Metabolism of Fructose and Galactose Flashcards Preview

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Flashcards in Metabolism of Fructose and Galactose Deck (13)
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1

name the GLUT transporter of fructose and the dietary sources of fructose

dietary fructose absorbed by GLUT-5

  • sucrose (digested by intestinal sucrase)
  • fruits and honey
  • HFCS (55% fructose/45% glucose)
  • sorbitol; can form fructose by sorbitol dehydrogenase

2

describe benign fructosuria (essential fructosuria)

  • deficiency of fructokinase in liver
  • on ingesting surcorse, fructose is not metaboilzed and is excreted in urine in these children
    • Clinitest with urine reveal the presence of a reducing sugar
    • no toxic metabolites of fructose accumulate in liver; asymptomatic

3

describe hereditary fructose intolerance

  • deficiency of aldolase B in the liver
  • ingestion of sucrose or fructose results in trapping of fructose 1-phosphate in hepatocytes
    • trapping of Pi results in ATP deficiency -> inhibits gluconeogenesis -> hypoglycemia
    • trapping of Pi also inhibits glycogenolysis -> hypoglycemia
  • inhibition of gluconeogenesis + glycogenolysis = hypoglycemia (drowsy, apathetic)
    • hypoglycemia occurs following consumption of sucrose/fructose, NOT in fasting state

4

patients with hereditary fructose intolerance who continue to ingest fructose/sucrose/sorbitol in their diet can manifest with features of ______ and manifest with _____

patients with hereditary fructose intolerance who continue to ingest fructose/sucrose/sorbitol in their diet can manifest with features of hepatocellular failure and manifest with jaundice 

5

describe the location of fructose in patients with hereditary fructose intolerance

  • urine analysis detects the presence of a reducing sugar (fructose)
  • children with fructose intolerance DO NOT have cataracts

6

describe the synthesis of fructose from glucose (polyol pathway)

7

contrast age of diagnosis of fructose intolerance with galactose intolerance

  • fructose intolerance usually around 6-8 months since there is no fructose in breast milk; usually seen when fruits are introduced into diet
  • galactose intolerance is seen immediately since galactose is found in breast milk

8

dietary galactose is absorbed into the intestinal mucosal cell by _____

dietary galactose is absorbed into the intestinal mucosal cell by SGLT-1

9

describe galactose metabolism

10

what enzyme is deficient in classical galactosemia and how does it affect organs

  • galactose 1-phosphate uridyl transferase (GALT) which is autosomal recessive 
  • accumulation of galactose 1-phosphate in the liver traps phosphate and inhibits gluconeogenesis + glycogenolysis
    • jaundice and hepatomegaly
  • galactose in the lens results in formation of galactitol (by actvity of aldose reductase); osmotically active and increases water content of the lens
  • galactose 1-P accumulates in the brain resulting in neurological damage 

11

describe non-classical galactosemia

  • deficiency of galactokinase
  • accumulation of galactitol results in early cataract formation
  • urine is positive for reducing sugar

12

describe lactose synthesis

  • lactose synthesis takes place in the mammary gland during lactation
  • alpha-lactalbumin (protein B) synthesis is stimulated by prolactin (secreted during lactation)
    • alpha-lactalbumin (protein B) is found only in lactating mammary gland

13

summarize the enzyme deficiencies in the fructose/galactose metabolism disorders