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Enzymes Flashcards

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1
Q

Carbamoyl Phosphate Synthetase II

- Pyrimidine Synthesis (rate-limiting)

A

Glutamine + CO2 + 2ATP –> Carbamoyl phosphate

  • Cytosol
  • N from glutamine
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2
Q

UMP Synthase

- Pyrimidine Synthesis

A

Orotic acid + PRPP –> UMP

- Impaired in orotic aciduria

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3
Q

Ribonucleotide Reductase

- Pyrimidine Synthesis

A

UDP –> dUDP

- Inhibited by hydroxyurea (sickle cell, cancer)

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4
Q

Thymidylate Synthase

- Pyrimidine Synthesis

A

dUMP –> dTMP

  • uses THF (have to have folic acid to synthesize DNA)
  • Inhibited by 5-FU (cancer)
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5
Q

Dihydrofolate Reductase

- Pyrimidine Synthesis

A

Regenerates THF from DHF after it’s used by thimidylate synthase
- Inhibited by methotrexate (eukaryotes), trimethoprim (prokaryotes), and pyrimethamine (protozoa)

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6
Q

Glutamine PRPP Amidotransferase

- Purine Synthesis (rate-limiting)

A

PRPP –> IMP

- Inhibited by 6-MP (cancer)

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7
Q

IMP Dehydrogenase

- Purine Synthesis

A

IMP –> GMP

- Inhibited by mycophenolate

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8
Q

Xanthine Oxidase

- Purine Salvage

A

Hypoxanthine –> xanthine
Xanthine –> uric acid
- Inhibited by allopurinol and febuxostate (gout)
- Metabolizes azathioprine and 6-MP (increases toxicity)

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9
Q

HGPRT

- Purine Salvage

A

Hypoxanthine –> IMP
Guanine –> GMP
- Deficient in Lesch Nyhan Syndrome

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10
Q

Adenosine Deaminase

- Purine salvage

A

Adenosine –> Inosine

- Deficiency causes SCID

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11
Q

Glucokinase

  • Glycolysis (first committed step)
  • Glycogen synthesis
A

Glucose –> glucose-6-phosphate

  • Found in liver, beta cells of pancreas
  • High Km (needs a lot of glucose)
  • High Vmax (works quickly)
  • Induced by insulin
  • Mutation –> maturity onset diabetes of the young
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12
Q

Hexokinase

  • Glycolysis (first commited step)
  • Glycogen synthesis
A

Glucose–> glucose-6-phosphate

  • Most tissues
  • Low Km (higher affinity)
  • Low Vmax (low capacity)
  • Not induced by insulin
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13
Q

Phosphofructokinase-1

  • Glycolysis (rate-limiting step)
  • Requires ATP
A

F-6-P –> F-1,6-BP

  • Stimulated by: AMP (not a lot of ATP around), F-2,6-BP
  • Inhibited by: ATP (high energy state), citrate (substrate of TCA cycle)
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14
Q

Pyruvate Kinase

  • Glycolysis
  • Produces ATP
A

Phosphoenolpyruvate –> pyruvate –> TCA cycle
Stimulated by: F-1,6-BP (upstream substrate)
Inhibited by: ATP, alanine (high energy state)

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15
Q

Phosphofructokinase-2

- Glycolysis (regulating step)

A

F-6-P –> F-2,6-BP –> allosteric activator of PFK-1 (glycolysis substrate)
Stimulated by: insulin (fed state)

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16
Q

Fructose-bisphosphatase-2

- Glycolysis (regulating step)

A

F-2,6-BP –> F6P –> gluconeogenesis

Stimulated by: glucagon (fasting)

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17
Q

Pyruvate Carboxylase

  • Gluconeogenesis
  • Requires biotin
A

Pyruvate –> oxaloacetate

  • Requires biotin
  • Stimulated by: acetyl Co-A
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18
Q

PEP Carboxykinase

- Gluconeogenesis

A

Oxaloacetate –> PEP

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19
Q

Fructose-1,6-Bisphosphatase

- Gluconeogenesis (rate-limiting)

A

F-1,6-BP –> F6P

  • Stimulated by: ATP (high energy)
  • Inhibited by: AMP, F-2,6-BP (energy deficient)
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20
Q

Glucose-6-Phosphatase

  • Gluconeogenesis (last step)
  • Glycogenolysis (last step)
A

G6P –> glucose

  • deficient in Von Gierke Disease
  • NOT in muscles (can’t do gluconeogenesis) - only reason muscle cells break down glycogen is for its own use (doesn’t share energy)
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21
Q

Glycogen Synthase

- Glycogen synthesis (rate-limiting)

A

UDP-Glucose –> Glycogen

  • Makes alpha-1,4-glycosidic linkages
  • Stimulated by insulin
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22
Q

Glycogen Phosphorylase

- Glycogenolysis

A

Liberates G1P residues off branched glycogen until 4 glucose units remain on a branch

