Disaccharide metabolism

Question 1

What is the transferase used for fructose

Answer 1

GLUT5 (loads in the sperm)

Question 2

Galactose transferase

Answer 2

SGLT1 (with glucose)

Question 3

Is fructose or galactose metabolism faster?

Answer 3

Fructose metabolism is faster because it bypasses the rate limiting step of glycolysis…..bypasses PFK-1 and enters at G3P (3C) step where galactose eneters at Glu-6-P

Question 4

RLS in galactose metabolism

Answer 4

GALT (glucose 1p uridyltransferase)…needs UDP-glucose

Question 5

Sorbitol accumulation

Answer 5

glucose is reduced to sorbitol and oxidized to fructose; cells that lack the ability to do so (sorbitol dehydrogenase) will accumulate sorbitol which triggers water influx and causes swelling…..causes CATARACTS and peripheral neuropathy

Question 6

galactokinase deficiency

Answer 6

lead to accumulation of galactose and galactitol in blood and urine
• Accumulation of galactitol in lens of eye leads to JUVENILE CATARACTS in early infancy

Question 7

galactosemia

Answer 7

deficiency in glucose 1P uridyltransferase (GALT), leads to the accumulation of galactitol
• Liver failure, sepsis, bleeding, failure to thrive

Question 8

High fructose corn syrup and obesity

Answer 8

• Easier to convert to fat because it bypasses PFK-1n in glycolysis
• Might correlate with obesity since HFCS has increased 4000% since 70s.
ii. Galactosemia

Question 9

Galactosemia

Answer 9

• Classic: Conversion of galactose to glucose-1-P is prevented due to GALT deficiency (RLS)
• Failure to thrive, liver failure, sepsis, and bleeding
• Milder 5-25% in RBCs
• NonClassic or galactokinase deficiency: galactokinase deficiency so galactose cant be phosphorylated
• BOTH result in cataracts due to galactitol accumulation