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USMLE 1 > Biochemistry- Metabolism > Flashcards

Biochemistry- Metabolism Flashcards

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USMLE® Step 1 flashcards
1
Q

Metabolism sites

Mitochondria

A

Fatty acid oxidation (β-oxidation), acetyl- CoA production, TCA cycle, oxidative phosphorylation, ketogenesis.

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2
Q

Metabolism sites

Cytoplasm Glycolysis

A

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

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3
Q

Metabolism sites

Both

A

Heme synthesis, Urea cycle, Gluconeogenesis. HUGs take two (ie, both).

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4
Q

Enzyme terminology

A 
Kinase
Phosphorylase
Phosphatase
Dehydrogenase
Hydroxylase
Carboxylase
Carboxylase
Synthase/synthetase
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5
Q 
Rate-determining enzymes of metabolic processes
Glycolysis
Gluconeogenesis
TCA cycle
Glycogenesis
Glycogenolysis
HMP shunt
A 
Phosphofructokinase-1 (PFK-1)
Fructose-1,6-bisphosphatase
Isocitrate dehydrogenase
Glycogen synthase
Glycogen phosphorylase
Glucose-6-phosphate dehydrogenase (G6PD)
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6
Q 
Rate-determining enzymes of metabolic processes
De novo pyrimidine synthesis
De novo purine synthesis
Urea cycle
Fatty acid synthesis
Fatty acid oxidation
Ketogenesis
Cholesterol synthesis
A
  • Carbamoyl phosphate synthetase II
  • Glutamine-phosphoribosylpyrophosphate (PRPP) amidotransferase
  • Carbamoyl phosphate synthetase I
  • Acetyl-CoA carboxylase (ACC)
  • Carnitine acyltransferase I
  • HMG-CoA synthase
  • HMG-CoA reductase
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7
Q

Arsenic causes glycolysis to…

A

produce zero net ATP.

Arsenic poisoning clinical findings: vomiting, rice-water stools, garlic breath, QT prolongation.

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8
Q 
Activated carriers: 
ATP 
NADH, NADPH, FADH2 
CoA, lipoamide 
Biotin 
Tetrahydrofolates
S-adenosylmethionine (SAM) 
TPP
A 
Phosphoryl groups
Electrons
Acyl groups
CO2
 1-carbon units
CH3 groups
Aldehydes
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9
Q

NADPH is used in:

A

􀂃 Anabolic processes
􀂃 Respiratory burst
􀂃 Cytochrome P-450 system
􀂃 Glutathione reductase

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10
Q

NAD+ is generally used in…

NADPH is used in…

A

Catabolic processes to carry reducing equivalents away as NADH.

Anabolic processes (steroid and fatty acid synthesis) as a supply of reducing equivalents.

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11
Q 
Hexokinase :
Location 
Km 
Vmax
Induced by insulin 
Feedback-inhibited by glucose-6-phosphate
A 
Most tissues, except liver and pancreatic β cells.
 Lower (higher affinity)
 Lower (lower capacity) 
No
Yes
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12
Q 
Glucokinase:
Location 
Km 
Vmax
Induced by insulin 
Feedback-inhibited by glucose-6-phosphate
A 
Liver, β cells of pancreas.
Higher (lower affinity)
Higher (higher capacity)
Yes
No
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13
Q

Glycolysis regulation, key enzymes

A

Hexokinase/glucokinase
Phosphofructokinase-1
Phosphoglycerate kinase
Pyruvate kinase

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14
Q

Regulation by fructose-2,6- bisphosphate

A

FBPase-2 (fructose bisphosphatase-2) and PFK-2 (phosphofructokinase-2) are the same bifunctional
enzyme whose function is reversed by phosphorylation by protein kinase A.

Fasting state: FBPase-2
Fed state: PFK-2

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15
Q

Pyruvate dehydrogenase complex

A

The Lovely Co-enzymes For Nerds:

  1. Thiamine pyrophosphate (B1)
  2. Lipoic acid (inhibited by arsenic)
  3. CoA (B5, pantothenic acid)
  4. FAD (B2, riboflavin)
  5. NAD+ (B3, niacin)
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16
Q

Pyruvate dehydrogenase complex deficiency

Findings

TREATMENT

A

pyruvate that gets shunted to lactate (via LDH) and alanine (via ALT). X-linked.