  • Breaks alpha-1,4 linkage
  • Inhibited by: ATP, G6P, glucose, insulin
  • Stimulated by: glucagon (by activating GP kinase), Epi (Gs)
  • Deficient in McArdle Disease (Type V)
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23
Q

Phosphoglucomutase

- Glycogenolysis

A

G1P –> G6P

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24
Q

Debranching Enzyme

- Glycogenolysis

A

4-alpha-D-glucanotransferase: removes 3 molecules of G1P from branch to linkage
alpha-1,6-glucosidase: cleaves off last residue –> liberates glucose
- Deficient in Cori Diseaes (Type III)

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25
Pyruvate Carboxylase - Pyruvate Metabolism - Requires biotin
Pyruvate + ATP + CO2 --> oxaloacetate --> TCA cycle or gluconeogenesis - Cofactor: biotin
26
Pyruvate Dehydrogenase - Pyruvate Metabolism - Requires B1, B2, B3, B5, lipoic acid
Pyruvate + NAD+ + CoA --> AcetylCoA + CO2 + NADH - Transition from glycolysis to TCA cycle - Cofactors: TPP (B1), lipoic acid (inhibited by arsenic - garlic breath), Coenzyme A (B5), FAD (B2), NAD+ (B3) - Activated by: increased NAD+/NADH ratio, high ADP, high Ca2+
27
Lactic Acid Dehydrogenase - Pyruvate Metabolism - Requires B3
Pyruvate --> lactate (requires NADH) --> Cori Cycle - End of anaerobic glycolysis (major pathway in RBCs, WBCs, kidney medulla, lens, testes, and cornea) - For cells that like mitochondria - Deficiency leads to exercise intolerance
28
Alanine Aminotransferase - Pyruvate Metabolism - Requires B6
Pyruvate --> Alanine --> Cahill Cycle | - Alanine carries amino groups to the liver from muscle
29
Citrate Synthase | - TCA Cycle
Acetyl-CoA (2C) + oxaloacetate (4C) --> Citrate (6C) | - Inhibited by ATP
30
Isocitrate Dehydrogenase | -TCA Cycle
Isocitrate (6C) --> CO2 + NADH + alpha-ketoglutarate (5C) - Inhibited by: ATP, NADH - Stimulated by: ADP
31
Alpha-Ketoglutarate Dehydrogenase - TCA Cycle (highly regulated) - Cofactors: B1, B2, B3, B5, lipoic acid
Alpha-KG (5C) --> CO2 + NADH + succinyl CoA (4C) - Inhibited by: ATP, NADH, succinyl CoA - Requires same cofactors as pyruvate dehydrogenase complex (B1, B2, B3, B5, lipoic acid)
32
Complex 1 | - ETC (oxidative phosphorylation)
- NADH --> NAD+ --> 2.5 ATP | - Inhibited by Amytal (barbiturate), Rotenone (pesticide/fish poison), MPP (also causes Parkinson's)
33
``` Complex II (Succinate Dehydrogenase) - ETC (oxidative phosphorylation) ```
FADH2 --> FAD --> 1.5 ATP
34
Complex III | - ETC (oxidative phosphorylation)
Inhibited by Antimycin A (fish poison)
35
Complex IV | - ETC (oxidative phosphorylation)
1/2 O2 + 2H+ --> H2O | - Inhibited by CN, sodium azide, CO, H2S
36
``` Complex V (ATPase) - ETC (oxidative phosphorylation) ```
- Generates ATP | - Inhibited by Oligomycin (macrolide ABx)
37
Alanine Aminotransferase - Transamination - Cofactor: pyridoxal phosphate (B6)
Alanine + alpha-KG --> pyruvate + glutamate | - Marker for hepatocyte damage
38
Aspartate Transaminase - Transamination - Cofactor: pyridoxal phosphate (B6)
Aspartate + alpha-KG --> oxaloacetate + glutamate | - Marker for hepatocyte damage
39
G6P Dehydrogenase | - HMP Shunt (pentose phosphate pathway) [rate limiting step]
G6P + NADP+ --> 2 NADPH + Ribulose-5-P + CO2 - NADPH --> glutathione reduction inside RBCs, FA and cholesterol biosynthesis - Ribulose-5-P --> PRPP --> nucleotide synthesis (ribose backbones) - Inhibited by NADPH - Deficiency --> hemolytic anemia
40
NADPH Oxidase - Respiratory Burst - Requires NADPH
O2 --> superoxide ion - In phagolysosome - Deficiency: chronic granulomatous disease
41
Superoxide Dismutase | - Respiratory burst
Superoxide ion --> hydrogen peroxide | - In phagolysosome
42
Myeloperoxidase | - Respiratory burst
Hydrogen peroxide + Cl- --> hypochlorous acid (bleach) | - In phagolysosome
43
Glutathione Peroxidase | - RBC Detox
H2O2 + reduced glutathione (important antioxidant) --> H2O + glutathione disulfide (oxidized)
44
Glutathione Reductase | - Uses NADPH (from G6PD)
NADPH + glutathione disulfide (oxidized) --> NADP+ + reduced glutathione
