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Biochemistry > PPP > Flashcards

PPP Flashcards

1
Q

What are major functions of PPP?

A
  • formation of NADPH for synthesis of FAs and steroids and maintaining reduced glutathione for antioxidant activity
  • synthesis of RIBOSE for nucleotide, nuclei acid formation
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2
Q

what are the main hexoses absorbed from GI tract?

A

glucose, fructose, galactose

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3
Q

What will fructose and galactose be converted into in the liver?

A

Glucose

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4
Q

glucose-6-phosphate dehydrogenase deficiency

A

Acute hemolysis of RBC = hemolytic anemia

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5
Q

In the PPP, what is used as hydrogen acceptor IOT achieve oxidation?

A

NADP+

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6
Q

What enzyme catalyzes the dehydrogenation of G6P to 6-phosphogluconalactone?

A

G6P dehydrogenase

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7
Q

What enzyme hydrolyzes 6-phosphogluconalactone?

A

gluconalactone hydrolase

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8
Q

What catalyzes the 2nd oxidative step of PPP?

A

6-phosphogluconate dehydrogenase

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9
Q

What enzyme catalyzes the reduction of cortisone (inactive) to cortisol (active) in liver, NS, & adipose tissue?

A

11-b-hydroxysteroid dehydrogenase-1

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10
Q

What increases xylulose excretion?

A

aminopyrine and antipyrine

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11
Q

What can high oral doses of fructose cause?

A

osmotic diarrhea

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12
Q

What causes hereditary fructose intolerance?

A

Absence of aldose B

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13
Q

how is glucuronic acid synthesized from glucose?

A

uronic acid pathway

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14
Q

what is the importance of glucuronic acid?

A

conjugation & excretion of metabolites & foreign chemicals as glucuronides; largely responsible for elimination of poisonous substances

highly soluble compound that can bind to substances such as hormones, drugs, & toxins to facilitate their transport around body

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15
Q

In PPP, 3 molecules of glucose give rise to ?

A

3 molecules of CO2

3 5-carbon sugars

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16
Q

2 molecules of _______ will regenerate G6P

A

glyceraldehyde-3-phosphate

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17
Q

reactions of PPP occur in?

A

cytosol

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18
Q

what 2 phases does PPP go through?

A
  • irreversible oxidative phase

- reversible nonoxidative phase

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19
Q

What happens in the first phase of PPP?

A

G6P is dehydrogenated & decarboxylated to form a pentose, ribulose-5-phosphate

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20
Q

what happens in the 2nd phase?

A

ribulose-5-phosphate is converted back to G6P by a series of rxns involving TRANSKETOLASE and TRANSALDOLASE.

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21
Q

What enzyme catalyzes first oxidative step in PPP? (1st)

A

glucose-6-phosphate dehydrogenase

(NADP+ used —> NADPH)

(enzyme oxidized G6P to 6-phosphogluconalactone)

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22
Q

What happens after G6P is oxidized to 6-phosphogluconalactone? What enzyme is at work? (2nd)

A

6-phosphogluconalactone is hydrolyzed to 6-phosphogluconate by the enzyme GLUCONALACTONE HYDROLASE

23
Q

What happens after 6-phosphogluconalactone is hydrolyzed to 6-phosphogluconate? What enzyme is in play? (3rd)

A

6-phosphogluconate is decarboxylated to ribulose-5-phosphate

by the enzyme 6-phosphogluconate dehydrogenase.

this is also the 2nd oxidative process in PPP

(NADP+ used –> NADPH)

24
Q

what are the 2 NADP-dependent enzymes in PPP?

A

glucose-6-phosphate dehydrogenase

6-phosphogluconate dehydrogenase

25
Q

In ER, what is hexose-6-phosphate dehydrogenase? what does it do?

A
  • isoenzyme of G6P dehydrogenase

- provides NADPH for hydroxylation rxns and also for 11-B-hydroxysteroid dehydrogenase-1

26
Q

the non-oxidative phase of PPP generates?

A

ribose precursors

27
Q

what happens after decarboxylation to ribulose-5-phosphate?

A

2 products are made

  1. ribulose-5-phosphate is converted to the epimer xylulose-5-phosphate (ketopentose) via EPIMERASE
  2. ribulose-5-phosphate is converted to ribose-5-phosphate (aldopentose) via RIBOSE-5-PHOSPHATE KETOISOMERASE
28
Q

what is used for nucleotide and nucleic acid synthesis?

