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MCBM Part 1 > Mitsouras- Interconversion of sugars > Flashcards

Mitsouras- Interconversion of sugars Flashcards

1
Q

what is the primary site of fructose and galactose metabolism?

A

liver.

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2
Q

what does sucrose break down too?

A

glucose and fructose

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3
Q

what does lactose break down too?

A

glucose and galactose

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4
Q

does dietary fructose stimulate insulin release and is it dependent on insulin for transport into the cells?

A

no

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5
Q

what has a high affinity for fructose in SI, sperm, kidney, brain, muscle and adipocytes?

A

GLUT5

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6
Q

what has a high capacity for glucose, fructose, galactose in the liver, SI and kidney?

A

GLUT2

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7
Q

what kinase is found in the liver, kidney and SI?

A

fructokinase

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8
Q

what phosphorylates glucose and fructose and is found in all cells?

A

hexokinase

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9
Q

does hexokinase have a higher affinity for glucose than fructose?

A

yes

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10
Q

what kind of process is the phosphorylation by fructokinase and how many ATP does it require?

A

irreversible phosphorylation. 1 ATP is hydrolyzed

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11
Q

what is the function of aldolase B?

A

it cleaves Fructose 1-phosphate into glyceraldehyde and dihyroxyacetone phospate?

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12
Q

what does dihydroxyacetone phosphate proceed to do once it is produced?

A

becomes an intermediate in glycolysis. isomerized by triose P isomerase

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13
Q

what enzyme is needed to phosphorylate glyceraldehyde?

A

triose kinase

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14
Q

the metabolism of fructose is known to be much faster than the metabolism of glucose. why is that?

A

because the PFK-1 (rate limiting step) is bypassed.

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15
Q

what conditions have to be met in order for hexokinase to metabolize fructose?

A

since hexokinase has a lower affinity for fructose than it does for glucose, the intracellular concentration of fructose would need to be greater than glucose.

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16
Q

what is known to be a glycolytic intermediate and substrate for gluconeogenesis?

A

glyceraldyhyde-3-phosphate

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17
Q

deficiency of which enzyme (Fructokinase or Aldolase B) is considered to be more severe?

A

Aldolase B (hereditary fructose intolerance)

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18
Q

what are the three consequences of deficiency?

A

accumulation of rxn substrate, substrate redirected to other linked pathways and end-products of pathway missing

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19
Q

if a person has fructokinase defiency can they still metabolize fructose?

A

yes. Hexokinase (extra-hepatic) metabolism of fructose is intact

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20
Q

if fructose intolerance goes on untreated, what are the consequences?

A

liver failure and death

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21
Q

what clinical symptoms would a patient experience if Fructose-1-P accumulates in the liver?

A

hypoglycemia and vomiting (decreased ATP synthesis)

22
Q

what clinical symptoms would a patient experience with increased AMP levels?

A

hyperuricemia

23
Q

what clinical symptoms would a patient experience with AMP allosterically inhibiting glycogen phosphorylase?

A

hypodglycemia and hepatomegaly (glycgenolysis is inhibited)

24
Q

where is galactose mainly metabolized?

A

the liver

25
Q

is transport of galactose into cells insulin-dependent?

A

nope

26
Q

what has high affinity for glucose and galactose in the brain, RBCs and others?

A

GLUT 1, 3

27
Q

what has high capacity for glucose, fructose, galactose in the liver SI and kidney?

A

GLUT2

28
Q

what enzyme is needed to produce galactose-1-phosphate?

A

galactokinase

29
Q

what is needed to convert galactose-1P to glucose-1P?

A

UDP-glucose is used as donor for exchange by galactose-1-P-uridyl transferase (GALT)

30
Q

how do we get glucose-6P from glucose-1P?

A

phosphoglucomutase is needed for isomerization

31
Q

why does UDP-glucose need to be regenerated?

A

it is a substrate for glycogenesis

32
Q

are glucose and galactose considere epimers?

A

yes. they are epimers at C-4

33
Q

how is UDP-galactose converted to UDP-glucose?

A

UDP-hexose-4-epimerase

34
Q

what is considered to be non-classical galactosemia?

A

glactokinase deficiency

35
Q

what are the symptoms if a patient has galactose-1-P uridyltransferase deficiency?

A

(classical glactosemia) cataracts, liver damage, mental retardation, jaundice, lethargy, hypotonia, glactosuria and galactosemia

36
Q

what are symptoms of non-classical galactosemia?

A

galactosemia, galactosuria and cataracts

37
Q

what is galactosemia?

A

accumulation of galactose in the blood

38
Q

what is galactosuria?

A

accumulation of galactose in urine

39
Q

what product of galactose metabolism by aldose reductase in known to accumulate in the eye and cause cataracts?

A

galactitol

40
Q

where else can galactitol accumulate and what are the consequences?

A

in the brain. this leads to mental retardation

41
Q

what two by-products of galactose are known to accumalate in the brain and cause mental retardation?

A

galactitiol and galactose 1-P (also causes liver damage)

42
Q

what are all the clinical signs of GALT deficiency (classical galactosemia)?

A

galactosuria, galactosemia, cataracts, liver damage, mental retardation, jaundice, lethargy and hypotonia

43
Q

how is GALT deficiency manifested in new born babies?

A

feeding on breast milk (lactose). remember that lactose is broken down to glucose and galactose

44
Q

what enzyme converts monosaccharide into alcohols?

A

aldose reductase

45
Q

how is sorbitol converted to fructose?

A

sorbitol dehydrogenase

46
Q

where is sorbitol dehydrogenase present?

A

liver, ovaries, sperm and seminal vesicles

47
Q

what is the polyol pathway? and why is it important

A

converting sugars to alcohols in cells. important if glucose and galactose levels are elevated

48
Q

if sorbitol dehydrogenase is not present in a cell, what will happen to the sorbitol in that cell?

A

it will accumulate and the cell will swell (has osmotic effect)

49
Q

is galactitol a substrate for sorbitol dehydrogenase?

A

nope. so galactitol will also accumulate in the cell

50
Q

individuals with hyperglycemia (diabetes mellitus) will have what symptoms in the lens, schwann cells of peripheral nerves and kidney?

A

lens=cataracts
schwann cells= peripheral neuropathy
kidney= nephropathy

51
Q

how does elevated galactose effect the lens and brain?

A 
lens= cataracts
brain= brain damage

MCBM Part 1 (29 decks)

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