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USMLE Buzzwords - WLB > Biochem - WLB > Flashcards

Biochem - WLB Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the rate-limiting enzyme in purine synthesis?

A

Glutamine PRPP Amidotransferase

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2
Q

What is the rate-limiting enzyme in pyrimidine synthesis?

A

Carbamoyl phosphate synthetase II (CPS-2)

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3
Q

What are the sources of carbon in the synthesis of purines?

A

CO2 + Glycine + THF

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4
Q

What are the sources of carbon in the synthesis of pyrimidines?

A

CO2 + Aspartate

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5
Q

Which medication inhibits ribonucleotide reductase?

A

Hydroxyurea

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6
Q

Which medication inhibits dihydrofolate reductase?

A

Trimethoprim (in prokaryotes) and Methotrexate (in eukaryotes)

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7
Q

Which medication inhibits thymidylate synthase?

A

5-Fluorouracil

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8
Q

Which medication inhibits inosine monophosphate dehydrogenase?

A

Mycophenolate

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9
Q

Which medication inhibits PRPP amidotransferase?

A

6-Mercaptopurine

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10
Q

What accounts for the positive charge of histones?

A

Lysine + Arginine

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11
Q

What accounts for the negative charge of DNA?

A

Phosphate groups

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12
Q

How many adenine residues are found in a molecule of DNA if ONE strand contains A=2000, G=500, C=1500, and T=1000?

A

3,000 adenine residues

remember DNA is a double helix: one strand has 2000 and the complementary strand has 1000 which are paired to thymine

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13
Q

What strand of DNA nucleotides opposes this DNA strand: 5’-ATTGCGTA-3’?

A

5’-TACGCAAT-3’

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14
Q

How does UV radiation damage DNA?

A

makes pyrimidine dimers on same strand

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15
Q

Which eukaryotic DNA polymerase replicates the lagging strand?

A

DNA polymerase Alpha

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16
Q

Which eukaryotic DNA polymerase synthesizes RNA primers?

A

DNA polymerase Alpha

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17
Q

Which eukaryotic DNA polymerase repairs DNA?

A

DNA polymerase Beta

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18
Q

Which eukaryotic DNA polymerase replicates mitochondrial DNA?

A

DNA polymerase Gamma

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19
Q

Which eukaryotic DNA polymerase replicates the leading strand?

A

DNA polymerase Delta

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20
Q

Which structural motifs allow proteins to bind to DNA?

A

Helix-loop-helix

Helix-turn-helix

Zinc finger

Leucine zipper protein

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21
Q

What amino acid is encoded by the most common start codon?

A

Methionine (AUG)

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22
Q

What is the difference between an intron and an exon?

A

Intron => non-coding region, gets spliced out and stays in the nucleus

Exon => coding region, gets transcribed

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23
Q

Production of what enzyme is regulated by the lac operon?

A

Beta-galactosidase

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24
Q

What two proteins regulate the lac operon?

A

CAP (catabolite activating protein) and lac repressor

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25
Q

What two substrate conditions must be met for the lac genes to be transcribed?

A

Absent/no glucose, excess lactose

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26
Q

What enzyme matches amino acids to tRNA?

A

Aminoacyl-tRNA synthetase

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27
Q

What antibiotics are inhibitors of prokaryotic protein synthesis at the 30S ribosome?

A

Aminoglycosides (e.g. Gentamicin, Streptomycin, Neomycin)

Tetracyclines

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28
Q

What antibiotics are inhibitors of prokaryotic protein synthesis at the 50S ribosomal subunit?

A

Clindamycin

Chloramphenicol

Macrolides (e.g. Erythromycin, Azithromycin, Clarithromycin)

Linezolid

Streptogramins (e.g. Quinupristin/Dalfopristin)

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29
Q

What are the Hardy-Weinberg equations for population genetics?

A

p + q = 1

p^2 + 2pq + q^2 = 1

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30
Q

What mode of inheritance is often due mutations in one gene and due to defects in structural genes?

A

Autosomal dominant

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31
Q

What mode of inheritance is often due to enzyme deficiencies and is usually only seen in one generation?

A

Autosomal recessive

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32
Q

What mode of inheritance skips generations and has no male-to-male transmission?

A

X-linked recessive

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33
Q

What mode of inheritance results in transmission of disease from affected father to all daughters but no sons?

A

X-linked dominant

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34
Q

What mode of inheritance is transmitted only through the mother?

A

Mitochondrial inheritance

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35
Q

What is the differences between Southern blot, Northern blot, and Western blot?