A

ribose-5-phosphate

29
Q

transfers 2-carbon unit comprising carbons 1 & 2 of a ketose onto aldehyde carbon of an aldose sugar

A

transketolase

30
Q

what products are produced when transketolase catalyzes transfer of 2-carbon unit from xylulose 5 phosphate to ribose-5-phosphate?

A

7-carbon ketose sedoheptulose-7-phosphate

aldose glyceraldehyde-3-phosphate

31
Q

what happens when the 2 products produced by the transketolase enzyme undergoes TRANSALDOLATION?

A

transaldolase catalyzes transfer of 3-carbon dihydroxyacetone moiety from ketose sedoheptulose-7-phosphate onto aldose glyceraldehyde-3-phosphate to form

KETOSE FRUCTOSE-6-PHOSPHATE and 4-carbon aldose ERYTHROSE-4-PHOSPHATE

32
Q

what co-factors are needed by transketolase?

A

magnesium

thiamin diphosphate (vit B1)

33
Q

how does the reaction catalyzed by transadolase proceed?

A
  • no co-factor

- rxn proceeds via intermediate formation of Schiff base of dihydroxyacetone to E-group of a lysine residue in enzyme

34
Q

xylulose-5-phosphate(donor) will react w/ erythrose-4-phospate (acceptor) by donating GLYCOLALDEHYDE to produce

A

fructose-6-phosphate
GA3P

rxn catalyzed by transketolase

35
Q

differences b/w PPP and glycolysis

A
  • NADP+ vs NAD+
  • production of CO2 vs CO2 not produced
  • No ATP generated vs product ATP
36
Q

how are PPP and glycolysis connected?

A

xylulose-5-phosphate activates protein phosphatase that DEPHOSPHORYLATES 6-PFK-2/F26Bisphatase bifunctional enzyme, activating GLYCOLYSIS.

X5P also activates protein phosphatase that initiates nuclear translocation & DNA binding of carb response element-binding protein, leading to increased FA synthesis.

37
Q

PPP is active in what organs or parts of the body?

A 
liver
adipose tissue
erythrocytes
lactating mammary gland
adrenal cortex
thyroid 
testis
38
Q

PPP activity is low in what parts of the body?

A

skeletal muscle

non-lactating mammary gland

39
Q

can synthesis of G6P dehydrogenase and 6-phosphogluconate dehydrogenase be induced by insulin?

A

yes it can in fed state, when lipogenesis increases

40
Q

why do tissues have to synthesize the ribose they need for nucleotide & nucleic acid synthesis from PPP?

A

b/c little or no ribose circulates in th bloodstream

41
Q

an enzyme that contains selenium analog of cysteine (selenocysteine) at active site

A

glutathione peroxidase

42
Q

alternative oxidative pathway for glucose that also does not yield ATP like PPP

A

uronic acid pathway

43
Q

why are humans unable to synthesize ascorbic acid?

A

due to absence of L-gluconalactone oxidase

44
Q

why does fructose undergo more rapid glycolysis in liver than does glucose?

A

fructose bypasses regulatory step catalyzed by phosphofructokinase

45
Q

why is galactose required in the body?

A
  • formation of lactose in lactation

- constituent of glycolipids (cerebrosides), proteoglycans, & glycoproteins

46
Q

enzyme that doesn’t act on glucose & its activity is not affected by fasting or by insulin

A

fructokinase

47
Q

what enzyme cleaves F1P to D-glyceraldehyde & dihydroxyacetone phosphate?

A

aldolase B

48
Q

how does d-glyceraldehyde enter glycolysis?

A

phosphorylation to GA3P catalyzed by TRIOKINASE

49
Q

enzyme responsible for secretion of sorbitol into fetal blood

A

aldose reductase

50
Q

enzyme responsible for conversion of sorbitol into fructose

A

sorbitol dehydrogenase

51
Q

cataract is more severe if condition is caused by?

A

a defect in uridyl transferase

52
Q

what substance accumulates in the eyes that is formed from galactose?

A

galactitol

53
Q

inability to metabolize galactose occurs in _____? and best known cause for it is ______?

A

galactosemias, uridyl transferase deficiency

Biochemistry (8 decks)

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