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MCB II Block 2 > non-glucose sugars and pentose shunt > Flashcards

non-glucose sugars and pentose shunt Flashcards

1
Q

how do we trap galactose inside cell

A

phosphorylate

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2
Q

how do we trap fructose inside cell

A

phosphorylate

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3
Q

how do we trap glucose inside cell

A

phosphorylate

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4
Q

hepatocytes have what transporter

A

GLUT2

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5
Q

fructose comes from

A

sucrose

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6
Q

aldolaes B is found in

A

liver

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7
Q

is fructose 1-P an intermediate in glycolysis

A

no

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8
Q

in liver, how is aldolase b used

A

backwards. so when pts fasting the liver will have problems

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9
Q

if there is deficiency of aldolase b what disease

A

hereditary fructose intolerance

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10
Q

pts who have hereditary fructose intolerance, what symptoms

A

Hypoglycaemia, and lactic acidosemia, vomiting, haemorrhage, hepatomegaly, renal dysfunction, hyperuricaemia, lacticacidaemia, cataracts

esp. when pt is fasting

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11
Q

how is hereditary fructose intolerance treated

A

dietary restriction of fructose, sucrose and sorbitol

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12
Q

fructose metabolism takes place primarily where

A

in liver

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13
Q

in fructose metabolism, what is rate limiting step

A

aldolase b

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14
Q

soribitol pathway, what is function

A

synthesis of fructose from glucose via sorbitol

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15
Q

in sorbitol pathway glucose is reduced to sorbitol by

A

aldose reductase

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16
Q

in sorbitol pathway sorbitol is oxidised to fructose by

A

sorbitol dehydrogenase

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17
Q

where is sorbitol pathway esp. used

A

in seminal vesicles (sperm need fructose!)

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18
Q

sorbitol

A

cannot leave cell, there is no transporter for it

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19
Q

can sorbitol ever leave the cell

A

no

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20
Q

if there is a lot of glucose, the cell will accumulate a lot of

A

sorbitol

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21
Q

describe what happens in eye regarding sorbitol

A

there is a lot of glucose b/c it needs a lot of it for energy. aldose reductase is active but soribtol dehydrogenase has lower activity - it can accumulate soribotl. if there is too much glucose then too much soribtol and cause damage to eye.

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22
Q

what is function of aldose reductase

A

glucose →sorbitol

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23
Q

what is function of sorbitol dehydrogenase

A

sorbitol → fructose

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24
Q

go through mechanism of fructose-induced cataracts

A

pg 10

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25
Q

obesity endemic takes off b/c of

A

high fructose corn syrup (among other things)

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26
Q

fructose goes to cells and is trapped in cells as

A

fructose 1 phosphate

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27
Q

describe how high fructose corn syrup causes obesity

A

fructose 1 phosphate, fructose metabolism, so you bipass the PFK step which is major regulatory step in glycolysis, since we bipass the regulatory step then we don’t have regulation of glycolysis. we don’t regulate pyruvate, and pyruvate can be turned into fat.

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28
Q

glucose and galactose are

A

epimers

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29
Q

galactose 1-P is utilized by what enzyme

A

galactose 1-phosphate uridyltransferase

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30
Q

draw out galactose 1-P and UDP glucose reaction

A

pg 12 (just do the important step)

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31
Q

galactose kinase deficiency

A

if galactose doesn’t stay in cell, blood gets flooded with galactose and have galactose hyperanemia. this could cause lenses to get clouded or cataracts.

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32
Q

galactose uptake is independent of what

A

insulin

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33
Q

in intestine lactase hydrolysise lactose to yield

A

glucose & galactose by breaking ß-1,4 linkage

34
Q

show galactose to galactose 1-P step

A

pg 12

35
Q

Classical galactosaemia (GALT deficiency) can lead to

A

cataracts

36
Q

how can lactose intolerant mother breastfeed

A

mom produces galactosyltransferase, when she has baby then protein B (lactalbumin) will catalyse condensation of glucose and galactose to make lactose

37
Q

what pathway is essential ina ll cells to provide NADPH for reductive detoxification

A

pentose phosphate pathway

38
Q

what is pentose phosphate pathway used for

A

Pathway essential in all cells to provide NADPH for reductive detoxification and in most cells to provide ribose 5-P for nucleotide synthesis

39
Q

bottom line of pentose phosphate pathway

A

NADPH is used

40
Q

why is NADPH needed

A

synthesis (cholesterol, fatty acids, hormones)

anabolism

41
Q

ribose 5-P is precuroser of

A

nucleic acids

42
Q

what is needed in rapidly dividing cells

A

pentose phosphate pathway

43
Q

give general summary of pentose pathway

A

oxidative reaction makaes NADPH

nonoxidative pathway makes ribose 5P

44
Q

the oxidative phase of pentose pathway produces

A

NADPH and pentose

45
Q

transketolase is enzyme that does what

A

Transketolase transfers a 2-C fragment from xylulose 5-P releasing glyceraldehyde 3-P
pg 23

46
Q

transketolase needs what

A

thiamine -PP (a vitamin)

47
Q

thiamine PP is a

A

vitamin

48
Q

NADPH in RBC is used to do what

A

RBC are exposed to oxidative stress.

