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Biochemistry > Semester 2: Metabolism of carbohydrates > Flashcards

Semester 2: Metabolism of carbohydrates Flashcards

1
Q

Regulated steps in glycolysis

A

1) Glucose -> glucose-6-p (hexokinase/glucokinase)
2) Fructose-6-p -> F-1,6-bisphosphate (PFK)
3) Phosphoenolpyruvate -> pyruvate (Pyruvate kinase)

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2
Q

Allosteric inhibitor of hexokinase

A

Its product glucose-6-p

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3
Q

What is the enzyme enolase inhibited by and what is it dependent on?

A

Inhibitor: Flouride
Needs: Mg2+, Mn2+

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4
Q

Where does glycolysis take place?

A

Cytosol

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5
Q

What is the end result of glycolysis?

A

Net 2ATP, 2NADH formed + 2 pyruvate

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6
Q

Pyruvate fermentation in yeast: pyruvate decarboxylase

A

Pyruvate to acetaldehyde

  • needs TPP and Mg2+
  • releases CO2
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7
Q

Where can we find PDC?

A

Associated with inner mitochondrial membrane

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8
Q

What are the subunits of PDC?

A

E1: Pyruvate dehydrogenase
E2: Dehydrolipoyl transacetylase
E3: Dehydrolipoyl dehydrogenase

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9
Q

What are the allosteric regulators of E2, E3?

A

Inducers: CoA-SH, NAD+
Inhibitors: Acetyl-CoA + NADH+H

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10
Q

How is E1 activated?

A

Dephosphorylation by PDC phosphatase (Inducers: Ca2+, Insulin)

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11
Q

How is E1 inactivated?

A

Phosphorylation by PDC kinase
(Inducers: Acetyl-CoA, NADH
Inhibitors: Pyruvate, NAD, ADP, AMP)

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12
Q

Where does citric acid cycle take place?

A

Matrix of mitochondria

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13
Q

Irreversible steps in citric acid cycle?

A

1) Acetyl-CoA + oxaloacetate -> citrate (citrate synthase)
2) Isocitrate -> alpha-ketoglutarate (isocitrate DEH)
3) alpha-ketoglutarate -> succinyl-CoA (alpha-ketoglutarate DEH complex)

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14
Q

Inhibitor of the enzyme aconitase?

A

Fluroacetate

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15
Q

Which cofactors are needed for alpha-ketoglutarate DEH complex?

A

Same as in PDC:

  • Thiamin diphosphate
  • Lipoate
  • NAD+
  • FAD
  • CoA
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16
Q

Inhibitor of alpha-ketoglutarate DEH complex?

A

Arsenite

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17
Q

What is the result of citric acid cycle?

A
  • 3NADH formed
  • 1FADH2 formed
  • 1ATP formed
    = 10 ATP formed per turn
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18
Q

Reaction catalyzed by phosphoglucose mutase and the inhibitor of this enzyme

A

glucose-6-p -> glucose-1-p (glycogenesis)

Inhibitor: DIPF

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19
Q

Reaction catalyzed by UDPglc pyrophospphorylase

A

glu-1-p + UTP -> UDP-glucose + PPi

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20
Q

What is the function of glycogenin?

A

Catalyzes transfer of 7 glucose residues from UDPglc in 1->4 link to form glycogen primer (initial step of glycogenesis)

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21
Q

What is the function of glycogen synthase?

A

Formation of glycosidic bond between C-1 on glucose of UDPglc and C-4 of terminal glucose of glycogen

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22
Q

What is the function of branching enzyme?

A

Other name: glycosyl-4,6-transferase

Establishing branch point when glucose is at least 11 glucose residues long (forms 1->6 linkage)

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23
Q

What is the function of glycogen phosphorylase?

A

(Rate limiting step in glycogenolysis)
Cleavage of 1->4 linkages of glycogen to yield glucose-1-p
- Needs PLP

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24
Q

What is the function of debranching enzyme?

A

Two catalytic sites:

1) Glucan transferase: Exposing 1->6 branch point
2) 1,6-glycosidase: Hydrolysis of 1->6 bond to liberate free glucose

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25
Q

How will E, NE, and glucagon regulate glycogenolysis/glycogenesis?

A

Will increase phosphorylation which:

1) Increases activity of glycogen phosphorylase
2) Decreases activity of glycogen synthase

26
Q

Activated/inactivated forms of glycogen phosphorylase?

A

Active: Phosphorylase A
Inactive: Phosphorylase B

27
Q

What is the function of protein-phosphatase 1?

A

Dephosphorylates and inhibits both phosphorylase A and phosphorylase kinase (responsible for the activation of phosphorylase A)

28
Q

What is Von Gierke disease?

  • Characteristics
  • Subtypes
A
  • Glucose-6-phosphatase or transport system is defective
  • Increased glycogen in liver and kidney
  • Hypoglycemia, ketosis, hyperuricemia, hyperlipemia
  • 1/a: Enzyme mutation
  • 1/b: G-6-p transporter mutation
29
Q

What is glycogenosis?

A

Glycogen storage disease (targets liver and muscle)

30
Q

What is McArdle disease?

