Metabolism of Other Carbohydrates Flashcards
sucrose components
fructose + glucose
lactose components
glucose + galactose
maltose components
glucose + glucose
beta-fructosidase
breaks sucrose into fructose + glucose
SLGT1
symporter for glucose and galactose into cell
GLUT5
channel for fructose
How does fructose enter glycolysis to be metabolized to glucose?
fructose –> fructose-1-P (fructokinase) –> DHAP by aldolase-B –> DHAP can not enter the glycolysis pathway
essential fructosuria
fructokinase deficiency which results in high fructose levels in urine; no treatment needed
hereditary fructose intolerance
aldolase B deficiency (liver) which results in poor feeding, irritability, neonatal jaundice, vomiting, sleepiness, intolerance to fruit
What happens when you have an aldolase B deficiency?
inhibits glycolysis and gluconeogenesis and depletes the ATP pool; will lead to accumulation of fructose-1-P
inhibition of gluconeogenesis
leads to lactic acidosis
accumulation of fructose-1-P
depletes the ATP pool and leads to hyperuricemia (AMP converted to uric acid)
polyol (sorbitol) pathway
glucose –> sorbitol –> fructose
aldol reductase
glucose –> sorbitol
sorbitol dehydrogenase
sorbitol –> fructose
When is polyol pathway active?
at high glucose levels
What tissues express high levels of sorbitol dehydrogenase?
liver, ovaries, and seminal vesicles
increased polyol pathway causes _
osmotic and oxidative stress
Why does polyol pathway increase oxidative stress?
aldose reductase requires the conversion of NADPH into NADP+, depleting NADPH in the cell –> NADPH can not form glutathione which results in increased oxidative stress
increased sorbitol causes _
osmotic stress (cell edema) and decreased ATPase activity (NT delay)
symptoms of increased polyol pathway
chronic complications including neuropathy, retinopathy, and renal failure
tissues with low levels of sorbitol dehydrogenase are susceptible to _
high glucose levels leading to diabetic neuropathy and diabetic retinopathy (no sorbitol dehydrogenase)
primary lactose intolerance
lactase production decreases in adulthood
secondary lactose intolerance
lactase production decreases after an illness, injury, or small intestine surgery
tertiary lactose intolerance
congenital lactase deficiency
galactose is metabolized by the _
Leloir pathway
Leloir pathway
galactose –> galactose-1-P –> glucose-1-P
galactokinase (GALK)
galactose –> galactose-1-P
galactose 1-P uridylyltransferase (GALT)
galactose-1-P –> glucose-1-P; also converts UDP-glucose into UDP-galactose
galactosemia
results from defect in Leloir pathway
GALT deficiency
leads to type I galactosemia; most common form
GALK deficiency
leads to type II galactosemia
type II galactosemia treatment
galactose and lactose restricted diet, calcium supplements to maintain bone density
type II galactosemia symptoms
elevated galactose, cataracts due to increased galactitol
type I galactosemia symtpoms
failure to thrive, liver and renal dysfunction, cataracts, abnormal liver development, and sepsis
type I galactosemia treatment
low galactose and lactose diet
UDP-glucose-4-epimerase (GALE)
converts UDP-galactose to UDP-glucose to be made into glycogen
GALE deficiency
type III galactosemia
type III galactosemia symptoms
similar to GALT deficiency if severe form
type III galactosemia treatment
low galactose and lactose treatment
mild form of type III galactosemia
restricted to blood cells, asymptomatic
congenital disorders of glycosylation symptoms
low muscle tone, misaligned eyes, poor growth, developmental delay, liver disease, stroke-like episodes, seizures, abnormal bleeding/blood clotting
alpha-galactose syndrome
caused by an allergic response to glycoproteins (galactose-alpha-1,3-galactose in meat) causing rashes, hives, nausea, vomiting, breathing difficulty, low BP, dizziness, and stomach pain
xenobiotics are solubilized by _
conjugation to glucuronate for removal by liver