NADPH is needed to make sure H2O2 won’t harm the cell

49
Q

what produces NADPH

A

pentose phosphate pathway

50
Q

draw out mechanism for how NADPH allows RBC to avoid oxidative stress

A

pg 26

51
Q

what are the precipitating factors of G6PD deficiency

A

oxidant drugs
favism
infection

52
Q

UDP-sugars are what form of sugar

A

activated

53
Q

where is UDP glucose formed

A

glycogen synthesis pathway

54
Q

where would mutation be in classical galactosemia?

A

draw out, see pg 14

55
Q

where would mutation be in nonclassical galactosemia

A

draw out, see pg 14

56
Q

if galactitol is converted by aldose reductase what can happen in infants

A

cataracts

57
Q

what happens if ribose 5p has been produced but isn’t needed for nucleotide synthesis

A

it’s converted to glycolytic intermediates

58
Q

if cell needs NADPH, what does it do to fructose 6-P

A

converts it to glucose 6-P

59
Q

the conversion of glycolytic intermediates to ribose 5-P is what kind of reaction

A

reversible

60
Q

if cell has enough NADPH but needs ribose 5-P what does it do

A

inhibits oxidative path. ribose 5-P synthesized from glycolytic intermediates

61
Q

what is NADPH’s role in regulating pentose phosphate pathway

A

When NADPH is forming faster than it is being used for biosynthesis and glutathione reduction, [NADPH] rises and inhibits the first enzyme in the pentose phosphate pathway.

As a result, more glucose 6-phosphate is available for glycolysis. (pg 22)

62
Q

do RBCs generate NADPH?

A

no

63
Q

why is NADPH used instead of NADH in reductive rxns requiring input of electrons

A

because NADPH/NADP+ ratio&raquo_space; NADH/NAD+

NADH rapidly oxidised back to NAD+ by ETC so [NADH] is low

64
Q

look at G6PD deficiency slide and understand generally

A

pg 27

65
Q

what is a key component of antioxidant defences

A

glutathione

66
Q

what is the major antioxidant in the fluid lining the bronchial epithelium

A

glutathione

67
Q

draw glutathione reductase reaction

A

pg 28

68
Q

lactose is made out of

A

glucose & galactose

69
Q

sucrose is made out of

A

glucose & fructose

70
Q

what happens to disaccharides to be of use in glycolysis

A

they are hydrolyzed

71
Q

what can convert to G6P

A

glucose, fructose, galactose, mannose

72
Q

name five different fates of G6P in the liver

A

Dephosphorylate to yield free glucose to send to other tissues
Make into liver glycogen
Enter glycolysis, make acetyl CoA and then ATP for hepatocytes themselves
Enter glycolysis, make acetyl CoA to be made into fatty acids and then TAGs
Enter pentose phosphate pathway to yield NADPH and ribose-5-phosphate

73
Q

what transporter in hepatocytes allows the passive diffusion of glucose

A

GLUT2 transporter

74
Q

hepatocytes don’t have hexokinase, they have

A

glucokinase

75
Q

what is difference b/w glucokinase and hexokinase

A

glucokinase has higher km (g6p isn’t made when glucose is low)
glucokinase isn’t inhibited by g6p, so it will just keep being made to g6p

76
Q

draw the two rate limiting steps in fructose metabolism

A

pg 6

77
Q

what does fructose metabolism generate that is an intermediate of glycolysis

A

glyceraldehyde 3-P & DHAP

78
Q

how does fructose enter epithelial cells

A

GLUT5

79
Q

GLUT5 is

A

insulin independent

80
Q

what happens to fructose when it enters epithelial cells

A

it is rapidly phosphorylated to fructose 1 phosphate by fructokinase

81
Q

if there is a deficiency in fructokinase, what disease

A

Essential Fructosuria

82
Q

if there is fructose malabsorption, it will affect what

A

affects uptake of tryptophan resulting in deficiency of melatonin & serotonin.

MCB II Block 2 (10 decks)

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