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Biochem NBME > Metabolism > Flashcards

Metabolism Flashcards

1
Q

Ethanol metabolism

A

FOMEpizole—inhibits alcohol dehydrogenase and is an antidote For Overdoses of Methanol or Ethylene glycol.

Disulfiram—inhibits acetaldehyde dehydrogenase (acetaldehyde accumulates, contributing to hangover symptoms), discouraging drinking.

NAD+ is the limiting reagent.

Alcohol dehydrogenase operates via zero-order kinetics.

Ethanol metabolism increase NADH/NAD+ ratio in liver, causing: ƒ
Pyruvate -> lactate (lactic acidosis) ƒ
Oxaloacetate -> malate (prevents gluconeogenesis -> fasting hypoglycemia)
Dihydroxyacetone phosphate -> glycerol3-phosphate (combines with fatty acids to make triglycerides -> hepatosteatosis)

End result is clinical picture seen in chronic alcoholism.

Additionally, increased NADH/NAD+ ratio disfavors TCA production of NADH ->increased utilization of acetyl-CoA for ketogenesis (for ketoacidosis) and lipogenesis (for hepatosteatosis)

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2
Q

Mitochondria

A

Fatty acid oxidation (β-oxidation), acetylCoA production, TCA cycle, oxidative phosphorylation, ketogenesis

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3
Q

Cytoplasm

A

Glycolysis, HMP shunt, and synthesis of steroids (SER), proteins (ribosomes, RER), fatty acids, cholesterol, and nucleotides

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4
Q

Mitochondria & Cytoplasm

A

Heme synthesis, Urea cycle, Gluconeogenesis

HUGs take two (ie, both

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5
Q

Kinase

A

Catalyzes transfer of a phosphate group from a high-energy molecule (usually ATP) to a substrate (eg, phosphofructokinase).

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6
Q

Phosphorylase

A

Adds inorganic phosphate onto substrate without using ATP (eg, glycogen phosphorylase)

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7
Q

Phosphatase

A

Removes phosphate group from substrate (eg, fructose-1,6-bisphosphatase)

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8
Q

Dehydrogenase

A

Catalyzes oxidation-reduction reactions (eg, pyruvate dehydrogenase)

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9
Q

Hydroxylase

A

Adds hydroxyl group (−OH) onto substrate (eg, tyrosine hydroxylase)

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10
Q

Carboxylase

A

Transfers CO2 groups with the help of biotin (eg, pyruvate carboxylase)

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11
Q

Mutase

A

Relocates a functional group within a molecule (eg, vitamin B12–dependent methylmalonyl-CoA mutase).

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12
Q

Synthase/synthetase

A

Combines 2 molecules into 1 (condensation reaction) either using an energy source (synthase, eg, glycogen synthase) or not (synthetase, eg, PRPP synthetase)

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13
Q

Glycolysis

A

CONTROL ENZYME:
Phosphofructokinase-1 (PFK-1)

REGULATORS:
AMP ⊕, fructose-2,6-bisphosphate ⊕
ATP ⊝, citrate⊝

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14
Q

Gluconeogenesis

A

CONTROL ENZYME:
Fructose-1,6-bisphosphatase

REGULATORS:
Citrate ⊕
AMP ⊝, fructose-2,6-bisphosphate ⊝

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15
Q

TCA cycle

A

CONTROL ENZYME:
Isocitrate dehydrogenase

REGULATORS:
ADP ⊕
ATP ⊝, NADH ⊝

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16
Q

Glycogenesis

A

CONTROL ENZYME:
Glycogen synthase

REGULATORS:
Glucose-6-phosphate ⊕, insulin ⊕, cortisol ⊕
Epinephrine ⊝, glucagon⊝

17
Q

Glycogenolysis

A

CONTROL ENZYME:
Glycogen phosphorylase

REGULATORS:
Epinephrine ⊕, glucagon ⊕, AMP ⊕
Glucose-6-phosphate ⊝, insulin⊝, ATP ⊝

18
Q

HMP shunt

A

CONTROL ENZYME:
Glucose-6-phosphate dehydrogenase (G6PD)

REGULATORS:
NADP+ ⊕
NADPH ⊝

19
Q

De novo pyrimidine synthesis

A

CONTROL ENZYME:
Carbamoyl phosphate synthetase II

REGULATORS:
ATP ⊕, PRPP ⊕
UTP ⊝

20
Q

De novo purine synthesis

A

CONTROL ENZYME:
Glutamine-phosphoribosylpyrophosphate (PRPP) amidotransferase

REGULATORS:
AMP ⊝, inosine monophosphate (IMP) ⊝, GMP ⊝

21
Q

Urea cycle

A

CONTROL ENZYME:
Carbamoyl phosphate synthetase I

REGULATORS:
N-acetylglutamate ⊕

22
Q

Fatty acid synthesis

A

CONTROL ENZYME:
Acetyl-CoA carboxylase (ACC)

REGULATORS:
Insulin ⊕, citrate ⊕
Glucagon ⊝, palmitoyl-CoA ⊝

23
Q

Fatty acid oxidation

A

CONTROL ENZYME:
Carnitine acyltransferase I

REGULATORS:
Malonyl-CoA ⊝

24
Q

Ketogenesis

A

CONTROL ENZYME:

HMG-CoA synthase

25
Q

Cholesterol synthesis

A

CONTROL ENZYME:
HMG-CoA reductase

REGULATORS:
Insulin ⊕, thyroxine ⊕
Glucagon ⊝, cholesterol⊝

26
Q

ATP production

A

Aerobic metabolism of glucose produces 32 net ATP via malate-aspartate shuttle (heart and liver), 30 net ATP via glycerol-3-phosphate shuttle (muscle).

Anaerobic glycolysis produces only 2 net ATP per glucose molecule.

ATP hydrolysis can be coupled to energetically unfavorable reactions.

Arsenic causes glycolysis to produce zero net ATP.

27
Q

Activated carriers

A

ATP -> Phosphoryl groups

NADH, NADPH, FADH2 -> Electrons

CoA, lipoamide -> Acyl groups

Biotin -> CO2

Tetrahydrofolates -> 1-carbon units

S-adenosylmethionine (SAM) -> CH3 groups

TPP -> Aldehydes

28
Q

Universal electron acceptors

A

Nicotinamides (NAD+ from vitamin B3, NADP+) and flavin nucleotides (FAD+ from vitamin B2).

NAD+ is generally used in catabolic processes to carry reducing equivalents away as NADH.

NADPH is used in anabolic processes (steroid and fatty acid synthesis) as a supply of reducing equivalents.

NADPH is a product of the HMP shunt.

NADPH is used in: ƒ
Anabolic processes
Respiratory burst
Cytochrome P-450 system
Glutathione reductase
29
Q

Hexokinase vs glucokinase

A

HEXOKINASE

  • Most tissues, except liver and pancreatic β cells
  • low Km (high affinity)
  • low Vmax (low capacity)
  • not induced by insulin
  • feedback inhibited by G6P

GLUCOKINASE

  • Liver, β cells of pancreas
  • high Km (low affinity)
  • high Vmax (high capacity)
  • induced by insulin
  • feedback not inhibited by G6P

Biochem NBME (6 decks)

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