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USMLE Step 1 > Biochemistry Metabolism > Flashcards

Biochemistry Metabolism Flashcards

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USMLE® Step 1 flashcards
1
Q

What processes occur in mitochondria?

A

Fatty acid oxidation (Beta oxidation), acetyl CoA production, TCA cycle, oxidative phosphorylation

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2
Q

What processes occur in cytoplasm?

A

glycolysis, FA synthesis, HMP shunt, protein synthesis (RER), steroid synthesis (SER), cholesterol synthesis

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3
Q

What processes require both cytoplasm and mitochondria:

A

HUG: heme synthesis, urea cycle, gluconeogenesis

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4
Q

kinase

A

uses ATP to add high energy phosphate

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5
Q

phosphorylase

A

adds inorganic phosphate w/out using ATP

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6
Q

phosphatase

A

removes phosphate group

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7
Q

dehydrogenase

A

catalyzes ox-redox reactions

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8
Q

hydroxylase

A

adds -OH group onto substrate

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9
Q

carboxylase

A

transfers CO2 group with help of biotin

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10
Q

mutase

A

relocates functional group within molecule

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11
Q

RDS: glycolysis

A

PFK-1; +: AMP, F26BP; -: ATP, citrate

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12
Q

RDS: gluconeogenesis

A

F16BPhosphatase; + ATP, acetyl-CoA; - AMP F26BP

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13
Q

RDS: TCA cycle

A

isocitrate dehydrogenase; + ADP; - ATP, NADH

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14
Q

RDS: glycogenesis

A

glycogen synthase; + G6P insulin, cortisol; - epinephrine, glucagon

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15
Q

RDS: glycogenolysis

A

glycogen phosphorylase; + epinephrine, glucagon, AMP; - G6P, insulin ATP

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16
Q

RDS: HMP shunt

A

G6PD; + NADP, - NADPH

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17
Q

RDS: de novo pyrimidine synthesis

A

Carbamoyl phosphate synthetase II

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18
Q

RDS: do novo purine synthesis

A

Glutamine-PRPP amidotransferase: -AMP, IMP, GMP

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19
Q

RDS: urea cycle

A

carbamoyl phosphate synthetase I: + n acetyl glutamate

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20
Q

RDS: fatty acid synthesis

A

acetyl-coa carboxlyase: + insulin, citrate; - glucagon, palmitoyl coA

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21
Q

RDS: fatty acid oxidation

A

carnitine acyltransferase: - malonyl coA

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22
Q

RDS: ketogenesis

A

HMG-coa synthase

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23
Q

RDS: cholesterol synthesis

A

HMG coA reductase: + insulin, thyroxin, - glucagon, cholesterol

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24
Q

which enzymes require biotin as a cofactor?

A

pyruvate carboxylase (pyruvate to OAA); acetyl coA to malonyl coA; propionyl COA to methylmalonyl COA

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25
Q

which enzymes require thiamine?

A

Transketolase (ribulose 5 phosphate to F6P); pyruvate DH (pyruvate to acetyl CoA); a-ketoglutarate DH (alphaKG to succinyl coA)

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26
Q

where is NADPH made? used?

A

product of HMP shunt; used in anabolic processes, respiratory burst, CYP450 system, glutathione reductase

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27
Q

hexokinase vs glucokinase

A

hexokinase in most tissues except liver/B cells of pancreas; low Km; high affinity; low Vmax and capacity; not induced by insulin; feedback inhibited by G6P; not associated with mature onset diabetes; glucokinase is opposite of hexokinase

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28
Q

galactokinase

A

galactose to galactose 1 phosphate; mild galactosemia

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29
Q

galactose 1 phophate uridyltransferase

A

glactose 1 phosphate to glucose 1 phosphate; severe galactosemia

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30
Q

aldolase A vs B

A

aldolase A–muscle, B–liver; glyceraldehyde 3 phosphate/DHAP to fructose 1,6 bisphosphate

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31
Q

hexokinase/glucokinase

A

Glucose to glucose 6 phosphate; irreversible

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32
Q

Glucose 6 phosphatase

A

glucose 6 phosphate to glucose; irreversible; von Gierke’s

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33
Q

G6PD

A

glucose 6 phosphate to 6 phosphogluconolactone; irreversible

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34
Q

transketolase

A

ribulose 5 phosphate to fructose 6 phosphate; requires thiamine

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35
Q

PFK-1

A

fructose 6 phosphate to F16BP; irreversible

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36
Q

Fructose 1,6 bisphosphatase

A

F16BP to F6P; irreversible

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37
Q

fructokinase

A

fructose to F1P; essential fructosuria

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38
Q

aldolase B

A

F1P to DHAP/glyceradehyde, fructose intolerance

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39
Q

pyruvate kinase

A

PEP to pyruvate; irreversible

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40
Q

pyruvate DH

A

pyruvate to acetyl coA; requires thiamine; irreversible

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41
Q

HMG coA reductase

A

HMG coA to mevalonate

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42
Q

pyruvate carboxylase

A

pyruvate to OAA; irreversible, requires biotin

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43
Q

PEP carboxykinase

A

OAA to PEP; irreversible

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44
Q

citrate synthase

A

OAA to citrate;

