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Medical Biochemistry > Ch. 14: CHO Metabolism II: Gluconeogenesis, Glycogen > Flashcards

Ch. 14: CHO Metabolism II: Gluconeogenesis, Glycogen Flashcards

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USMLE® Step 1 flashcards
1
Q

What are the substrates for gluconeogenesis?

A 
Lactate
Pyruvate
Glycerol (fr TG in adipose)
Glucogenic a.a.
(Propionate: ruminants)
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2
Q

Where does gluconeogensis occur? During starvation/metabolic acidosis?

A

85-95% in liver

Kidneys contribute up to 50%
Enterocytes not more than 5%

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3
Q

How much energy needed for 2 pyruvate ➡️ 1 glucose?

A

4 ATP
2 GTP
2 NADH

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4
Q

Fxns of gluconeogenesis?

A

1) Maintain [glucose]
2) Use lactate (glycolysis) & glycerol (fat breakdown)
3) Acid-base balance
4) a.a. balance
5) provision of biosynthetic precursors

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5
Q

Main 4 enzymes of gluconeogenesis? (Differ from glycolysis)

A

1) Pyruvate carboxylase
2) PEP carboxykinase
3) Fructose-1,6-bisphosphatase
4) Glucose-6-phosphatase

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6
Q

What is pyruvate carboxylase attached to? How attached?

A

Attached to biotin via lysine ➖charge

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7
Q

3 ways oxaloacetate can get out of mitochondria?

A

1) ➡️ PEP (PEP carboxykinase in MT and cytosol)
2) ➡️ Asp
3) ➡️ Malate

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8
Q

Of 2 shuttles which move oxaloacetate from MT ➡️ cytosol, which is major? Why?

A

Malate shuttle = major

Asp shuttle = minor (also need alpha-ketoglutarate in TCA cycle)

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9
Q

Mechanism of activation & transfer of CO2 to pyruvate?

A

1) from HCO3- TO biotin attached to pyruvate carboxylase
2) TO pyruvate ➡️ oxaloacetate
3) oxaloacetate reduced ➡️ malate
4) malate moves into cytosol, oxidized to oxaloacetate
5) decarboxylated to PEP

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10
Q

How is fructose 1,6 bisphosphatase regulated?

A

➖: AMP, fructose 2,6-bisphosphate (signaling via glucagon or epinephrine)

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11
Q

Dephosphorylation of G6P occurs where? Does not occur where?

A

Liver (& kidneys?)

NOT muscle!

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12
Q

4 ways gluconeogenesis is regulated?

A

1) glucagon
2) substrate availability
3) allosteric ➕ by acetyl CoA
4) allosteric ➖ by AMP

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13
Q

What are the glucogenic a.a.?

A

All except Lys & Leu (KL)

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14
Q

What a.a. are both glucogenic & ketogenic?

A

Trp, Ile, Phe, Thr, Tyr

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15
Q

Which a.a. is most important a.a. substrate for gluconeogenesis?

A

Alanine

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16
Q

Most tissues produce lactate ➡️ removed by liver & kidneys

How?

A

Actively convert lactate ➡️ glucose

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17
Q

How is severe hypoglycemia defined? (Measure)

A

Glucose levels ⬇️ 40 mg/dL (adults) or ⬇️ 30 mg/dL (neonates)

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18
Q

What is multiple carboxylase deficiency?

A

Genetic defect in holocarboxylase synthetase (➡️ no biotin attachment)

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19
Q

Which carboxylase need biotin to function?

A

Pyruvate
Acetyl CoA
Propionyl CoA
Beta-methylcrotonyl CoA

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20
Q

Effects of multiple carboxylase deficiency?

A

Develop. retardation
Ketoacidosis
Hair loss
Erythematous rash

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21
Q

What is Von Gierke’s disease?

A

Genetic defect in G6Pase ➡️ G6P trapped in cell (liver)

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22
Q

Effects of Von Gierke’s disease?

A 
Enlarged liver
Hypoglycemia
Lactic acidosis
Hyperlipidemia
Hyperuricemia (purine ➡️ uric acid)
23
Q

What is hypoglycin A?

A

Toxin of unripe akee fruit

24
Q

How does Hypoglycin A causes hypoglycemia? (Mechanism)

A

Forms non-metabolizable esters with CoA & carnitine ➡️ ⬇️ CoA & carnitine pools ➡️ FA oxidation inhibited ➡️ gluconeogenesis inhibited (Long chain FA oxidation main source of ATP for gluconeogenesis)

25
Q

Where is glycogen stored? Fxn of glycogen at each site?

A

Muscle: greater total amt
glycogen ➡️ G6P ➡️ energy

Liver: greater concentration
Glycogen ➡️ G6P ➡️ glucose ➡️ blood glucose

26
Q

What two bonds are formed in glycogen?

A

Alpha 1➡️4 glycosidic bonds

Alpha 1➡️6 glycosidic bonds (branching)

27
Q

Glycogen synthesis pathway?

A

G6P ➡️ G1P ➡️ UDP-glucose ➡️ glycogen

28
Q

Glycogenolysis pathway?

