Metabolism of Other Hexoses

Group I ( Roll no. 1 – 50)

Presenters Kyaw San Lin & KK Thwe SunnKaung Kyaw Min & Kay Yu San

Slideshow preparation Kyaw Khan Zaw & Kyaw San Lin

CONTENTSIntroductionFructose metabolismGalactose metabolismMannose metabolismSummaryReferences

INTRODUCTION

Fate of dietary carbohydrates after digestion & absorption – intermediary metabolism

End products of carbohydrate digestion – monosaccharides: hexoses and pentoses

Principle hexoses – glucose, galactose & fructose

80 – 100% of the total amount absorbed from GI tract - glucose

Remaining 20% or less – mannose, galactose & fructose

After absorption, all enter the liver and converted mainly to glucose.

FRUCTOSE

SOURCES Disaccharide sucrose As free monosaccharide

METABOLISM

D-Fructose Fructo- ATP

kinase ↓Fructose-1-P

↓ ↓Glyceraldehyde DHAP

Aldolase B

The entry of fructose into the cells is not insulin dependent.

DISORDERS OF FRUCTOSE METABOLISM

EXCESSIVE FRUCTOSE CONSUMPTIONFructose ↑

Fructose 1-P ↑

Pi ↓ATP

↓

Gluconeogenesis ↓

Hypoglycemia

Protein synthesis ↓

Clotting factors & other

essential proteins ↓

AMP ↑

AMP degrad

ed

Hyperuricaemia

Gout

DHAP ↑

Glycerol 3-P ↑

entry into glycolysis ↑

Pyruvate ↑

Acetyl CoA ↑

Fatty acid ↑

Hypertriacyl-

glycerolaemia

Cholestrol ↑

Hypercholes-

trolemia

Atherogeni

c

ESSENTIAL FRUCTOSURIA

D-Fructose

Fructo- ATPkinase

Fructose-1-P

↓_↑

It is benign and asymptomatic.

HEREDITARY FRUCTOSE INTOLERANCE (FRUCTOSE POISONING)

Fructose-1-P

↓ ↓Aldolase B Glyceraldehyde DHAP

↑

o Autosomal recessive (1:20,000 births)o Symptoms similar to excessive fructose

consumption.o Sucrose & fructose must be removed from the

diet.

FORMATION OF SORBITOL

D-Glucose

NADPH+H+

NADP+

ALDOSEREDUCTASE

(not found in liver) D-

Sorbitol

SORBITOLDEHYDROGENASE

NAD+

NADH+H+

D-Fructose

FORMATION OF SORBITOL Increases in activity as the glucose

concentration rises In tissues that are not insulin-sensitive Fructose and sorbitol in

Lens → Cataract

Peripheral nerves → Neuropathy Renal glomeruli → Nephropathy

GALACTOSE

SOURCE lactose obtained from milk and its products

METABOLISM

in liverEnters glycolysis

in liver

LACTATING MOTHERS

In lactatingmammary gland

If Gal in diet is insufficient

DISORDER OF GALACTOSE METABOLISM

In lactatingmammary glandin liver

Enters glycolysis

If Gal in diet is insufficient

Galactosemiain liver

GALACTOSEMIA

Is a severe disease that is inhirited as an autosomal recessive trait ( 1 in 35,000 birth)

Physiologic consequences are similar to those found in hereditary fructose intolerance

A broader spectrum of tissues is affected.

Vomiting diarrhea occurs and enlarge liver with jaundice is common

GALACTOSEMIA

The accumulated galactose is shunted into side pathways such as that of galactitol production.

Accumulation of galactitol occurs in

lens of the eye → cataract

Liver → liver damage

Nerve → mental retardation

MANNOSE

SOURCES

Vegetables Hydrolysis of mannan gum

There is little mannose in dietary carbohydrates

METABOLISM

Mannose↓ Hexokinase

Mannose 6-P

Phosphomannoseisomerase↓

Fructose 6-P

SUMMARYGlucose

Glucose 6-P

Fructose 6-P

Fructose 1,6-bisphosphate

Dihydroxyacetonephosphate

Glyceraldehyde 3-PFructose

Fructose 1-P

Galactose

Galactose 1-P

Glucose 1-P

Mannose

Mannose 6-P

Glyceraldehyde

glycolysis

REFERENCES Department of Biochemistry: Biochemistry Handbook

Volume 3. University of Medicine Mandalay, 2012. Murray RK, Bender DA, et al: Harper’s Illustrated

Biochemistry, 28th ed. McGraw Hill, 2009. Harvey R, Ferrier D: Lippincott’s Illustrated Reviews:

Biochemistry, 5th ed. Lippincott Williams & Wilkins, 2011.

Bray GA, Nielsen SJ, Popkin BM: Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity. Am J Clin Nutr 2004;79:537–43.

Glyconutrition ForLife http://www.glyconutritionforlife.org/Science_of_Glyconutrients/Mannose.php accessed at 8 p.m, 23/7/2012.

Medical and healthcare design slides - Templates - Office.com http://office.microsoft.com/en-us/templates/CT010238352.aspx accessed at 8:27p.m.,13/7/2012

THANK YOU!