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45
Q

isocitrate dehydrogenase

A

isocitrate to alpha ketoglutarate; irreversible

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46
Q

alpha KG DH

A

a KG to succinyl coA; irreversible, requires thiamine

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47
Q

ornithine transcarbamoylase

A

ornithine + carbamoyl phosphate to citrulline

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48
Q

Which reactions in glycolysis produce ATP?

A

phosphoglycerate kinase (13BPG to 3 PG, reversible); pyruvate kinase (PEP to pyruvate, irreversible)

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49
Q

fasting state regulation by F26BP

A

increased glucagon–>increased cAMP–>increased protein kinase A–>increased FBPase2, decreased PFK2, less glycolysis

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50
Q

fed state regulation by F26BP

A

increased insulin–>decreased cAMP–>decreased PKA–>decreased FBPase2, increased PFK2, more glycolysis, less gluconeogenesis

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51
Q

pyruvate dehydrogenase complex requires which cofactors:

A

pyrophosphate (B1, thiamine, TPP); FAD (B2, riboflavin); NAD (B3, niacin); CoA (B5, pantothenate); lipoic acid

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52
Q

vomiting, rice water stools, garlic breath

A

arsenic poisoning, inhibits lipoic acid, disrupts pyruvate DH complex

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53
Q

purely ketogenic AAs

A

lysine, leucine

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54
Q

neurologic deficits, lactic acidosis, increased serum alanine since infancy

A

pyruvate dehydronase complex deficiency; buildup of pyruvate that gets shunted to lactate (via LDH) and alanine (via ALT); Tx with high intake of ketogenic nutrients

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55
Q

pyruvate can be shunted to 4 different pathways:

A

alanine amiotransferase (ALT) to alanine (requires B6); pyruvate carboxylase (requires biotin) to OAA (replenish TCA cycle or be used in gluconeogenesis); pyruvate DH (connect glycolysis to TCA cycle); LDH (requires B3)

56
Q

Rotenone

A

inhibits Complex I of ETC

57
Q

succinate dehydrogenase

A

part of TCA and Complex II of ETC

58
Q

Antimycin A

A

inhibits Complex III of ETC

59
Q

Cyanide, CO

A

inhibits complex IV of ETC

60
Q

oligomycin

A

inhibits complex V of ETC (ATP synthase)

61
Q

contains CoQ and cytochrome C

A

Complex III of ETC

62
Q

reduces oxygen to water in ETC

A

complex IV

63
Q

which side of mt membrane is proton gradient formed on?

A

proton gradient is formed in intermembrane space and flows through complex V on inner mt membrane to the mitochondrial matrix

64
Q

2,4 dinitrophenyl

A

increase permability of membrane; uncouple ETC, produces heat

65
Q

what are uncoupling agents?

A

2,4 dinitrophenyl, aspirin (fevers after OD), thermogenin in brown fat

66
Q

what reaction in gluconeogenesis requires GTP?

A

PEP carboxykinase (OAA to PEP)

67
Q

odd chain vs even chain fatty acids in gluconeogenesis

A

only odd chain fatty acids can participate; converted to proprionyl CoA and enter TCA as succinyl cOA; even chain FAs yield only acetyl CoA

68
Q

patients with CGD are at risk for what types of infection?

A

catalase + bugs: aspergillus, S aureus

69
Q

pyocyanin

A

released by pseudomonas aeruginosa to generate ROS to kill competing bacteria

70
Q

lactoferrin

A

protein found in secretory fluid and neutrophils that inhibits bacterial growth via iron chelation

71
Q

failure to track objects or develop a social smile

A

galactokinase deficiency; galactitol accumulates in lens–infantile cataracts

72
Q

failure to thrive,jaundice, hepatomegaly, infantile cataracts, retardation

A

classic galactosemia, uridyltransferase deficiency; tx by excluding galactose and lactose

73
Q

Schwann cells, retina, and kidneys lack what enzyme that makes them prone to damage by hyperglycemia

A

they have aldose reductase but lack sorbitol dehydrogenase, which results in accumulation of sorbitol->osmotic damage

74
Q

glucogenic essential amino acids:

A

methionine, valine, histidine

75
Q

glucogenic/ketogenic essential amino acids

A

isoleucine, phenylalanine, threonine, tryptophan

76
Q

Ketogenic essential amino acids

A

lysine, leucine

77
Q

which step of urea cycle requires N-acetyl glutamate as cofactor?

