to failure of insulin secretion or action, not only are unable to use glucose properly but also fail to synthesize fatty acids from... 

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