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

Biochemistry - Part 2 - More important concepts 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
What is the treatment for gout?
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.
26
Growth hormone receptors act through what pathway?
JAK-STAT. Attach to extracellular domain of growth homrone receptor --> dimerization --> conformation change of JAK --> tyrosine kinase activity --> STAT transcription activity
27
Vitamin deficiency after 4 years?
Cobalamin
28
How long does Vitamin A last?
6 months - contained in perisinusoidal stellate Ito cells of the liver
29
How long does folate last?
3-4 months, liver contains half of the body's folate.
30
Vitamin K - how long does it last?
1-3 weeks.
31
Lynch syndrome - HNPCC - which genes are mutated?
MutS or MutL
32
Severe fatigue, splenomegaly (often causing early satiety/abdominal discomfort), hepatomegaly, anemia, bone marrow fibrosis
Primary myelofibrosis - JAK2 mutation
33
Pruritis, erythromelalgia, splenomegaly, thrombotic complication, erythrocytosis, thrombocytosis
Polycythmia vera - JAK2 mutation
34
Hemorrhagic and thrombotic symptoms (easy bruising, microangiopathic occlusion, thrombocytosis and megakaryocytic hyperplasia)
Essential thrombocytosis - JAK2 mutation
35
Constitutional sx (fatigue, wt loss, excessive sweating), splenomegaly, leukocytosis with left shift (myelocytes, metamyelocytes, band forms)
BCR:ABL - CML
36
JAK2 inhibitor approved for treatment of primary myelofibrosis
Ruxolitinib
37
Valine --> Phenylalanine at 617 in JAK2
Constitutive tyrosine phosphorylation activity leading to the chronic myeloproliferative disorders
38
15;17 translocation in acute promyelocytic leukemia
Leads to PML and retinoic acid receptor alpha fusion gene which blocks differentiation of myeloid precursors.
39
EGF, PDGF, FGF signal through...
MAP Kinase - receptor autophosphorylates and triggers phosphorylation of ras
40
First step in glycogen degradation
1,4 glycosidic linkage to form glucose-1-phosphate
41
How do you convert pyruvate to PEP for gluconeogenesis?
pyruvate --> oxaloacetate through pyruvate carboxylase oxaloacetate --> malate (malate dehydrogenase in mitochondria) malate --> oxaloacetate (cytosolic malate dehydrogenase) oxaloacetate --> PEP (phosphoenolpyruvate carboxykinase - PEPCK)
42
What enzymes differ between glycolysis and gluconeogenesis?
pyruvate -> PEP fructose 1,6 bisphosphatase (bypasses phosphofructokinase) glucose-6-phosphatase (bypasses hexokinase)
43
How do aminoglycosides work?
Impair INITIATION of protein synthesis and inhibit formation of INITIATION complex. Bind 30S
44
How do tetracyclines work?
Interfere with amino-acyl-tRNA binding to the A site
45
Acetyl CoA carboxylase
Biotin dependent enzyme in liver and adipose tissue that catalyzes the first committed step in fatty acid synthesis, which occurs in the cytosol.
46
Where does fatty acid oxidation occur? | Where does fatty acid synthesis occur?
Oxidation - Mitochondria | Synthesis - Cytosol
47
Fetal hemoglobin
alpha 2 gamma 2
48
Hemoglobin A2
alpha 2 delta 2
49
earliest hemoglobin found in the fetus?
Hemoglobin gower, zeta 2 epsilon 2, synthesized in the yolk sac --> hemoglobin portland --> hemoglobin gower 2 --> hemoglobin F at 10-12 weeks Wow!
50
Hemoglobin Bart
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
NO comes from which AA?
Arginine ("Argh! NO!")
52
Urea comes from which AA?
Arginine + aspartate
53
Heme comes from which AA?
Glycine + succinyl CoA
54
Creatinine comes from what things?
Glycine + arginine + SAM
55
GABA comes from which AA?
Glutamate
56
Glutathione comes from which AA?
Glutamate
57
Pyrimidines come from which AA?
Glutamate + aspartate
58
Purines come from which AA?
Glutamate + aspartate + glycine (GAG)
59
Niacin comes from which AA?
Tryptophan ("toe fan")
60
Thyroxine comes from which AA?
Tyrosine
61
Melanin comes from which AA?
Tyrosine
62
eNOS - endothelial nitric oxide synthase - synthesizes nitric oxide from what?
Arginine, NADPH, and O2
63
Which processes occur outside the cell in collagen synthesis?
Terminal propeptides cleaved by N and C-procollagen peptidases. Collagen molecules spontaneously assemble. Covalent cross-links formed by lysyl oxidase.
64
Pre-pro-alpha chain
Newly synthesized, unmodified alpha chain (first step in collagen synthesis)
65
Pro-alpha chain
After hydrophobic signal peptide at N terminus is cleaved from the pre-pro-alpha chain (collagen formation)
66
Procollagen molecule
Triple collagen helix which has had disulfide bond formation, hydroxylation of proline and lysine residues.
67
Sideroblastic anemia enzyme
d-aminolevulinate synthase, requires B6
68
Heme in liver versus heme in bone marrow
Liver --> used for cytochrome p450 system | Bone marrow --> used for hemoglobin
69
AIP enzyme
Porphobilinogen deaminase
70
Heme negatively feedback inhibits what?
ALA synthase Reduction in heme synthesis leads to increased d-aminolevulinic acid and porphobilinogen which lead to acute abdominal pain and neurologic sx.
71
What does lead inhibit?
ALA dehydradatase and ferrochelatase
72
Zellweger syndrome
Infants are unable to properly form myelin in the CNS. | Hypotonia and seizures, hepatomegaly, mental retardation, early death within months
73
Refsum disease
Defect in peroxisomal alpha oxidation --> neurological disturbances in response to accumulation of phytanic acid within the body. Strictly avoid chlorophyll in the diet.
74
Where are very long chain fatty acids oxidized?
Peroxisomes

USMLE GAME TIME (46 decks)

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