A

carbamoyl phosphate synthetase I (CO2 + NH3 to carbamoyl phosphate) requires 2 ATP; occurs in mitchondria

78
Q

which step of urea cycle generates AMP?

A

argininosuccinate synthetase: citrulline + aspartate to argininosuccinate requires ATP and generates AMP

79
Q

which step of urea cycle generates fumarate?

A

argininosuccinase: argininosuccinate to arginine generates fumarate

80
Q

which step of urea cycle generates urea?

A

arginase: arginine + H2O to ornithine and urea (to kidney)

81
Q

urea is comprised of what three things?

A

ammonia; carbon dioxide; aspartate; NH2-C=O-NH2

82
Q

ammonia is transported from muscle to liver how?

A

amino acids to glutamate to alanine–>bloodstream–>liver–>glutamate–>urea; pyruvate + NH3 = alanine; alpha KG + NH3 = glutamate

83
Q

urea cycle occurs mostly in?

A

liver; impaired in liver disease

84
Q

N-acetyl glutamate deficiency vs carbamoyl phosphate synthetase deficiency

A

NAG deficiency is AR, CPS is X linked recessive; both present identically: early in life, orotic acid elevated in blood and urine; decreased urea production; hyperammonemia; no megaloblastic anemia; increased ornithine with normal urea cycle enzymes suggests NAG deficiency

85
Q

carbamoyl phosphate synthetase deficiency vs orotic aciduria

A

orotic aciduria: UMP synthase (orotic acid to UMP) deficiency (de novo pyrimidine synthesis); no hyperammonemia; megaloblastic anemia

86
Q

Catecholamine synthesis pathway:

A

Phe–>Tyrosine–>Dopa–>Dopamine–>NE–>Epi-; cofactors required in order: BH4, BH4, B6, vitC, SAM; Enzymes: phenylalanine hydroxylase, tyrosine hydroxylase, dopa decarboxylase, dopamine hydroxlyase,

87
Q

Tyrosine can form what three products:

A

Dopa or Thyroxine, homogentisic acid

88
Q

DOPA can form what two products:

A

Melanin or Dopamine

89
Q

tryptophan forms which AAs

A

niacin (requires B6) to NAD/NADP+, serotonin (requires BH4 and B6); serotonin to melatonin

90
Q

histidine forms which AAs

A

histamine (requires B6)

91
Q

Glycine forms which amino acids

A

porphyrin (requires B6)–>Heme

92
Q

Glutamate forms which amino acids

A

GABA (requires B6); glutathione

93
Q

Arginine forms which AAs

A

creatine, urea, Nitric oxide (requires BH4)

94
Q

Phenlyketonuria can be caused by:

A

deficiency in phenylalanine hydroxylate or BH4 (malignant PKU); Tx by reducing Phe intake and increased tyrosine intake

95
Q

maternal PKU

A

infant microcephaly, intellectual deficiency, growth retardation, congenital heart defect

96
Q

alkaptonuria

A

AR deficiency of homogentisate oxidate in degradative pathway of tyrosine to fumarate

97
Q

dark connective tissue, brown sclerae, urine turns black on prolonged air, may have debilitating arthralgias

A

alkaptonuria–homogentisate oxidate deficiency; AR; homogentisate acid buildup in cartilage

98
Q

albinism

A

tyrosinase deficiency–cannot convert DOPA to melanin

99
Q

inhibits DOPA decarboxylase

A

carbidopa

100
Q

3 deficiencies resulting in homocystinuria

A

cystathione synthase deficiency (Tx by decreasing methionine, increasing cysteine, increase B12 and folate in diet); decreased affinity of cystathione synthase for pyridoxal phosphate (increase B6 and cysteine in diet); Homocystein methyltransferase deficiency (increase methionine in diet)

101
Q

homocystinuria vs marfans?

A

marfans has negative nitroprusside test. lens up and out in marfans; homocystinuira lens down and in;

102
Q

cystinuria

A

defect of renal PCT COLA transporter (cysteine, ornithine, lysine, arginine); excess cystine in urine–>hexagonal uric acid stones; AR; nitroprusside test positive; Tx with urinary alkalinization (potassium citrate, acetazolamide) and chelating agents, hydration

103
Q

urine smells like burnt sugar

A

MSUD: blocked degradation of ILV (isoleucine, leucine, valine) due to decreased alpha-ketoacid dehydrogenase (B1); Tx AA restriction with B1 supplementation;

104
Q

Glycogen phosphorylase vs glycogen synthase

A

phosphorylase (glycogen to glucose) is activated by glycogen phosphorylase kinase (via glucagon, epinephine and PKA and calcium); synthase (glucose to glycogen) is activated by insulin; PKA inhibits synthase; protein phosphatase inhibits phosphorylase