A
  • Defective phosphorylase in muscle
  • Limited ability to perform strenous exercise because of painful cramps.
  • Second wind: Better tolerance after about 10min
31
Q

What is gluconeogenesis?

A

The process of synthesizing glucose or glycogen from noncarbohydrate precursors

32
Q

What 3 reaction differs from glycolysis in gluconeogenesis?

A

1)
- Pyruvate -> oxaloacetate (pyruvate decarbpxylase)
- Oxaloactetate -> phosphoenolpyruvate (phosphoenolpyruvate carboxykinase)
2) F-1,6,bisphosphate -> fructose-6-p (f-1,6-bisphosphatase)
3) Glucose-6-p -> glucose (g-6-phosphatase)

33
Q

What is cori cycle/lactic acid cycle?

A

Lactate formed by glycolysis in skeletal muscle and erythrocytes is transported to liver and kidney to reform glucose

34
Q

What is MODY?

A

Maturity Onset Diabetes of the Young

- MODY2: 50% mutation in glucokinase gene in pancreatic beta-cells

35
Q

How are the izoenzymes of pyruvate kinase regulated?

A

PK-L (liver): both allosterically and hormonally

PK-M (muscle): not regulated

36
Q

How is glucose and galactose taken up by intestinal cells?

A

Apical mem: By SGLT (sodium-glucose transporter)

Basolat. mem.: GLUT2

37
Q

How is fructose taken up by intestinal cells?

A

Apical mem. : By GLUT5

Basolat. mem. : By GLUT2 + 5

38
Q

In what reactions are Aldolase A/B used?

A
  • Aldolase A: Glycolysis (f-1,6-bisphosphate -> glyceraldehyde-3-p + dihydroxyacetone-p
  • Aldolase B: Alternative pathway (f-1-p -> glyceraldehyde + dihydroxyacetone-p)
39
Q

What is essential fructosuria?

A
  • Fructokinase missing from liver and intestine

- Patient will urinate glucose

40
Q

Fructose intolerance

A

Aldolase B is defective. Lethal!

41
Q

Which reaction is catalyzed by UDP-galactose-1p-uridyltransferase?

A

galactose-1-p -> UDP-galactose

42
Q

Which reaction is catalyzed by 4-epimerase?

A

UDP-galactose -> UDP-glucose

43
Q

Which reaction is catalyzed by UDP-glucose-1p-uridyltransferase?

A

UDP-glucose -> glucose-1-p

44
Q

Galactosemia

A
  • Defect of galactose metabolism
  • Types w/defective enzymes:
    1) galactose-1-p uridyltransferase
    2) galactokinase
    3) UDP-galactose-4-epimerase
45
Q

Lactose synthesis

A
  • 1 glucose molecule needs to be converted to UDP-galactose (several steps)
  • 2nd glucose goes with UDP-galactose to from lactate (via lactose synthase)
46
Q

What is pentose phosphate pathway used for?

A

An alternative route for the metabolism of glucose which does not lead to the formation of ATP

47
Q

Where are the enzymes of PPP located?

A

In cytosol

48
Q

PPP: Irreversible oxidative phase yields?

A

Glucose-6-p undergoes dehydrogenation and decarboxylation to yield ribulose-5-p

49
Q

PPP: Reversible nonoxidative phase yields?

A

Ribulose-5-p converted back to g-6-p by a series of reactions involving mainly two enzymes: transketolase (needs Mg2+ and TPP), transaldolase

50
Q

GLUT1 and GLUT3

A
  • High affinity for glucose (Km low)
  • All cells, except for pancreatic beta-cells and hepatocytes
  • Glucose dependent
51
Q

GLUT2

A
  • Low affinity for glucose (Hight Km)

- In pancreatic beta-cells and hepatocytes

52
Q

GLUT4

A
  • Intermediate affinity
  • Insulin-dependent in skeletal muscle and adipocytes
  • Adjusts glucose consumption to availability
53
Q

GLUT5

A
  • In intestinal epithelial cells and kidney tubular epithelial cells
  • Participates in glucose absorption and re-absorption
54
Q

Inhibitor of succinate dehydrogenase

A

Malonate

55
Q

Substrate level phosphorylation in TCA cycle

A

Succinyl-CoA to succinate via succinyl-CoA synthetase produces GTP

56
Q

Citric acid cycle activated by

A
  • Low NADH/NAD
  • Low ATP/ADP,
  • Low Succinyl-CoA/CoA
  • Ca2+
57
Q

Organs that needs glucose

A

Brain, CNS, kidney medulla, testes, RBC, embryonic tissues

58
Q

How is glucokinase activated?

A
  • When regulator protein is bound to F-1P

- Inactivated when glucokinase is bound to regulator protein and F-6P

59
Q

Allosteric regulators of PFK-1

A

Activators: AMP, F-2,6-P
Inhibitors: ATP, citrate, fatty acids

60
Q

Pyruvate carboxylase

A

Bicarbonate + Pyruvate –> oxaloacetate

- uses ATP and Biotin

Biochemistry (9 decks)

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