A

Southern: DNA sample, DNA probe

Northern: RNA sample, DNA probe

Western: protein sample, Antibody probe

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36
Q

What type of test uses a known antigen to discern the presence of an antibody?

A

Indirect ELISA

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37
Q

What type of test is performed in order to diagnose chromosomal imbalances?

A

Karyotyping

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38
Q

What are the different eukaryotic RNA polymerases? What do they each make?

A

RNA polymerase I => makes rRNA (most numerous, synthesized in the nucleolus)

RNA polymerase II => makes mRNA (largest RNA, synthesized in the nucleoplasm)

RNA polymerase III => makes tRNA (tiny RNA, synthesized in the nucleoplasm)

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39
Q

What is the characteristic DNA sequence of the promoter region? What does a mutation in the sequence cause?

A

Promoter region: (-25)TATA box, (-75)CAAT box, (-10)Pribnow/TATAAT box

Mutation => decreased gene transcription

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40
Q

Which enzyme is responsible for tRNA charging?

A

Aminoacyl-tRNA Synthetase

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41
Q

Which enzyme catalyzes peptide bond formation?

A

Peptidyltransferase

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42
Q

What are the different prokaryotic RNA polymerases

A

only 1 prokaryotic RNA polymerase (multi-subunit complex)

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43
Q

What enzyme is deficient in Lesch-Nyhan Syndrome? What is the treatment?

A

Enzyme deficient => HGPRT

Tx: Allopurinol

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44
Q

What are the mRNA stop codons?

A

UAG, UAA, UGA

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45
Q

What are the differences between carbamoyl phosphate synthetase (CPS) I and CPS II?

A

CPS I: mitochondria, urea cycle, ammonia is nitrogen source

CPS II: cytosol, pyrimidine synthesis, glutamin is nitrogen source

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46
Q

A muscle biopsy on a patient of yours reveals elevated glycogen levels, elevated fructose-6-phosphate, and decreased pyruvate. What enzyme deficiency do you suspect most?

A

Phosphofructokinase-1

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47
Q

How does a low insulin/high glucagon state inhibit glycolysis and lead to conversion of energy?

A

Low insulin/high glucagon => more active protein kinase A => active FBP-2 => less fructose-2,6-bisP => less active PFK-1 => less glycolysis

High insulin/low glucagon => less active protein kinase A => active PFK-2 => more fructose-2,6-bisP => active PFK-1 => more glycolysis

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48
Q

What enzymes convert glucose to glucose-6-phosphate?

A

Hexokinase (most tissues)

Glucokinase (liver and beta-cells in pancreas)

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49
Q

What is the clinical consequence of a glycolytic enzyme deficiency?

A

Hemolytic anemia (no ATP in RBCs)

50
Q

What enzymes are responsible for increasing and decreasing the intracellular levels of fructose-2,6-bisphosphate?

A

Increasing => PFK-2 (more activation of PFK-1 => glycolysis)

Decreasing => FBP-2 (less activation of PFK-1 => gluconeogenesis)

51
Q

What is the rate-limiting enzyme in the glycolytic pathway?

A

PFK-1

52
Q

What is the formula for Gibbs free energy?

A

ΔG = ΔH - TΔS

53
Q

What irreversible enzymes are involved in gluconeogenesis?

A
  1. Pyruvate carboxylase (requires Biotin)
  2. PEP-CK
  3. Fructose-1,6-bisphosphatase (rate-limiting step)
  4. Glucose-6-phosphatase
54
Q

What enzyme catalyzes the rate-limiting step in gluconeogenesis?

A

fructose-1,6-bisphosphatase

55
Q

What is the rate-limiting enzyme for glycogen synthesis?

A

Glycogen synthase

56
Q

What is the rate-limiting enzyme for glycogenolysis?

A

Glycogen phosphorylase

57
Q

Which enzyme converts glucose-6-phosphate to glucose?

A

Glucose-6-phosphatase

58
Q

Which glycogen storage disease is characterized by a deficiency in glycogen phosphorylase?

A

McArdle disease (Type V)

59
Q

Which glycogen storage disease is characterized by a deficiency in glucose-6-phosphatase?

A

VonGierke Disease (Type I)

60
Q

Which glycogen storage disease is characterized by lactic acidosis, hyperlipidemia, and hyperuricemia (gout)?

A

VonGierke Disease (Type I)

61
Q

Which glycogen storage disease is characterized by a deficiency in alpha-1,6-glucosidase?

A

Cori disease (Type III)

alpha-1,6-glucosidase = debranching enzyme

62
Q

Which glycogen storage disease is characterized by a deficiency in alpha-1,4-glucosidase?

