Metabolism of saccharides Flashcards
1
Q
Galactose
A
- makes lactose
- structural component for carbohydrates
- energy source
- not insulin dependent
- metabolism is 2 steps to UDP-galactose
2
Q
Fructose
A
- found in sucrose
- energy source
- 10% of calories in western diet
- transported by GLUC-5
- not insulin dependent
- does not promote insulin
- bypasses PFK-1 so metabolizes more rapidly than glucose
3
Q
Fructokinase
A
- enzyme used in phosphorylation of fructose
- only found in liver, kidney, and small mucosal cells in intestine
- uses ATP
- IRREVERSIBLE
- makes 1P
4
Q
Hexokinase
A
- enzyme used in phophorylation of fructose(lower affinity than for glucose)
- acts in all other tissues
- makes 1-6bisP
5
Q
Aldolase B
A
- lots of aldolases can cleave fructose 1-6BisP
- ONLY aldolase B can cleave fructose 1P
6
Q
Products from Cleavage of fructose 1P
A
- DHAP can directly enter glycolysis
- Glyceraldehyde: can be phosphorylated to glyceraldehyde 3P and enter glycolysis or gluconeogenesis
- glyceraldehyde can also be converted to glycerol of TAG synthesis
7
Q
Aldose reductase
A
- found in eyes, schwann cells of peripheral nerves, liver, kidney,ovaries and seminal cells
- converts glucose to sorbitol
- does not matter in galactose metabolism, until galactose levels are high
8
Q
Sorbitol dehydrogenase
A
- only found in liver(metabolize sorbitol in diet)
- ovaries and seminal vesicles(energy source)
- sorbitol to frutose
9
Q
Conversion of glucose to sorbitol to fructose
A
-tissues that only make aldose reductase, will be damaged by longterm elevation of blood glucose (build up of sorbitol)
10
Q
Sorbitol accumulation
A
- sorbitol build up leads to osmotic uptake of water
- cataracts, retinopathy, nephropathy in diabetics
11
Q
Mannose
A
- C-2 epimer of glucose
- very little in diet(mostly synthesized by fructose)
- important component of glycoproteins
- substrate for hexokinase
- substrate for phosphomannoseisomerase to convert is to fructose 6P
12
Q
Lack of fructokinase
A
- fructosuria
- autosoma recessive
- 1:130,000 births
- benign condition
- fructose accumulates in urine
- just dont eat fructose…
13
Q
Fructose Poisoning
A
- autosomal recessive
- 1:20,000 births
- lack aldolase B and results in intracellular trapping of fructose 1P
- hypoglycemia, jaundice, hepatic failure
- remove sucrose and fructose from diet
- phosphates can’t make ATP so high AMP leads to hyperuricemia
14
Q
Galactokinase
A
- phosphorylation of galactose
- makes galactose 1P
15
Q
What is the difference between galactose and glucose?
A
-position of hydroxyl group