Neurologic defects, lactic acidosis, higher serum
alanine starting in infancy.

Lysine and Leucine—the onLy pureLy ketogenic
amino acids.

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17
Q

Functions of different pyruvate metabolic

pathways (and their associated cofactors):

A 
Alanine aminotransferase (B6)
Pyruvate carboxylase (biotin)
Pyruvate dehydrogenase (B1, B2, B3, B5, lipoic acid)
Lactic acid dehydrogenase (B3)
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18
Q

TCA cycle (Krebs cycle)

A

Citrate Is Krebs’ Starting Substrate For Making
Oxaloacetate:

Citrato, Isocitrato, alfaKetoglutarato, Succinil coa, Succinato, malato, Fumarato, Oxalato.

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19
Q

Electron transport chain and oxidative phosphorylation

A

NADH electrons from glycolysis enter mitochondria via the malate-aspartate or glycerol-3-phosphate shuttle.

FADH2 electrons are transferred to complex II (succinato deshidrogenasa)

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20
Q

Electron transport inhibitors

A

RotenONE: complex ONE inhibitor.
“An-3-mycin” (antimycin) A: complex 3 inhibitor.
CO/CN: complex 4 inhibitors (4 letters).

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21
Q

ATP synthase inhibitors

A

Oligomycin

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22
Q

Uncoupling agents: ATP synthesis stops, but electron transport continues. Produces heat.

A

2,4-Dinitrophenol (used illicitly for weight

loss), aspirin, thermogenin.

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23
Q

Gluconeogenesis, irreversible enzymes

A

Pathway Produces Fresh Glucose.

Piruvato carboxilasa
Phosphoenolpiruvato carboxicinasa
Fructosa 1-6 bifosfatasa
Glucosa 6 fosfatasa

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24
Q

HMP shunt (pentose phosphate pathway)
FUNTCTION
REACTIONS

A

Provides a source of NADPH.
Yields ribose for nucleotide synthesis and glycolytic intermediates.

Oxidative (irreversible): Glucose-6-P dehydrogenase

NonOxidative (reversible): Phosphopentose isomerase,
transketolases (B1).

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25
Q

Glucose-6-phosphate dehydrogenase deficiency

A

X-linked recessive disorder; most common human enzyme deficiency.

Heinz bodies—denatured Hemoglobin precipitates within RBCs. Bite cells—result from the phagocytic removal of Heinz bodies by splenic macrophages.

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26
Q

Essential fructosuria

A

Defect in fructokinase. Autosomal recessive. A benign, asymptomatic condition.
Symptoms: fructose appears in blood and urine.

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27
Q

Fructose intolerance

A

Hereditary deficiency of aldolase B. Autosomal recessive. Fructose-1-phosphate accumulates, results in inhibition of glycogenolysis and gluconeogenesis.

Symptoms following consumption of fruit, juice, or honey: hypoglycemia, jaundice, cirrhosis, vomiting.

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28
Q

Galactokinase deficiency

A

deficiency of galactokinase. Galactitol accumulates. mild condition. Autosomal recessive

Galactosemia and galactosuria; infantile cataracts.

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29
Q

Classic galactosemia

A

Absence of galactose-1-phosphate uridyltransferase. Autosomal recessive.

Begins feeding and include failure to thrive, jaundice, hepatomegaly, infantile cataracts, intellectual disability. Can predispose to E coli sepsis in neonates.

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30
Q

Fructose is to Aldolase B as Galactose is to

UridylTransferase (FAB GUT).

A

Fructose intolerance

Classic galactosemia

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31
Q

Sorbitol synthesis and enzyme location

A

Aldose reductase and Sorbitol dehydrogenase.

Lens has primarily aldose reductase. Retina, Kidneys, and Schwann cells have only aldose reductase (LuRKS).

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32
Q

Amino acids

Essential

A

Glucogenic: methionine (Met), histidine (His),
valine (Val). “I met his valentine, she is so sweet (glucogenic)”.

Glucogenic/ketogenic: isoleucine (Ile), phenylalanine (Phe), threonine (Thr), tryptophan (Trp).

Ketogenic: leucine (Leu), lysine (Lys)

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33
Q

Basic

A

His lys (lies) are basic:

Histidine (His), lysine (Lys), arginine (Arg).
Arg is most basic

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34
Q

Acidic

A

Aspartic acid (Asp) and glutamic acid (Glu).

