Covers the metabolism of galactose, fructose and mannose, taking galactose through uptake, phosphorylation, and conversion to UDP-glucose and glycogen or glycolysis, then fructose cleavage into glycolytic intermediates and mannose isomerisation to fructose-6-phosphate and GDP-mannose. It then describes galactosemia types I and II, essential fructosuria and fructose intolerance, with their deficient enzymes, symptoms and dietary management, and ends with four multiple-choice questions and answers.
Topic 22 of 70 in the MU Sofia syllabus for Biochemistry (Dental Medicine, Year 2). The free AceMed note covers it in 11 sections, about 640 words (5 min of reading), with 10 flashcards.
In this note
METABOLISM OF GALACTOSE(LIVER)
Metabolism of Galactose
Fructose Metabolism
Metabolism of Fructose:
Metabolism of Mannose:
Galactosemia:
GALACTOSEMIA
Essential Fructosuria:
Fructose Intolerance:
MCQs ☺
Answers
Metabolism of Galactose
1. Galactose Uptake and Activation:
Galactose is taken up into cells primarily via the sodium-dependent glucose transporter (SGLT1) or facilitated diffusion through glucose transporters.
Inside the cell, galactose is phosphorylated to galactose-1-phosphate by the enzyme galactokinase, utilizing ATP.
Metabolism of Galactose
2. Conversion of Galactose-1-phosphate to Glucose-1-phosphate:
Galactose-1-phosphate is converted to glucose-1-phosphate by the enzyme galactose-1-phosphate uridylyltransferase (GALT).
GALT catalyzes the transfer of a UDP (uridine diphosphate) to galactose-1-phosphate, forming UDP-galactose and glucose-1-phosphate.
Metabolism of Galactose
3. Conversion of UDP-Galactose to UDP-Glucose:
UDP-galactose is converted to UDP-glucose by the enzyme UDP-galactose 4-epimerase.
This enzyme catalyzes the epimerization of the C4 hydroxyl group of UDP-galactose to a C4 hydroxyl group, forming UDP-glucose.
Metabolism of Galactose
4. Incorporation of Glucose-1-Phosphate into Glycogen or Glycolysis:
Glucose-1-phosphate generated from galactose metabolism can be incorporated into glycogen synthesis via the enzyme glycogen synthase.
Alternatively, glucose-1-phosphate can enter glycolysis after conversion to glucose-6-phosphate by the enzyme phosphoglucomutase.
Metabolism of Fructose:
1. Fructose Uptake and Activation:
Fructose is transported into cells via the glucose transporter GLUT5.
Inside the cell, fructose is phosphorylated to fructose-1-phosphate by fructokinase, utilizing ATP.
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