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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
How will E, NE, and glucagon regulate glycogenolysis/glycogenesis?
Will increase phosphorylation which: 1) Increases activity of glycogen phosphorylase 2) Decreases activity of glycogen synthase
26
Activated/inactivated forms of glycogen phosphorylase?
Active: Phosphorylase A Inactive: Phosphorylase B
27
What is the function of protein-phosphatase 1?
Dephosphorylates and inhibits both phosphorylase A and phosphorylase kinase (responsible for the activation of phosphorylase A)
28
What is Von Gierke disease? - Characteristics - Subtypes
- 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
What is glycogenosis?
Glycogen storage disease (targets liver and muscle)
30
What is McArdle disease?
- Defective phosphorylase in muscle - Limited ability to perform strenous exercise because of painful cramps. - Second wind: Better tolerance after about 10min
31
What is gluconeogenesis?
The process of synthesizing glucose or glycogen from noncarbohydrate precursors
32
What 3 reaction differs from glycolysis in gluconeogenesis?
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
What is cori cycle/lactic acid cycle?
Lactate formed by glycolysis in skeletal muscle and erythrocytes is transported to liver and kidney to reform glucose
34
What is MODY?
Maturity Onset Diabetes of the Young | - MODY2: 50% mutation in glucokinase gene in pancreatic beta-cells
35
How are the izoenzymes of pyruvate kinase regulated?
PK-L (liver): both allosterically and hormonally | PK-M (muscle): not regulated
36
How is glucose and galactose taken up by intestinal cells?
Apical mem: By SGLT (sodium-glucose transporter) | Basolat. mem.: GLUT2
37
How is fructose taken up by intestinal cells?
Apical mem. : By GLUT5 | Basolat. mem. : By GLUT2 + 5
38
In what reactions are Aldolase A/B used?
- Aldolase A: Glycolysis (f-1,6-bisphosphate -> glyceraldehyde-3-p + dihydroxyacetone-p - Aldolase B: Alternative pathway (f-1-p -> glyceraldehyde + dihydroxyacetone-p)
39
What is essential fructosuria?
- Fructokinase missing from liver and intestine | - Patient will urinate glucose
40
Fructose intolerance
Aldolase B is defective. Lethal!
41
Which reaction is catalyzed by UDP-galactose-1p-uridyltransferase?
galactose-1-p -> UDP-galactose
42
Which reaction is catalyzed by 4-epimerase?
UDP-galactose -> UDP-glucose
43
Which reaction is catalyzed by UDP-glucose-1p-uridyltransferase?
UDP-glucose -> glucose-1-p
44
Galactosemia
- Defect of galactose metabolism - Types w/defective enzymes: 1) galactose-1-p uridyltransferase 2) galactokinase 3) UDP-galactose-4-epimerase
45
Lactose synthesis
- 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
What is pentose phosphate pathway used for?
An alternative route for the metabolism of glucose which does not lead to the formation of ATP
47
Where are the enzymes of PPP located?
In cytosol
48
PPP: Irreversible oxidative phase yields?
Glucose-6-p undergoes dehydrogenation and decarboxylation to yield ribulose-5-p
49
PPP: Reversible nonoxidative phase yields?
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
GLUT1 and GLUT3
- High affinity for glucose (Km low) - All cells, except for pancreatic beta-cells and hepatocytes - Glucose dependent
51
GLUT2
- Low affinity for glucose (Hight Km) | - In pancreatic beta-cells and hepatocytes
52
GLUT4
- Intermediate affinity - Insulin-dependent in skeletal muscle and adipocytes - Adjusts glucose consumption to availability
53
GLUT5
- In intestinal epithelial cells and kidney tubular epithelial cells - Participates in glucose absorption and re-absorption
54
Inhibitor of succinate dehydrogenase
Malonate
55
Substrate level phosphorylation in TCA cycle
Succinyl-CoA to succinate via succinyl-CoA synthetase produces GTP
56
Citric acid cycle activated by
- Low NADH/NAD - Low ATP/ADP, - Low Succinyl-CoA/CoA - Ca2+
57
Organs that needs glucose
Brain, CNS, kidney medulla, testes, RBC, embryonic tissues
58
How is glucokinase activated?
- When regulator protein is bound to F-1P | - Inactivated when glucokinase is bound to regulator protein and F-6P
59
Allosteric regulators of PFK-1
Activators: AMP, F-2,6-P Inhibitors: ATP, citrate, fatty acids
60
Pyruvate carboxylase
Bicarbonate + Pyruvate --> oxaloacetate | - uses ATP and Biotin

Biochemistry (9 decks)

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