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35
Q

Urea cycle

A

Excess nitrogen generated by Amino acid catabolism is converted to urea and excreted by the kidneys.

Ordinarily, Careless Crappers Are Also
Frivolous About Urination:

Ornitina
Carbamoil fosfato
Citrulina
Aspartato
Argininosuccinato
Fumarato
Arginina
Urea
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36
Q

Hyperammonemia

A

Can be acquired (eg, liver disease) or hereditary
(eg, urea cycle enzyme deficiencies).

tremor (asterixis), slurring of speech, somnolence, vomiting, cerebral edema, blurring of vision.

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37
Q

May be given to reduce ammonia levels:

A
  • Lactulose to acidify the GI tract and trap
    NH4 + for excretion.
  • Antibiotics (eg, rifaximin) to reduce colonic
    ammoniagenic bacteria.
  • Benzoate, phenylacetate, or phenylbutyrate react with glycine or glutamine, forming products that are renally excreted.
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38
Q

Ornithine transcarbamylase deficiency

A

X-linked recessive. Interferes with the body’s ability to eliminate ammonia. Often evident in the first few days of life.

Higher orotic acid in blood and urine, Decreased BUN, symptoms of hyperammonemia.

39
Q

Amino acid derivatives:

Phenylalanine

A

BH4… Tyrosine + BH4… Dopa + B6… Dopamine + Vitaminca C… Norepinefrina + SMA… Epinefrina

40
Q

Amino acid derivatives:

Tryptophan

A

B2 + B6… Niacin

BH4 + B6… Serotonina… Melatonina

41
Q

Amino acid derivatives:
Histidine

Glycine

A

B6… Histamine

B6… porfirina

42
Q

Amino acid derivatives:

Glutamate

A

B6… GABA

Glutation

43
Q

Amino acid derivatives:

Arginine

A

Creatinina
Urea
BH4… Oxido nítrico

44
Q

Albinism mutation

A

Mutación en la tirosinasa

DOPA + Tirosinasa = Melanina

45
Q

Carbidopa

A

inhibits DOPA decarboxylase

46
Q

Phenylketonuria (PKU)

A

Phenylalanine hydroxylase or tetrahydrobiopterin (BH4)

Autosomal recessive

Findings: intellectual disability, growth retardation, seizures, fair skin, eczema, musty body odor.

47
Q

Maternal PKU

A

lack of proper dietary therapy during pregnancy.

Findings in infant: microcephaly, intellectual disability, growth retardation, congenital heart defects.

48
Q

Maple syrup urine

disease

A

Autosomal recessive

Blocked degradation of branched amino acids (Isoleucine, Leucine, Valine) due to branched-chain α-ketoacid dehydrogenase (B1).

Causes severe CNS defects, intellectual disability, and death.

49
Q

Alkaptonuria

A

Autosomal recessive. Deficiency of homogentisate oxidase in the degradative pathway of tyrosine to fumarate.

Findings: bluish-black connective tissue, ear cartilage, and sclerae (ochronosis); urine turns black on prolonged exposure to air. May have debilitating arthralgias (homogentisic acid toxic to cartilage).

50
Q

Homocystinuria

Types

A

(all autosomal recessive):
Cystathionine synthase deficiency

Reduced affinity of cystathionine synthase for
pyridoxal phosphate.

Methionine synthase deficiency

51
Q

Homocystinuria findings

A

HOMOCYstinuria:

  • Homocysteine in urine
  • Osteoporosis
  • Marfanoid habitus
  • Ocular changes
  • Cardiovascular effects
  • kYphosis
  • intellectual disability.
52
Q

Cystinuria

A

Defect of renal PCT and intestinal amino acid transporter that prevents reabsorption of Cystine, Ornithine, Lysine, and Arginine (COLA).

Autosomal recessive. Common (1:7000).
Urinary cyanide-nitroprusside test is diagnostic.

53
Q

Glycogen storage diseases

A

Periodic acid–Schiff stain identifies glycogen and is useful in identifying these diseases.

“Very Poor Carbohydrate Metabolism”.
Types I, II, III, and V are autosomal recessive.

Von Gierke
Pompe
Cori
McArdle

54
Q

Von Gierke disease

type I

A

Glucose-6-phosphatase deficiency

Severe fasting hypoglycemia, aumented Glycogen in liver, higher blood lactate, higher triglycerides, higher uric acid (Gout), and hepatomegaly.

