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USMLE GAME TIME > Biochemistry - Part 2 - More important concepts > Flashcards

Biochemistry - Part 2 - More important concepts Flashcards

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USMLE® Step 1 flashcards
1
Q

What enzyme defect causes PKU?

A

Either defect in phenylalanine hydroxylase (more common) or defect in dihydrobiopterin reductase (regenerates BH4 from BH2).

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2
Q

What is the musty / mousy odor in PKU due to?

A

Accumulation of abnormal phenylalanine metabolites

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3
Q

Severe intellectual disability, seizures, respiratory failure in a young boy with substantia nigra, locus ceruleus, vagal nucleus dorsalis pallor

A

PKU

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4
Q

Phenyllactate

A

A phenylalanine metabolite, along with phenylacetate, which accumulates in PKU and contributes to the brain damage

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5
Q

Path from tyrosine to the TCA cycle

A

Tyrosine –>homogentisate -(homogentisic acid oxidase)-> maleylacetoacetate -> fumarylacetoacetate -> fumarate -> TCA

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6
Q

What are the branched chain amino acids?

A

I Love Vermont Maple syrup - Isoleucine, leucine, Valine

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7
Q

What enzyme catalyzes decarboxylation of the alpha-ketoacid derivatives of the branched chain amino acids?

A

Branched chain ketoacid dehydrogenase

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8
Q

Ptosis, orthostatic hypotension, hypoglycemia, hypothermia

A

Defect in dopamine hydroxylase

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9
Q

Homogentisic acid oxidase

A

Catalyzes the degradation of tyrosine

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10
Q

Autosomal recessive disorder of tyrosine degradation caused by deficiency of homogentisic acid oxidase. Accumulation of large amounts of homogentisic acid. Connective tissue hyperpigmentation, degenerative joint disease.

A

Alkaptonuria

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11
Q

Depressed or absent tyrosinase activity leads to…

A

Albinism

tyrosine –> DOPA -(tyrosinase)-> dopaquinone

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12
Q

Conservative mutation

A

Missense mutation where one amino acid is replaced with another amino acid with similar biochemical characteristics

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13
Q

Deficiency of alpha-galactosidase A

A

Fabry disease

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14
Q

Accumulation of ceramide trihexoside

A

Fabry disease

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15
Q

Hypohidrosis, acroparesthesia, angiokeratomas… and without enzyme replacement, renal insufficiency and renal failure and death.

A

Fabry disease

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16
Q

Acroparesthesia

A

Episodic, debilitating, neuropathic pain in the extremities

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17
Q

Angiokeratoma

A

Punctate, dark red, nonblanching macule and papule that occur between umbilicus and knees

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18
Q

Acute leukemia is associated with which genetic disorders?

A 
Down syndrome
Patau syndrome
Ataxia telangiectasia
Bloom syndrome
Fanconi syndrome
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19
Q

Classic Galactosemia

A

Caused by impaired galactose-1-phosphate uridyl transferase (GALT) which converts Galactose 1P to UDP-galactose (transfers UDP from UDP-glucose)

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20
Q

Galactosyl beta-1, 4 glucose

A

Another name for lactose

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21
Q

Vomiting, lethargy, failure to thrive soon after breastfeeding is begun
Hyperchloremic metabolic acidosis, amino aciduria, impaired liver function.
Irreversible eye and liver damage from galactitol accumulation

A

Galactosemia

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22
Q

Galactokinase deficiency

A

Less severe; may cause cataracts?

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23
Q

PRPP synthetase gene increased activation

A

Leads to increased purine synthesis pathway and degradation –> increased gout risk.

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24
Q

What cells are responsible for the intense inflammatory response seen with gout?

A

Neutrophils - phagocytosis of urate crystals leads to release of various cytokines and inflammatory mediators that lead to further neutrophil activation and chemotaxis, resulting in a positive feedback loop that amplifies the inflammatory response.

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25
Q

What is the treatment for gout?

A

NSAIDs are first line because they inhibit prostanoid biosynthesis through COX2 I believe.

Colchicine - decreases tyrosine phosphorylation in response to monosodium urate, resulting in decreased neutrophil activation. Inhibits neutrophil chemotaxis and phagocytosis by preventing microtubule formation.

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26
Q

Growth hormone receptors act through what pathway?

A

JAK-STAT.
Attach to extracellular domain of growth homrone receptor –> dimerization –> conformation change of JAK –> tyrosine kinase activity –> STAT transcription activity

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27
Q

Vitamin deficiency after 4 years?

A

Cobalamin

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28
Q

How long does Vitamin A last?

A

6 months - contained in perisinusoidal stellate Ito cells of the liver

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29
Q

How long does folate last?

A

3-4 months, liver contains half of the body’s folate.

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30
Q

Vitamin K - how long does it last?

A

1-3 weeks.

31
Q

Lynch syndrome - HNPCC - which genes are mutated?