A

Glycogen ➡️ G1P ➡️ G6P

29
Q

Enzymes in glycogen synthesis?

A

1) Phosphoglucomutase (G6P ➡️ G1P)
2) UDP glucose pyrophosphorylase (G1P ➡️ UDP glucose)
3) Glycogen Synthase, branching enzyme & 4,6 transferase (UDP glucose ➡️ glycogen)

30
Q

What does UDP-glucose attach to?

A

Glycogenin (via OH of tyr residue)

31
Q

Autocatalysis (adding glucosyl units to glycogen via UDP glucose) occurs up to how many sugar residues?

A

7 residues ➡️ then glycogen synthase used

32
Q

Enzymes in glycogenolysis?

A

Glycogen phosphorylase & debranching enzyme (Glycogen ➡️ G1P)

Phosphoglucomutase (G1P ➡️ G1,6P ➡️ G6P)

33
Q

Glycogen-related diseases:

Type II: Pompe disease?

A

Lysosomal alpha 1➡️4 & 1➡️6 glucosidase deficiency

34
Q

Pompe disease: main characteristics?

A

⬆️ [glycogen] in lysosomes

Massive cardiomegaly, heart failure

35
Q

Glycogen-related diseases:

Type III: Cori/Forbes’ disease (limit dextrinosis)?

A

4:4 transferase deficiency
1:6 glucosidase deficiency
(Absence of debranching enzyme)

36
Q

Cori/Forbes’ disease: main characteristics?

A

Fasting hypoglycemia

Abnormal glycogen structure

37
Q

Glycogen-related diseases:

Type IV: Andersen’s disease (amylopectinosis)?

A

Absence of debranching enzyme

38
Q

Andersen’s disease: main characteristics?

A 
Abnormal glycogen (few branch pts)
Death via cardiac/liver failure (1st year of life)
39
Q

Glycogen-related diseases:

Type V: McArdle syndrome?

A

Skeletal muscle glycogen phosphorylase deficiency

Myophosphorylase deficiency

40
Q

McArdle syndrome: main characteristics?

A

Muscle cramping after exercise
⬆️ glycogen content in muscles
Little/no lactate after exercise

41
Q

Glycogen-related diseases:

Type VI: Hers’ disease?

A

Liver phosphorylase deficiency

42
Q

Hers’ disease: main characteristics?

A

⬆️ glycogen in liver

Hypoglycemia

43
Q

Glycogen-related diseases:

Type VII: Tarui’s disease?

A

PFK deficiency in muscle & erythrocytes

44
Q

Tarui’s disease: main characteristics?

A

Muscle cramping after exercise
⬆️ glycogen content in muscles
Little/no lactate after exercise
Hemolytic anemia

45
Q

What regulates glycogen metabolism in muscle?

A

Epinephrine: ➕ lysis, ➖ synthesis

Insulin: ➖ lysis, ➕ synthesis

Ca2+: ➕ lysis

46
Q

What regulates glycogen metabolism in the liver?

A

Glucagon: ➕ adenylyl cyclase & lysis, ➖ synthesis

Insulin: ➕ synthesis

Governing force = glucagon:insulin ratio

47
Q

MoA of glycogen breakdown in muscle?

A

Epi ➡️ ➕AC, ⬆️ cAMP ➡️ ➕ protein kinase A ➡️ ➕ phosphorylase kinase A ➡️ ➕ phosphorylase A (glycogen phosphorylase) ➡️ glycogen breakdown

Ca2+ also ➕phosphorylase kinase A (binds to it’s calmodulin)

48
Q

MoA of inhibiting glycogen synthesis during glycogen breakdown?

A

Epi ➡️ ➕AC, ⬆️ cAMP ➡️ ➕ protein kinase A ➡️ ➖ glycogen synthase ➡️ inactivates glycogen synthesis

49
Q

MoA of glycogen synthesis in muscle?

A

Insulin ➡️ ➕ protein phosphatase ➡️ ➕ glycogen synthase ➡️ glycogen synthesis

Glycogen synthase also ➕ by Glucose-6-P

50
Q

Inhibitors of glycogen phosphorylase in liver? In muscle?

A

Liver: G6P, ATP, glucose

Muscle: G6P, ATP

51
Q

Activators of glycogen phosphorylase in muscle?

A

AMP: Anoxia & ⬇️ ATP ➡️ AMP activates glycogen phosphorylase A (w/out phosphorylation)

Ca2+

52
Q

Activator of glycogen synthase in muscle & liver?

A

G6P

53
Q

Role of inhibitor-1 in regulating glycogen metabolism in muscle?

A

Epi ➡️ ➕AC, ⬆️ cAMP ➡️ ➕ protein kinase A ➡️ ➕ inhibitor-1P ➡️ ➖ protein phosphatase-1 ➡️ causes:

1) ⬇️ ➖ of phosphorylase kinase A & phosphorylase A
2) ⬇️ ➕ of glycogen synthase B

Medical Biochemistry (23 decks)

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