55
Q 
Pompe disease
(type II)
A

PomPe trashes the PumP (1,4) (heart, liver, and muscle).

Lysosomal acid α-1,4- glucosidase (acid maltase)

Cardiomegaly, hypertrophic cardiomyopathy, hypotonia,
exercise intolerance, and systemic findings lead to early
death.

56
Q 
Cori disease
(type III)
A

Debranching enzyme (α-1,6-glucosidase)

Milder form of von Gierke (type I) with normal blood
lactate levels.

57
Q 
McArdle disease
(type V)
A

Skeletal muscle glycogen phosphorylase (Myophosphorylase).

Higher Glycogen in muscle, but muscle cannot break it down, painful Muscle cramps, Myoglobinuria (red urine)
with strenuous exercise, and arrhythmia from electrolyte
abnormalities.

58
Q

Lysosomal storage diseases

Tay-Sachs disease

A 
HeXosaminidase A (“TAy-SaX”). AR. 
GM2 ganglioside accumulates.

Neurodegeneration, developmental delay, “cherry-red”
spot on macula, lysosomes with onion skin, no hepatosplenomegaly (vs Niemann-Pick).

59
Q

Lysosomal storage diseases

Fabry disease

A

α-galactosidase A. XR.
Ceramide trihexoside accumulates.

Early: Triad of episodic peripheral neuropathy, angiokeratomas, hypohidrosis.

60
Q

Lysosomal storage diseases

Metachromatic leukodystrophy

A

Arylsulfatase A. AR.
Cerebroside sulfate accumulates.

Central and peripheral demyelination with ataxia, dementia.

61
Q

Lysosomal storage diseases

Krabbe disease

A

Galactocerebrosidase.AR.
Galactocerebroside, psychosine accumulates.

Peripheral neuropathy, destruction of oligodendrocytes, developmental delay, optic atrophy, globoid cells.

62
Q

Lysosomal storage diseases

Gaucher disease

A

Most common. Glucocerebrosidase (β-glucosidase); AR.
Glucocerebroside accumulates.

Hepatosplenomegaly, pancytopenia, osteoporosis, avascular necrosis of femur, bone crises, Gaucher cells.

63
Q

Lysosomal storage diseases

Niemann-Pick disease

A

Sphingomyelinase. AR.
Sphingomyelin accumulates.

Progressive neurodegenera tion, hepatosplenomegaly, foam cells (lipid-laden macrophages), “cherry-red” spot on macula.

64
Q

Mucopolysaccharidoses

Hurler syndrome

A

α-l-iduronidase. AR.
Heparan sulfate, dermatan sulfate accumulates.

Developmental delay, gargoylism, airway obstruction, corneal clouding, hepatosplenomegaly.

65
Q

Mucopolysaccharidoses

Hunter syndrome

A

Iduronate sulfatase. XR.
Heparan sulfate, dermatan sulfate accumulates.

Mild Hurler + aggressive behavior, no corneal clouding.

66
Q

Higher incidence of Tay-Sachs, Niemann-Pick, and

some forms of Gaucher disease in…

A

Ashkenazi

Jews.

67
Q

Fatty acid synthesis requires…

A

“SYtrate” = SYnthesis.

Transport of citrate from mitochondria to cytosol.

68
Q

Long-chain fatty acid (LCFA) degradation requires…

A

CARnitine = CARnage of fatty acids.

carnitine-dependent transport into the mitochondrial matrix.

69
Q

Systemic 1° carnitine deficiency

A

inherited defect in transport of LCFAs into the
mitochondria and toxic accumulation.

Causes weakness, hypotonia, and hypoketotic hypoglycemia.

70
Q

Medium-chain acyl-CoA dehydrogenase

deficiency

A

lower ability to break down fatty acids into acetyl-CoA accumulation of fatty acyl carnitines in the blood with hypoketotic hypoglycemia.

Causes vomiting, lethargy, seizures, coma, liver dysfunction. Can lead to sudden death in infants or children.

Treat by avoiding fasting.

71
Q

Ketogenesis

A

In prolonged starvation and diabetic ketoacidosis, oxaloacetate is depleted for gluconeogenesis.

In alcoholism, excess NADH shunts oxaloacetate to malate.

Both processes cause a buildup of acetyl-CoA, which shunts glucose and FFA toward the production of ketone bodies.