105
Q

severe fasting hypoglycemia, increased glycogen in liver, high blood lactate, hepatomegaly

A

Type I glycogen storage disease (von Gierke); glucose 6 phosphatase defect–>cant release glucose from liver into bloodstream; tx with frequent carbs, avoid fructose and galactose (both are converted to glucose 6 P)

106
Q

cardiomyopathy and systemic findings–>early death

A

Type 2 GSD (Pompe disease); lysosomal alpha 1,4 glucosidase (acid maltase) deficiency;

107
Q

milder hypoglycemia, normal blood lactate levels

A

Type 3 (Cori disease); debranching enzyme (alpha 1,6 glucosidase); intact gluconeogenesis just can’t utilize all of glycogen

108
Q

increased glycogen in muscle, painful muscle cramps, myoglobinuria (red urine) with strenous exercise, arhythmia from electrolyte disturbances

A

Type V (McArdle disease); skeletal muscle glycogen phosphorylase (myophosphorylase); can’t break down glycogen in muscle

109
Q

all glycogen storage disease are inherited in what fashion?

A

AR

110
Q

peripheral neuropathy of hands/feet, angiokeratomas, cardiovascular/renal disease

A

Fabry disease; alpha galactosidase A, accumulation of ceramide trihexoside; XR

111
Q

HSM, pancytopenia, aseptic necrosis of femur/bone crises, lipid laden macrophages,

A

Gaucher disease, glucocerebrosidase (beta glucosidas), accumulation of glucocerebroside, AR

112
Q

progressive neurodegeneration, HSM, cherry red spot on macula, foam cells (lipid laden macrophages)

A

Niemann Pick disease; sphingomyelinase; accumuation of sphingomyelin, AR

113
Q

progressive neurodegeneration, developmental delay, cherry red spot on macula, lysosome with onion skin, no HSM

A

Tay Sachs, hexosaminidase A, GM2 ganglioside accumulation, AR

114
Q

Peripheral neuropathy, developmental delay, optic atrophy, globoid (multinucleated) cells

A

Krabbe disease, Beta galactosidase (galactocerebrosidase); galactocerebroside/psychosine; AR

115
Q

central and peripheral demyelination with ataxia, dementia

A

metachromatic leukodystrophy; arylsulfatase A; cerebroside sulfate, AR

116
Q

developmental delay, gargolyism, airway obstruction, corneal clouding, HSM

A

Hurler syndrome; alpha L iduronidase; heparan sulfate, dermatan sulfate, AR

117
Q

Mild hurler + aggressive behavior, no corneal clouding

A

Hunter Syndrome; iduronate sulfatase; heparan sulfate/dermatan sulfate; XR

118
Q

Which sphingolipidoses LSD is XR?

A

Fabry’s all others are AR

119
Q

Which mucopolysaccharidoses is XR?

A

hunter’s; hurlers is AR

120
Q

weakness, hypotonia, hypoketotic hypoglycemia

A

carnitine deficiency (cannot transport LCFAs into mitochondria, toxic accumulation of FAs)

121
Q

acyl-coA deficiency

A

increased dicarboxylic acids, decreased glucose and ketones, acetyl coA is + allosteric regulator of pyruvate carboxylase in gluconeogenesis; decreased acetyl CoA, decreased fasting glucose

122
Q

ketone bodies

A

acetoacetate and B-hydroxybutyrate; urine test does not detect B hydroxybutyrate

123
Q

ketone bodies cannot be utilized as fuel where?

A

liver (no thiotransferase); RBCs (no mitochondria); renal medulla (not enough oxidative capacity)

124
Q

pancreatic lipase

A

degradation of dietary TGs in small intestine

125
Q

lipoprotein lipase

A

degradation of TGs circulating in chylomicrons and VLDLs, found on vascular endothelial cell surface; activated by insulin

126
Q

hepatic TG lipase

A

degradation of TG remaining in IDL

127
Q

hormone sensitive lipase

A

degradation of TGs stored in adipocytes

128
Q

LCAT

A

esterifies cholesterol (nascent HDL to mature HDL)

129
Q

CETP

A

transfer of cholesterol esters from HDL to VLDL/IDL/LDL

130
Q

chylomicrons vs VLDL

A

chylomicrons carry TGs from food to peripheral tissues. VLDL carries endogenous TGs from the liver; chylomicrons: ApoB48, VLDL ApoB100

131
Q

lipoprotein lipase cofactor

A

ApoCII

132
Q

mediates remnant uptake

A

ApoE

133
Q

activates LCAT

A

Apo A-I

134
Q

mediates chylomicron secretion

A

B-48

135
Q

binds LDL receptor

A

B-100

USMLE Step 1 (36 decks)

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