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1. GOVERNMENT OF SIERRA LEONE MINISTRY OF HEALTH AND
SANITATION SCHOOL OF CLINICAL SCIENCE MAKAMBO MAKENI
MODULE –MEDICAL BIOCHEMISTRY
TOPIC –GALATOSE FRUCTOSE METABOLISM
LECTURER –DR MASERAY C KAMARA
GROUP – NINE 9

2.  1-ANSUMANA K KAMARA
 2-RAMATU SALL
 3-JAMES DUMBUYA
 4-FORAY KONDEH
 5-EDMOND B KAMARA
 6-MABINTY KANU
 7-SALIFU L SAMURA
GROUP MEMBERS

3.  We need to remember that galactose is a metabolite
of lactose
 Lactose is broken down to one molecule of glucose
and galactose
GALACTOSE METABOLISM

4.  There are no catabolic pathways to metabolize galactose, so
the strategy is to convert galactose into a metabolite of
glucose
 The first reaction in the galactose–glucose interconversion
pathway is the phosphorylation of galactose to galactose 1-
phosphate by galactokinase in the liver

5.  Galactose 1-phosphate then acquires a uridyl group from
uridine diphosphate glucose (UDP-glucose)

6.  The products of this reaction, which is catalyzed by
galactose 1-phosphate uridyl transferase, are UDP-galactose
and glucose 1-phosphate
 The galactose moiety of UDP-galactose is then epimerized
to glucose.
 The configuration of the hydroxyl group at carbon 4 is
inverted by UDP-galactose 4-epimerase
 Note that UDP-glucose is not consumed in the conversion of
galactose into glucose, because it is regenerated from UDP-
galactose by the epimerase
 Finally, glucose 1-phosphate, formed from galactose, is
isomerized to glucose 6-phosphate by phosphoglucomutase

7.  Causes a condition known as Lactose intolerance, or hypolactasia
 Lactose is fermented in the colon to lactic acid, methane and
hydrogen gas
 The gas produced creates the uncomfortable feeling of gut
distention and the annoying problem of flatulence(bloating)
 Lactic acid and lactose are osmotically active, they draw water
into the intestines which leads to diarrhea, dehydration
 Diagnosis is based on a positive hydrogen breath test after an oral
lactose load.
 Best treatment is to avoid foods containing lactose, milk and milk
products (except unpasteurized yogurt, which contains active
Lactobacillus) or by lactase pills.
Lactase deficiency

8.  important enzymes in galactose metabolism are:
 Galactokinase
 Galactose 1-phosphate uridyltransferase
 The disruption of galactose metabolism is referred to
as galactosemia
 The most common form is called clasic galactosemia
which is an inherited deficiency of Galactose 1-
phosphate uridyltransferase
Galactosemia

9.  symptoms manifest on day three of life and affected
infants fail to thrive
 Vomiting and diarrhea occur after milk ingestion, liver
cirrhosis, jaundice which does not resolve on
phototherapy, severe bacterial infections, Failure to
thrive, lethargy, hypotonia, and mental retardation
are other common and apparent features
 Babies will also develop cataracts
Cont….

10.  mandatory screening of newborns for galactosemia is
recommended through a newborn heel prick test in
the early weeks of life
 formulas containing galactose-free carbohydrates are
given
 The life expectancy will then be normal with an
appropriate diet.
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11.  A cataract is the clouding of the normally clear lens of the
eye
 The eye lens has high concentrations of aldose reductase
enzyme.
 In absence of galactose metabolizing enzymes, aldose
reductase reduces galactose to galactitol
cataracts

12.  Galactitol is osmotically active leading to osmotic
damage of the lens
Cont......

13. FRUCTOSE METABOLISM

14. FRUCTOSE METABOLISM

15.  Fructose is found in honey and fruit and as part of the
disaccharide sucrose (common table sugar)
 Sucrose is hydrolyzed by intestinal brush border sucrase,
and the resulting monosaccharides, glucose and fructose,
are absorbed into the portal blood
 The liver phosphorylates fructose and cleaves it into
glyceraldehyde and DHAP
 The important enzymes are,
 Fructokinase
 Fructose 1-P aldolase (aldolase B)

16.  Genetic deficiency of fructokinase is benign and often
detected incidentally when the urine is checked for
glucose with a dipstick
 Fructose 1-phosphate aldolase deficiency is a severe
disease because of accumulation of fructose 1-
phosphate in the liver and renal proximal tubules
 Symptoms are reversed after removing fructose and
sucrose from the diet
 Are cataracts part of the complications?

17.  Hereditary fructose intolerance is an autosomal recessive
disease (incidence of 1/20,000) due to a defect in the gene
that encodes aldolase B in fructose metabolism
 There is accumulation of fructose 1-phosphate in
hepatocytes and thereby sequestering of inorganic
phosphate in this substance
 Eventually, the liver becomes damaged due to the
accumulation of trapped fructose 1-phosphate
 Signs include lethargy, jaundice, vomiting, diarrhoea
Hereditary Fructose Intolerance