HANDOUT: OTHER PATHWAYS OF SUGAR METABOLISM Flashcards
What are the other pathways of sugar metabolism?
Pentose phosphate pathway
Fructose metabolism
galactose metabolism
Synthesis of Glycosides, Lactose, glycolipids and glycoproteins
Where can fructokinase be seen?
Liver
Intestine
Kidney
What is the function of fructokinase?
facilitate phosphorylation from fructose to F1P
Fructokinase vs Glucokinase
Fructokinase:
- doesn’t act on glucose
- Not insulin-dependent
Fructose-1-phosphate is cleaved into ________ by __________.
DHAP and Glyceraldehyde by aldolase B.
Why can fructose flood the pathways in the liver?
Because it bypasses PFK1 regulatory enzyme, therefore fructose undergo rapid glycolysis thus the permission to flood the liver.
What will the flooding of fructose in the liver lead to?
increased FA synthesis
Increased. FA esterification
increased VLDL
increased TAG
increased LDL
What can be synthesized from Polyol pathway?
Fructose
What step is the polyol pathway?
This is the first step wherein the sugar is reduced into sugar alcohol (i.e. Glucose to sugar alcohol sorbitol)
What facilitates the conversion of sugar into sugar alcohol in the polyol pathway?
Aldose reductase
Where can polyol pathway be found and what is its function there?
Seminal vesicles –> produce fructose for seminal fluid
How do spermatozoa use fructose?
major fuel source when in seminal fluid.
It will switch into glucose when in the female reproduct tract.
Enumerate the process of polyol pathway from glucose to fructose
Glucose –> (reduced)sorbitol –> (oxidize) fructose
How is aldose reductase activity harmful in the eye?
It is in the eye where alcohols are synthesized:
Glucose –> sorbitol
Galactose –> Galactitol
Therefore, increased blood glucose or galactose concentration would lead to higher synthesis than they are removed.
EFFECT: High osmotic pressure within the lens
What is deficient in essential fructosuria?
Fructokinase
What is essential fructosuria?
- Benign condition.
- fructokinase deficiency.
- fructose can’t be taken up by liver cells
- fructose shows up in liver & blood. Therefore have high levels of fructose there.
- eventually, 90% of fructose is metabolized (which is likely due to alternative pathways).
What is deficient in fructose intolerance?
fructose 1-Phosphate aldolase
What accumulates in fructose intolerance?
fructose-1-phosphate
(since it wasn’t cleaved)
Describe fructose intolerance
This is dietary. There’s just so much fructose our body can metabolize. Hence, this is malabsorption., wherein fructose is not metabolized.
There’s a severe hypoglycemia in the patient. In young children, this is due to prolonged fructose ingestion which may lead to death
What is deficient in hereditary fructose intolerance?
Fructose-1-phosphate alsolase (aldolase B)
What accumulates in hereditary fructose intolerance?
fructose-1-phosphate
describe hereditary fructose intolerenace
F1P accumulates due to deficiency in Aldolase B. With that, the available Phosphate enzyme decreases, inhibiting gluconeogenesis and glycogenolysis. Therefore, patient will be hypoglycemic. Also, these accumulations may lead to enzymes blocking the tissue.
What damages can hereditary fructose intolerance bring about?
- enzyme block damage –> accum of F1P in tissues –> liver damage, Jaundice —> cirrhosis, ascites.
- can also result to renal tubular damage
- hypoglycemia
How much galactose per kg can infants ingest?
1g of glucose per kg
(can metabolize more than adults can)
