Transcript Galactose

Galactose
Galactose (Gal)
• Galactose
• Type of sugar found
– In dairy products
– Sugar beets
– Mucilages
• It can be found in the
body
– Glycolipids
– Glycoproteins
• sweetener
Galactose (Gal)
• Disaccharide lactose
– Galactose
– Glucose
• Hydrolysis of lactose to
glucose and galactose
– Lactase
• In the human body,
glucose is changed into
galactose in order to
enable the mammary
glands to secrete
lactose.
Galactose (Gal)
• Blindness is due to
the conversion of
circulating
galactose to the
sugar alcohol
galacitol, by an
NADPH-dependent
galactose reductase
that is present in
neural tissue and in
the lens of the eye.
Absorption of glucose, galactose – Na+
cotransport
Intestinal epithel cells
Capillary
Lumen
GluT2
Glu, Gal
Glu, Gal
SGLT
K+,Na+-ATP-ase
Na+
Na+
ADP + Pi
Na+
ATP
Fructose
Fructose
GluT5
SGLT – sodium-glucose transporter
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Lactose intolerance
• the inability to metabolize lactose, a sugar found
in milk and other dairy products
• 75% of adults worldwide show some decrease in
lactase activity during adulthood
• The frequency of decreased lactase activity
ranges from as little as 5% in northern Europe,
up to 71% for Southern Europe, to more than
90% in some African and Asian countries
Lactose intolerance
• Disaccharides cannot be absorbed
through the wall of the small intestine
• lactose present in ingested dairy products
remains uncleaved and passes intact into
the colon.
• enteric bacteria
– in vivo fermentation produces copious
amounts of gas (a mixture of hydrogen,
carbon dioxide, and methane).
Primary lactose intolerance.
• Environmentally induced when weaning a
child in non-dairy consuming societies
• This is found in many Asian and African
cultures, where industrialized and
commercial dairy products are uncommon.
Secondary lactose intolerance.
• resulting from certain gastrointestinal diseases
• including exposure to intestinal parasites such
as giardia
• such cases the production of lactase may be
permanently disrupted
• A very common cause of temporary lactose
intolerance is gastroenteritis, particularly when
the gastroenteritis is caused by rotavirus.
• Another form of temporary lactose intolerance is
lactose overload in infants.
Congenital lactase deficiency.
• A genetic disorder which prevents
enzymatic production of lactase.
• Present at birth, and diagnosed in early
infancy.
Lactase activity
• The normal mammalian condition is for the
young of a species to experience reduced
lactase production at the end of the
weaning period
– (a species-specific length of time).
• In non dairy consuming societies, lactase
production usually drops about 90% during
the first four years of life, although the
exact drop over time varies widely.
Lactase activity
• a mutation on chromosome 2 which
eliminates the shutdown in lactase
production,
• making it possible for members of these
populations to continue consumption of
fresh milk and other dairy products
throughout their lives without difficulty.
Lactase activity
• This appears to be an evolutionarily recent
adaptation to dairy consumption, and has
occurred independently in both northern
Europe and east Africa in populations with
a historically pastoral lifestyle.
• Lactase persistence, allowing lactose
digestion to continue into adulthood, is a
dominant allele, making lactose
intolerance a recessive genetic trait.
Glucose-galactose malabsorption
• generally becomes apparent in the first
few weeks of a baby's life.
• Affected infants experience severe
diarrhea resulting in
– life-threatening dehydration,
– increased acidity of the blood and tissues
(acidosis),
– weight loss when fed breast milk or regular
infant formulas.
Glucose-galactose malabsorption
• However, they are able to digest fructosebased formulas that do not contain
glucose or galactose.
• Some affected children are better able to
tolerate glucose and galactose as they get
older.
Glucose-galactose malabsorption
• is a rare disorder;
• only a few hundred cases have been identified
worldwide.
• 10 percent of the population may have a
somewhat reduced capacity for glucose
absorption without associated health problems.
• This condition may be a milder variation of
glucose-galactose malabsorption.
• This condition is inherited in an autosomal
recessive pattern
galactokinase (GALK)
galactose-1-phosphate
uridyltransferase (GALT)
uridine diphosphate galactose 4'-epimerase (GALE)
Clinical Significances of
Galactose Metabolism
•
Three inherited disorders of
galactose metabolism have
been delineated.
– loss of the enzyme galactose-1phosphate uridyl transferase
– loss of the enzyme
galactokinase
• Vomiting and diarrhea occur
following ingestion of milk,
hence individuals are termed
lactose intolerant.
• impaired liver function (severe
cirrhosis),
• elevated blood galactose,
• hypergalactosemia,
• hyperchloremic metabolic
acidosis,
• urinary galactitol excretion
• hyperaminoaciduria.
Clinical Significances of
Galactose Metabolism
• Unless controlled by
exclusion of
galactose from the
diet, these
galactosemias can
go on to produce
blindness and fatal
liver damage.
Clinical Significances of
Galactose Metabolism
• The third disorder of
galactose metabolism result
from a deficiency of UDPgalactose-4-epimerase.
• Two different forms of this
deficiency have been found.
– One is benign affecting only
red and white blood cells.
– The other affects multiple
tissues and manifests
symptoms similar to the
transferase deficiency.
• Treatment involves
restriction of dietary
galactose.
Lactose Synthesis