A

MutS or MutL

32
Q

Severe fatigue, splenomegaly (often causing early satiety/abdominal discomfort), hepatomegaly, anemia, bone marrow fibrosis

A

Primary myelofibrosis - JAK2 mutation

33
Q

Pruritis, erythromelalgia, splenomegaly, thrombotic complication, erythrocytosis, thrombocytosis

A

Polycythmia vera - JAK2 mutation

34
Q

Hemorrhagic and thrombotic symptoms (easy bruising, microangiopathic occlusion, thrombocytosis and megakaryocytic hyperplasia)

A

Essential thrombocytosis - JAK2 mutation

35
Q

Constitutional sx (fatigue, wt loss, excessive sweating), splenomegaly, leukocytosis with left shift (myelocytes, metamyelocytes, band forms)

A

BCR:ABL - CML

36
Q

JAK2 inhibitor approved for treatment of primary myelofibrosis

A

Ruxolitinib

37
Q

Valine –> Phenylalanine at 617 in JAK2

A

Constitutive tyrosine phosphorylation activity leading to the chronic myeloproliferative disorders

38
Q

15;17 translocation in acute promyelocytic leukemia

A

Leads to PML and retinoic acid receptor alpha fusion gene which blocks differentiation of myeloid precursors.

39
Q

EGF, PDGF, FGF signal through…

A

MAP Kinase - receptor autophosphorylates and triggers phosphorylation of ras

40
Q

First step in glycogen degradation

A

1,4 glycosidic linkage to form glucose-1-phosphate

41
Q

How do you convert pyruvate to PEP for gluconeogenesis?

A

pyruvate –> oxaloacetate through pyruvate carboxylase
oxaloacetate –> malate (malate dehydrogenase in mitochondria)
malate –> oxaloacetate (cytosolic malate dehydrogenase)
oxaloacetate –> PEP (phosphoenolpyruvate carboxykinase - PEPCK)

42
Q

What enzymes differ between glycolysis and gluconeogenesis?

A

pyruvate -> PEP
fructose 1,6 bisphosphatase (bypasses phosphofructokinase)
glucose-6-phosphatase (bypasses hexokinase)

43
Q

How do aminoglycosides work?

A

Impair INITIATION of protein synthesis and inhibit formation of INITIATION complex.
Bind 30S

44
Q

How do tetracyclines work?

A

Interfere with amino-acyl-tRNA binding to the A site

45
Q

Acetyl CoA carboxylase

A

Biotin dependent enzyme in liver and adipose tissue that catalyzes the first committed step in fatty acid synthesis, which occurs in the cytosol.

46
Q

Where does fatty acid oxidation occur?

Where does fatty acid synthesis occur?

A

Oxidation - Mitochondria

Synthesis - Cytosol

47
Q

Fetal hemoglobin

A

alpha 2 gamma 2

48
Q

Hemoglobin A2

A

alpha 2 delta 2

49
Q

earliest hemoglobin found in the fetus?

A

Hemoglobin gower, zeta 2 epsilon 2, synthesized in the yolk sac –> hemoglobin portland –> hemoglobin gower 2 –> hemoglobin F at 10-12 weeks

Wow!

50
Q

Hemoglobin Bart

A

4 gamma proteins (gamma 4).
Found in homozygous alpha thalassemia
High affinity for oxygen and does not release it to the tissues –> tissue hypoxia.

51
Q

NO comes from which AA?

A

Arginine (“Argh! NO!”)

52
Q

Urea comes from which AA?

A

Arginine + aspartate

53
Q

Heme comes from which AA?

A

Glycine + succinyl CoA

54
Q

Creatinine comes from what things?

A

Glycine + arginine + SAM

55
Q

GABA comes from which AA?

A

Glutamate

56
Q

Glutathione comes from which AA?

A

Glutamate

57
Q

Pyrimidines come from which AA?

A

Glutamate + aspartate

58
Q

Purines come from which AA?

A

Glutamate + aspartate + glycine (GAG)

59
Q

Niacin comes from which AA?

A

Tryptophan (“toe fan”)

60
Q

Thyroxine comes from which AA?

A

Tyrosine

61
Q

Melanin comes from which AA?

A

Tyrosine

62
Q

eNOS - endothelial nitric oxide synthase - synthesizes nitric oxide from what?

A

Arginine, NADPH, and O2

63
Q

Which processes occur outside the cell in collagen synthesis?

A

Terminal propeptides cleaved by N and C-procollagen peptidases.
Collagen molecules spontaneously assemble.
Covalent cross-links formed by lysyl oxidase.

64
Q

Pre-pro-alpha chain

A

Newly synthesized, unmodified alpha chain (first step in collagen synthesis)

65
Q

Pro-alpha chain

A

After hydrophobic signal peptide at N terminus is cleaved from the pre-pro-alpha chain (collagen formation)

66
Q

Procollagen molecule

A

Triple collagen helix which has had disulfide bond formation, hydroxylation of proline and lysine residues.

67
Q

Sideroblastic anemia enzyme

A

d-aminolevulinate synthase, requires B6

68
Q

Heme in liver versus heme in bone marrow

A

Liver –> used for cytochrome p450 system

Bone marrow –> used for hemoglobin

69
Q

AIP enzyme

A

Porphobilinogen deaminase

70
Q

Heme negatively feedback inhibits what?

A

ALA synthase

Reduction in heme synthesis leads to increased d-aminolevulinic acid and porphobilinogen which lead to acute abdominal pain and neurologic sx.

71
Q

What does lead inhibit?

A

ALA dehydradatase and ferrochelatase

72
Q

Zellweger syndrome

A

Infants are unable to properly form myelin in the CNS.

Hypotonia and seizures, hepatomegaly, mental retardation, early death within months

73
Q

Refsum disease

A

Defect in peroxisomal alpha oxidation –> neurological disturbances in response to accumulation of phytanic acid within the body. Strictly avoid chlorophyll in the diet.

74
Q

Where are very long chain fatty acids oxidized?

A

Peroxisomes

USMLE GAME TIME (46 decks)

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