45
Fructokinase - Fructose metabolism - Requires ATP
Fructose + ATP --> F1P | - Defect: essential fructosuria (benign)
46
Aldolase B | - Fructose metabolism
F1P --> dihydroxyacetone P and glyceraldehyde | - Defect: fructose intolerance (inhibits glycogenolysis and gluconeogenesis --> fasting hypoglycemia)
47
Galactokinase - Galactose metabolism - Requires ATP
Galactose + ATP --> Galactose-1-P | - Defect: galactokinase deficiency (infantile cataracts)
48
Aldose Reductase | - Galactose metabolism
Galactose --> galactitol | - too much galactitol --> cataracts
49
Galactose-1-Phosphate Uridyltransferase | - Galactose metabolism
Galactose-1-P + UDP-Glucose --> Glucose-1-P + UDP-Galactose --> glycolysis/glycogenolysis - Defect: classic galactosemia
50
HMG-CoA Synthase | - Ketogenesis (rate-limiting)
Makes ketone bodies during starvation
51
Alcohol Dehydrogenase - Ethanol metabolism - NAD+ is limiting reagent
Ethanol + NAD+ --> Acetaldehyde + NADH - 0-order kinetics - Acetaldehyde is what causes hangover - Inhibited by Fomepizole (used for methanol or ethylene glycol poisoning)
52
Acetaldehyde Dehydrogenase - Ethanol metabolism - NAD+ is limiting reagent
Acetaldehyde + NAD+ --> Acetate + NADH | - Inhibited by disulfiram (acetaldehyde accumulates --> hangover sx)
53
ApoE | - Lipid transport
Mediates remnant uptake
54
Apo A-1 | - Lipid transport
Activates LCAT --> catalyzes esterification of cholesterol | - Nascent HDL --> mature HDL
55
Apo C-II | - Lipid transport
Lipoprotein lipase cofactor | - Deficient in Type I (Hyperchylomicronemia)
56
Apo B-48 | - Lipid transport
Mediates chylomicron secretion
57
Apo B-100 | - Lipid transport
Mediates VLDL secretion - Binds LDL R - Defective binding in Type IIa (familial hypercholesterolemia)
58
HMG-CoA Reductase | - Cholesterol synthesis (rate limiting step)
Converts HMG-CoA to mevalonate - Induced by insulin - Inhibited by statins - Cholesterol synthesis starts with acetyl CoA
59
Acetyl CoA Carboxylase | - FA Synthesis (rate limiting step)
- Cytoplasm of hepatocytes
60
Carnitine Acyltransferase 1 (Caritine Palmitoyltransferase 1) - FA Degradation (rate limiting step)
- Mitochondrial matrix
61
Phenylalanine Hydroxylase - Catecholamine synthesis/tyrosine catabolism - Cofactor: BH4
Phenylalanine --> Tyrosine - Tyrosine used to make thyroxine - Deficient: PKU
62
Tyrosine Hydroxylase - Catecholamine synthesis/ tyrosine catabolism - Cofactor: BH4
Tyrosine --> Dopa | - Dopa used to make melanin
63
Dopa Decarboxylase - Catecholamine synthesis/tyrosine catabolism - Cofactor: B6
DOPA --> Dopamine | - Inhibited by Carbidopa (rx for Parkinson's)
64
Dopa-beta-hydroxylase - Catecholamine synthesis/tyrosine catabolism - Cofactor: Vit C
Dopamine --> NE | Deficiency: nasal congestion, ptosis, orthostatic hypotension
65
Phenylethanolamine-N-methyltransferase - Catecholamine synthesis/tyrosine catabolism - Cofactor: SAM (transfers methyl groups)
NE --> Epi | - Stimulated by cortisol
66
Carbamoyl Phosphate Synthetase I - Urea cycle (rate-limiting step) - Requires ATP
CO2 + NH3 --> Carbamoyl phosphate | - In mitochondria
67
Ornithine Transcarbamylase | - Urea cycle
Carbamoyl phosphate + ornithine --> citrulline
68
Tyrosinase | - Catecholamine synthesis/tyrosine catabolism
Dopa --> melanin | - Deficiency: albinism
69
Homogentisate Oxidase | - Catecholamine synthesis/tyrosine catabolism
``` Homogentisic acid (from Tyr) --> maleylacetoacetic acid --> fumarate --> TCA cycle - Deficiency: alkaptonuria (ochronosis, black urine) ```
70
Cystathione Synthase - Homocysteine metabolism - Cofactor: B6
Serine + homocysteine --> cystathione | Deficiency: homocystinuria
71
Methionine Synthase - Homocysteine metabolism - Cofactor: B12
Homosysteine --> methionine | Deficiency: homocystinuria
72
Alpha-ketoacid Dehydrogenase - AA metabolism - Cofactors: thiamine pyrophosphate, lipoate, coenzyme A, FAD, NAD
Degrades branched AA (isoleucine, leucine, valine) | Deficiency: maple syrup urine disease

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