SEQ’S :

st 1 priority

 How does high fructose diet lead to flooding of cells with cholesterol and triacylglycerol? Give the mechanism. What are the enzyme deficiencies in essential fructosuria and  hereditary fructose intolerance? Write down reactions catalyses by these enzymes  What is the cause of hyperuricema, hypoglycemia, vomiting and muscle weakness fructose intolerance?  Which defect cause galactosemia? Write reaction catalyzed by deficient enzyme How lactose is synthesized in mammary glands?

nd 2 priority www.themedicalglobe.com / www.mgElearning.net Page 1 of 5   Give hepatic metabolism of fructose  What are the biochemical events involved in causation of cataracts in uncontrolled diabetes mellitus? How galactose component of lactose is converted to glycogen in the liver?

MCQ’S : Do not skip any 

 The major source of fructose is the disaccharide sucrose and is present as monosachhride is fruits and honey  Fructokinase provides the primary mechanism For fructose phosphorylation into fructose 1-P Fructose 1-phosphate is cleaved by aldolase B (also called  fructose 1-phosphate aldolase) to dihydroxy acetone  phosphate (DHAP) and glyceraldehyde  Aldolase A is found in most tissues  aldolase B is found in liver Aldolase C is found in brain  The first symptoms of HFI appear when a baby is weaned from milk and begins to be fed food containing sucrose  Hexokinase phosphorylates mannose, producing mannose 6- phosphate  Mannose 6-P is isomerized to fructose 6-phosphate by  phosphomannose isomerase. Most intracellular mannose is synthesized from fructose ESSENTIAL FRUCTOSURIA ; Lack of fructokinase www.themedicalglobe.com / www.mgElearning.net Page 2 of 5 

HEREDITARY FRUCTOSE INTOLERANCE ("FRUCTOSE  POISONING"); Absence of aldolase B leads to intracellular  trapping of fructose 1-P. Aldose reductase reduces glucose, producing sorbitol (glucitol)  sorbitol dehydrogenase oxidize the sorbitol to produce fructose  The major dietary source of galactose is lactose (galactosyl β- 1,4-glucose) obtained from milk and milk products.  Galactokinase phosphorylates Galactose producing galactose 1- phosphate galactose 1-phosphate uridyltransferase (GALT) forms UDP-  Galactose from Galactose, in exchange reaction with UDP- glucose  galactose 1-phosphate uridyltransferase (GALT); galatokinase deficiency If galactose is not provided by the diet (for example in lactose-  intolerant), all tissue requirements for UDP-galactose can be met by the action of UDP-hexose 4-epimerase on UDP-glucose  Lactose is a disaccharide that consists of a molecule of β- galactose attached by a β(1→4) linkage to glucose.  Lactose is synthesized in the Golgi by lactose synthase (UDP- galactose:glucose galactosyltransferase),  Lactose synthase transfers galactose from UDP-galactose to  glucose, releasing UDP Protein A of Lactose synthase is a β-D-galactosyltransferase In tissues other than the lactating mammary gland, Protein A transfers galactose from UDP-galactose to N-acetyl-D-

www.themedicalglobe.com / www.mgElearning.net Page 3 of 5  glucosamine, forming the same β(1→4) linkage and producing N-acetyllactosamine  Protein B part of lactose synthase is found only in lactating  mammary glands. Part B is α-lactalbumin Part B synthesis is stimulated by the peptide hormone, prolactin. Figure:    12.3  12.4 12.5 12.7

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