The sugar Fructose, found in high concentrations in fruits and food additives su

Question

The sugar Fructose, found in high concentrations in fruits and food additives such as high fructose corn syrup, is almost exclusively metabolized in the liver (with a small percentage metabolized in kidneys and intestine). The metabolism of this sugar in the liver involves the enzyme fructokinase, which converts it to fructose-1-phosphate. This product is then converted to glycogen, or more commonly converted to glyceraldehyde-3-P, which is then used in the synthesis of triglycerides, contributing to fat storage and obesity. Why is fructose not used in the liver, in glycolysis to generate ATP? Fructose is transported across membranes by GLUT5. What is GLUT5? Be specific!! How many carbons are in the product of fructolysis? What monomer of lipids has a similar structure? The enzyme Hexokinase is capable of phosphorylating both glucose and fructose. Let's say you genetically engineer human epithelial cells to express GLUT5. What would these guys then do with fructose they pick up? If you look at our evolution you'll see that we evolved to consume a diet fairly rich in glycogen and starch, and containing only small amounts of fruits with absolutely no high fructose corn syrup. Now we consume, on average, about 36 pounds of high fructose corn syrup a year. What did we get from our diet before? How as it used? How have things changed? What is happening now?

Explanation / Answer

1. Fructose enters the glycolyticpathway in the liver through the fructose 1-phosphate pathway. Thereafter cleavage of the fructose 1,6-bisphosphate into two three-carbon fragments which is then oxidized to pyruvate.

2. GLUT 5 is fructose transporter present on the small intestine, which allows for the transportation of fructose from the intestinal lumen into the enterocyte by facilitated diffusion due to fructose's high concentration in the intestinal lumen.

3. Fructose is converted to DHAP, glyceraldehyde and glyceraldehyde-3-Phosphate in the liver.

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