The Nutritional State Regulates Lipogenesis

Excess carbohydrate is stored as fat in many animals in anticipation of periods of caloric deficiency such as starvation, hibernation, etc, and to provide energy for use between meals in animals, including humans, that take their food at spaced intervals. Lipogenesis converts surplus glucose and intermediates such as pyruvate, lactate, and acetyl-CoA to fat, assisting the anabolic phase of this feeding cycle. The nutritional state of the organism is the main factor regulating the rate of lipogenesis. Thus, the rate is high in the well-fed animal whose diet contains a high proportion of carbohydrate. It is depressed under conditions of restricted caloric intake, on

Acyl-CoA

COOH

Malonyl-CoA

3-KETOACYL-CoA SYNTHASE

R — CH2—°C - CH2 —C r\j S — CoA 3-Ketoacyl-CoA

3-KETOACYL-CoA REDUCTASE

NADP+

R —°CH2-CH - CH2—C r\j S - CoA 3-Hydroxyacyl-CoA

3-HYDROXYACYL-CoA DEHYDRASE

R —°CH2—0CH =*CH —*C r\j S — CoA 2-trans-Enoyl-CoA

2-trans-ENOYL-CoA REDUCTASE

NADP+

Figure 21-5. Microsomal elongase system for fatty acid chain elongation. NADH is also used by the reductases, but NADPH is preferred.

a fat diet, or when there is a deficiency of insulin, as in diabetes mellitus. These latter conditions are associated with increased concentrations of plasma free fatty acids, and an inverse relationship has been demonstrated between hepatic lipogenesis and the concentration of serum-free fatty acids. Lipogenesis is increased when su-

crose is fed instead of glucose because fructose bypasses the phosphofructokinase control point in glycolysis and floods the lipogenic pathway (Figure 20-5).

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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