72
Q

Ketone bodies:

A

acetone, acetoacetate, β-hydroxybutyrate.

Urine test for ketones can detect acetoacetate, but not β-hydroxybutyrate.

73
Q

Fed state (after a meal).

A

Glycolysis and aerobic respiration.

74
Q

Fasting (between meals)

A

Hepatic glycogenolysis (major); hepatic gluconeogenesis, adipose release of FFA (minor).

75
Q

Starvation days 1–3

A

􀂃 Hepatic glycogenolysis
􀂃 Adipose release of FFA
􀂃 Muscle and liver, which shift fuel use from glucose to FFA.
􀂃 Hepatic gluconeogenesis from peripheral tissue lactate and alanine, and from adipose tissue glycerol and propionyl-CoA (from odd-chain FFA—the only
triacylglycerol components that contribute to gluconeogenesis)

76
Q

Starvation after day 3

A

Adipose stores (ketone bodies become the main source of energy for the brain).

After these are depleted, vital protein degradation accelerates, leading to organ failure and death.

*Glycogen reserves depleted after day 1.

77
Q

kcal
1g carb =
1g alcohol =
1g fatty acid =

A

4 kcal
7 kcal
9 kcal

78
Q

Lipoprotein lipase (LPL)

A

Degradation of TGs circulating in chylomicrons and VLDLs. Found on vascular endothelial surface.

79
Q

Hepatic TG lipase (HL)

A

degradation of TGs remaining in IDL.

80
Q

Hormone-sensitive lipase

A

degradation of TGs stored in adipocytes.

81
Q

LCAT

A

catalyzes esterification of 2⁄3 of plasma cholesterol.

82
Q

Cholesterol ester transfer protein (CETP)

A

mediates transfer of cholesterol esters to other

lipoprotein particles.

83
Q

Apolipoprotein E

A

Mediates remnant uptake (Everything Except LDL).

84
Q

Apolipoprotein A-I

A

Activates LCAT

85
Q

Apolipoprotein C-II

A

Lipoprotein lipase Cofactor that Catalyzes Cleavage

86
Q

Apolipoprotein B-48

A

Mediates chylomicron secretion into lymphatics

87
Q

Apolipoprotein B-100

A

Binds LDL receptor

88
Q

LDL

HDL

VLDL

IDL

A

transports cholesterol from liver to tissues.

transports cholesterol from periphery to
liver.

Delivers hepatic TGs to peripheral tissue.

Formed in the degradation of VLDL. Delivers TGs and cholesterol to liver.

89
Q

Abetalipoproteinemia

A

Autosomal recessive. Chylomicrons, VLDL, LDL absent. Deficiency in ApoB48, ApoB100.

Severe fat malabsorption, steatorrhea, failure to thrive.

Late manifestations include retinitis pigmentosa, spinocerebellar degeneration due to vitamin E
deficiency, progressive ataxia, acanthocytosis.

90
Q

Familial dyslipidemias

I—Hyperchylomicronemia

A

AR. Lipoprotein lipase or apolipoprotein C-II deficiency.
Higher Chylomicrons, TG, cholesterol.

Pancreatitis, hepatosplenomegaly, and eruptive/pruritic xanthomas (no 􀁱 risk for atherosclerosis).
Creamy layer in supernatant.

91
Q

Familial dyslipidemias

II—Familial hypercholesterolemia

A

AD. Absent or defective LDL receptors.
IIa: higher LDL, cholesterol
IIb:higher LDL, cholesterol, VLDL

Heterozygotes (1:500) have cholesterol ≈ 300mg/dL;
homozygotes (very rare) have cholesterol ≈ 700+ mg/dL.

Accelerated atherosclerosis (may have MI before age 20), tendon (Achilles) xanthomas, and corneal arcus.

92
Q

Familial dyslipidemias

III—Dysbetalipoproteinemia

A

AR. Defective ApoE.
higher Chylomicrons, VLDL.

Premature atherosclerosis, tuberoeruptive xanthomas,
xanthoma striatum palmare.

93
Q

Familial dyslipidemias

IV—Hypertriglyceridemia

A

AD. Hepatic overproduction of VLDL.
Higher VLDL, TG.

Hypertriglyceridemia (> 1000 mg/dL) can cause acute pancreatitis.

USMLE 1 (73 decks)

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