Fructose and Galactose Metabolism

Question 1

describe two GluT transporters than transfer fructose

Answer 1

GluT 2 and GluT 5

Question 2

Glut 5

Answer 2

major fructose transporter

• found on apical side of small intestines, sperm cells
• relatively low Km (Km = 1 mM)

Question 3

when fructose enters the cell, it gets phosphorylated. Describe the easy way

Answer 3

fructose can get phosphorylated by hexokinase to fructose 6 P which is an intermediate in the glycolytic pathway and all is good. BUT this Km is really high for fructose and low for glucose…

Question 4

What enzyme phosphorylates fructose on C-1

Answer 4

Fructokinase

Question 5

after fructose is phosphorylated by fructokinase to make fructose 1-P, what enzyme acts next?

Answer 5

Aldolase B

Question 6

aldolase B cleaves fructose 1-P to form

Answer 6

glyceraldehyde and dihydroxyacetone phosphate

Question 7

glyceraldehyde is converted to glyceraldehyde 3-P by

Answer 7

triose kinase

Question 8

Essential fructosuria

Answer 8

• lack of fructokinase
• autosomal recessive
• benign condition and fructose accumulates in the urine

Question 9

hereditary fructose intolerance

Answer 9

• autosomal recessive
• absence of aldolase B which means fructose 1 P is trapped in the cell with no way to move forward and no way to get out
• clinical features: severe hypoglycemia, vomiting, jaundice, hemorrhage, hepatomegaly, renal dysfunction, hyperuricemia, and lacticacidemia
• NEED TO CUT OUT ALL FRUCTOSE and sucrose from diet

Question 10

what enzymes phosporylates galactose on C 1

Answer 10

galactokinase

Question 11

Galactose 1-P is converted to UDP-galactose by

Answer 11

Gal 1‐P uridyltransferase

Question 12

UDP‐hexose 4‐epimerase converts UDP‐gal to

_____

Answer 12

UDP‐glu.

Question 13

Galactokinase deficiency

Answer 13

• rare autosomal recessive disorder
• galactosemia and galactosuria
• if galactose is consumed then galactitol accumulates

Question 14

elevated galactitols can cause ____

Answer 14

cataracts

Question 15

classic galactosemia

Answer 15

• due to GALT deficiency
• autosomal recessive
• clinical presentation: vomiting, diarrhea, jaundice, galactosemia, and galctoseuria
• accumulation of galactose 1-P and galactitol in nerve, lens, liver, kidney, can cause liver damage, cataracts, and severe mental retardation

Question 16

whats Prolactin’s role in lactose production?

Answer 16

-prolactin stimulates the expression of protein B (α‐lactalbumin) changing substrate specificity of the transferase which then allows it to catalyze the formation of lactose from UDP galactose and glucose