A

Pompe disease (Type II)

63
Q

Which glycogen storage disease is characterized by cardiomegaly?

A

Pompe disease (Type II) - Infant type

64
Q

Which glycogen storage disease is characterized by diaphragm weakness leading to respiratory failure?

A

Pompe disease (Type II) - Adult type

65
Q

Which glycogen storage disease is characterized by increased glycogen in the liver and severe fasting hypoglycemia?

A

VonGierke Disease (Type I)

66
Q

Which glycogen storage disease is characterized by hepatomegaly, hypoglycemia, and hyperlipidemia (with normal kidneys, lactate, and uric acid)?

A

Cori disease (Type III)

67
Q

Which glycogen storage disease is characterized by painful muscle cramps and myoglobinuria with strenuous exercise?

A

McArdle Disease (Type V)

68
Q

Which glycogen storage disease is characterized by severe hepatosplenomegaly and enlarged kidneys?

A

VonGierke Disease (Type I)

69
Q

What vitamin deficiency results from Hartnup disease?

A

Niacin (Vitamin B3)

70
Q

Why are alanine and glutamine found in such high concentrations in the blood?

A

they are the two major carriers of nitrogen from tissues

71
Q

What enzymes catalyze transamination reactions?

A

Aminotransferases/Transaminases

transfer amino group from an amino acid to alpha-ketoglutarate => forms glutamate

72
Q

What are the two most important transaminases? What reactions do they catalyze?

A

Alanine Transaminase (ALT): carries amino groups from the muscle to the liver (pyruvate + glutamate => alanine + alpha-KG)

Aspartate Transaminase (AST): 
(oxaloacetate + glutamate => aspartate + alpha-KG)
73
Q

What cofactor is required by all transaminases?

A

Pyridoxal phosphate (a derivative of vitamin B6)

74
Q

What are the four possible products of pyruvate?

A

Alanine (ALT)

Oxaloacetate

Lactate

Acetyl-CoA

75
Q

What are the two main nitrogen transporters in the blood?

A

Glutamine and alanine

76
Q

What are the major regulatory enzymes of the citric acid (TCA) cycle?

A

Citrate synthase

Isocitrate dehydrogenase (RLS)

alpha-Ketoglutarate dehydrogenase

77
Q

What substances are known to inhibit the complexes of the electron transport chain?

A

Complex I - Rotenone, Amytal, MPP

Complex III - Antimycin A

Complex IV - Cyanide, CO, H2S, Azide (N3-)

Complex V/ATPase - Oligomycin

78
Q

What substances can increase the permeability of the inner mitochondrial membrane, thereby decreasing ATP synthesis but increasing heat generation?

A

2,4-Dinitrophenol

Aspirin (high dose)

Thermogenin

79
Q

In patients with G6PD deficiency, ingestion of what substances can induce oxidative damage to RBCs?

A

“Spleen Purges Nasty Inclusions From Damaged Cells”

Sulfonamides

Primaquine

Nitrofurantoin

Isoniazid

Fava beans

Dapsone

Chloroquine

80
Q

What is the rate-limiting step of the pentose phosphate pathway?

A

Glucose-6-phosphate dehydrogenase (G6PD)

81
Q

Which tissues of the body use the pentose phosphate pathway?

A

RBCs, Liver, adrenal cortex, mammary glands (during lactation)

82
Q

How does a deficiency of the enzyme that is the rate limiter for the HMP shunt can result in hemolytic anemia?

A

RBCs are more susceptible to oxidative damage => RBC lysis => hemolytic anemia

83
Q

What are the symptoms of classic galactosemia?

A

FTT, intellectual disability, hepatomegaly, jaundice, infantile cataracts

84
Q

What disorder is caused by a deficiency in Galactokinase?

A

Galactokinase Deficiency

85
Q

What disorder is caused by a deficiency in Aldolase B?

A

Fructose Intolerance

86
Q

What disorder is caused by a deficiency in Lactase?

A

Lactose intolerance

87
Q

What disorder is caused by a deficiency in Galactose-1-phosphate uridyltransferase?

A

Classic Galactosemia

88
Q

What disorder is caused by a deficiency in Fructokinase?

A

Essential Fructosuria

89
Q

What fuels are produced and used in the post-absorptive period?

A

Produced: Glucose (from hepatic glycogenolysis/gluconeogenesis), Fatty Acids (from adipose tissue)

Used: muscles, brain, and other tissues use predominantly glucose

90
Q

When does gluconeogenesis begin in the post-absorptive period? When does it become fully active?

