Mitsouras- Interconversion of sugars

Question 1

what is the primary site of fructose and galactose metabolism?

Answer 1

liver.

Question 2

what does sucrose break down too?

Answer 2

glucose and fructose

Question 3

what does lactose break down too?

Answer 3

glucose and galactose

Question 4

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

Answer 4

no

Question 5

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

Answer 5

GLUT5

Question 6

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

Answer 6

GLUT2

Question 7

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

Answer 7

fructokinase

Question 8

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

Answer 8

hexokinase

Question 9

does hexokinase have a higher affinity for glucose than fructose?

Answer 9

yes

Question 10

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

Answer 10

irreversible phosphorylation. 1 ATP is hydrolyzed

Question 11

what is the function of aldolase B?

Answer 11

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

Question 12

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

Answer 12

becomes an intermediate in glycolysis. isomerized by triose P isomerase

Question 13

what enzyme is needed to phosphorylate glyceraldehyde?

Answer 13

triose kinase

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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.

Question 16

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

Answer 16

glyceraldyhyde-3-phosphate

Question 17

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

Answer 17

Aldolase B (hereditary fructose intolerance)

Question 18

what are the three consequences of deficiency?

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

liver failure and death

Question 21

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

Answer 21

hypoglycemia and vomiting (decreased ATP synthesis)

Question 22

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

Answer 22

hyperuricemia

Question 23

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

Answer 23

hypodglycemia and hepatomegaly (glycgenolysis is inhibited)

Question 24

where is galactose mainly metabolized?

Answer 24

the liver

Question 25

is transport of galactose into cells insulin-dependent?

Answer 25

nope

Question 26

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

Answer 26

GLUT 1, 3

Question 27

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

Answer 27

GLUT2

Question 28

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

Answer 28

galactokinase

Question 29

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

Answer 29

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

Question 30

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

Answer 30

phosphoglucomutase is needed for isomerization

Question 31

why does UDP-glucose need to be regenerated?

Answer 31

it is a substrate for glycogenesis

Question 32

are glucose and galactose considere epimers?

Answer 32

yes. they are epimers at C-4

Question 33

how is UDP-galactose converted to UDP-glucose?

Answer 33

UDP-hexose-4-epimerase

Question 34

what is considered to be non-classical galactosemia?

Answer 34

glactokinase deficiency

Question 35

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

Answer 35

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

Question 36

what are symptoms of non-classical galactosemia?

Answer 36

galactosemia, galactosuria and cataracts

Question 37

what is galactosemia?

Answer 37

accumulation of galactose in the blood

Question 38

what is galactosuria?

Answer 38

accumulation of galactose in urine

Question 39

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

Answer 39

galactitol

Question 40

where else can galactitol accumulate and what are the consequences?

Answer 40

in the brain. this leads to mental retardation

Question 41

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

Answer 41

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

Question 42

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

Answer 42

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

Question 43

how is GALT deficiency manifested in new born babies?

Answer 43

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

Question 44

what enzyme converts monosaccharide into alcohols?

Answer 44

aldose reductase

Question 45

how is sorbitol converted to fructose?

Answer 45

sorbitol dehydrogenase

Question 46

where is sorbitol dehydrogenase present?

Answer 46

liver, ovaries, sperm and seminal vesicles

Question 47

what is the polyol pathway? and why is it important

Answer 47

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

Question 48

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

Answer 48

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

Question 49

is galactitol a substrate for sorbitol dehydrogenase?

Answer 49

nope. so galactitol will also accumulate in the cell

Question 50

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

Answer 50

lens=cataracts schwann cells= peripheral neuropathy kidney= nephropathy

Question 51

how does elevated galactose effect the lens and brain?

Answer 51

``` lens= cataracts brain= brain damage ```