A

Begins 4-6 hours after the last meal

Fully active when glycogen stores are depleted (10-18 hours after last meal)

91
Q

How does the pattern of fuel production and usage change in early starvation (24 hours after the last meal)?

A

Produced: Glucose, Fatty acids

Used: Brain uses predominantly glucose. Muscles and other tissues use some glucose, but predominantly fatty acids.

92
Q

In intermediate starvation (48 hours after the last meal), how does the pattern of fuel production and utilization change?

A

Produced: Glucose, MORE fatty acids, Ketone Bodies

Used: Brain uses predominantly glucose, but also some ketone bodies. Muscles and other tissues use predominantly fatty acids, but also some ketone bodies.

93
Q

What metabolic scenario favors the synthesis of ketone bodies?

A

When production of acetyl-CoA from Beta-oxidation of fatty acids exceeds the oxidative capacity of the TCA cycle.

94
Q

True or False? Ketone bodies can be used by all body tissues including the brain.

A

FALSE - RBCs can only use glucose!

95
Q

What is the pattern of fuel production and utilization in prolonged starvation (5 days after last meal)?

A

Produced: Glucose, Fatty acids, Ketone bodies

Used: Brain uses predominantly ketone bodies. Muscles and other tissues use predominantly fatty acids, but also some ketone bodies.

96
Q

What is the primary energy source in a patient that has not eaten in two days?

A

Fatty acids

97
Q

What is the rate-limiting enzyme in ketone body synthesis?

A

HMG-CoA synthase

98
Q

A stressed physician comes home from work, consumes seven or eight shots of tequila in rapid succession before dinner, and becomes hypoglycemic. Why did she become hypoglycemic?

A

Ethanol metabolism => increased NADH => pyruvate and oxaloacetate => lactate and malate (respectively) => NO enzymes for gluconeogenesis!

99
Q

What are some of the hallmark features of kwashiorkor?

A

“FLAMES”

Fatty Liver

Anemia

Malnutrition (no proteins)

Edema

Skin lesions/hypopigmentation

100
Q

What deficiency causes familial hypercholesterolemia?

A

LDL receptors (lipoprotein lipase/Apo C-II)

101
Q

Which apolipoprotein activates LCAT?

A

Apo A-1

102
Q

Which apolipoprotein mediates chylomicron secretion?

A

Apo B-48

103
Q

Which apolipoprotein mediates VLDL secretion?

A

Apo B-100

104
Q

Which apolipoprotein is a cofactor for lipoprotein lipase?

A

Apo C-II

105
Q

Which apolipoprotein mediates the uptake of remnant particles?

A

Apo E

106
Q

What is the rate-limiting step for fatty acid synthesis?

A

Acetyl-CoA carboxylase

107
Q

What is the rate-limiting step for beta-oxidation of fatty acids?

A

Carnitine acyltransferase-1

108
Q

What is the rate-limiting step for ketone body synthesis?

A

HMG CoA synthase

109
Q

What is the rate-limiting step for cholesterol synthesis?

A

HMG CoA reductase

110
Q

What are the essential amino acids?

A

“PVT TIM HaLL”

PVT: Phenylalanine, Valine, Threonine

TIM: Tryptophan, Isoleucine, Methionine

HaLL: Histidine, Leucine, Lysine

111
Q

What is the amino acid precursor to Histamine?

A

Histidine

112
Q

What is the amino acid precursor to Porphyrin and heme?

A

Glycine

113
Q

What is the amino acid precursor to Nitric Oxide?

A

Arginine

114
Q

What is the amino acid precursor to GABA?

A

Glutamate

115
Q

What is the amino acid precursor to SAM (s-adenosyl-methionine)?

A

Methionine

116
Q

What is the amino acid precursor to Creatinine?

A

Arginine

117
Q

A full-term neonate feeds poorly, is hyperactive and has a musty odor. What is the diagnosis?

A

PKU

decreased/deficient phenylalanine hydroxylase

118
Q

A patient with PKU should have a diet low in phenylalanine. What other dietary modifications should a patient with PKU make?

A

Increase tyrosine and tetrahydrobiopterin in the diet

119
Q

A middle-aged man has dark spots on his sclera and has noted that his urine turns black when left sitting for a period of time. What is the diagnosis?

A

Alkaptonuria

120
Q

What is the underlying cause of maple syrup urine disease?

A

decreased branched-chain alpha-ketoacid dehydrogenase complex

USMLE Buzzwords - WLB (9 decks)

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