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Step 1 DIT > 12. Biochem > Flashcards

12. Biochem Flashcards

1
Q

What is the rate-limiting enzyme in purine synthesis? In pyrimidine synthesis?

A

purine: glutamine PRPP amidotransferase
pyrimidine: CPS2 (carbamoyl phosphate synthetase 2)

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2
Q

What are the sources of carbon in the synthesis of purines? (3) in pyrimidine synthesis? (2)

A
  • purines: CO2, glycine, tetrahydrofolate

- pyrimidines: aspartate, CO2

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3
Q

Which medication inhibits each of the following enzymes?

- ribonucleotide reductase

A

hydroxyurea

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4
Q

Which medication inhibits each of the following enzymes? (2)

- dihydrofolate reductase

A

TMP, methotrexate

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5
Q

Which medication inhibits each of the following enzymes?

- thymidylate synthase

A

5-FU

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6
Q

Which medication inhibits each of the following enzymes?

- inosine monophosphate (IMP) dehydrogenase

A

mycophenolate

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7
Q

Which medication inhibits each of the following enzymes?

- PRPP amidotransferase

A

6-MP

- note this is the rate-limiting enzyme

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8
Q

What accounts for the positive charge of histones? What accounts for the negative charge of DNA?

A

histones: b/c made of lysine and arginine

DNA: negative b/c of phosphate groups

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9
Q

How does UV radiation damage DNA?

A

makes pyrimidine dimers (usually T-T) on the same strand of DNA –> makes “bulky” helix-distorting lesion

need repair via nucleotide excision repair

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10
Q

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

A

AUG –> methionine

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11
Q

What is the diff. b/w an intron and exon?

A

Intron: non-coding segment of DNA
Exon: coding sequences for specific protein products

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12
Q

Production of what enzyme is regulated by the lac operon?

A

b-galactosidase

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13
Q

What two proteins regulate the lac operon?

A
  • CAP

- lac repressor

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14
Q

What 2 substrate conditions must be met for the lac genes to be transcribed?

A
  • abundant lactose (removes repressor)

- low glucose (allows CAP to bind)

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15
Q

What enzyme matches amino acids to tRNA?

A

aminoacyl tRNA synthetase

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16
Q

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

A
  • aminoglycoside

- tetracyclines

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17
Q

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

A
  • chloramphenicol
  • clindamycin
  • macrolides
  • linezolid
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18
Q

What enzymes convert glucose to glucose-6-phosphate?

A

hexokinase or glucokinase (only in liver and b-cells of pancreas)

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19
Q

What is the clinical consequence of a glycolytic enzyme deficiency?

A

hemolytic anemia

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20
Q

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

A

PFK-2 (fed): increase level of fructose 2,6-BP

FBPase-2 (fasting): decrease level of fructose 2,6-BP

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21
Q

What is the rate limiting enzyme in the glycolytic pathway?

A

phosphofructokinase-1

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22
Q

What irreversible enzymes are involved in gluconeogenesis (4)

A
  1. pyruvate carboxylase (with biotin)
  2. PEP carboxylase
  3. fructose-1,6-bisphosphatase
  4. glucose-6-phosphatase
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23
Q

What enzyme catalyzes the rate-limiting step in gluconeogenesis?

A

fructose-1,6-bisphosphatase

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24
Q

What is the rate limiting enzyme for glycogen synthesis? For glycogenolysis?

A
  • glycogen synthase

- glycogen phosphorylase

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25
Q

Which enzyme converts G-6-P to glucose?

A

glucose-6-phosphatase

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26
Q

Which glycogen storage disease matches each of the following phrases?
- glycogen phosphorylase deficiency

A

McArdle

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27
Q

Which glycogen storage disease matches each of the following phrases?
- glucose-6-phosphatase

A

Von Gierke

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28
Q

Which glycogen storage disease matches each of the following phrases?
- lactic acidosis, hyperlipidemia, hyperuricemia (gout)

A

Von Gierke

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29
Q

Which glycogen storage disease matches each of the following phrases?
- a-1,6-glucosidase deficiency

A

cori

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30
Q

Which glycogen storage disease matches each of the following phrases?
- a-1,4-glucosidase deficiency

A

Pompe

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31
Q

Which glycogen storage disease matches each of the following phrases?
- cardiomegaly

A

pompe (infantile type)

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32
Q

Which glycogen storage disease matches each of the following phrases?
- diaphragm weakness leading to resp failure

A

pompe (adult type)

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33
Q

Which glycogen storage disease matches each of the following phrases?
- increased glycogen in liver, severe fasting hypoglycemia

A

Von Gierke

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34
Q

Which glycogen storage disease matches each of the following phrases?
- hepatomegaly, hypoglycemia, hyperlipidemia (normal kidneys, lactate, uric acid)

A

cori

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35
Q

Which glycogen storage disease matches each of the following phrases?
- painful muscle cramps, myoglobinuria with strenous exercise

A

McArdle

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36
Q

Which glycogen storage disease matches each of the following phrases?
- severe hepatosplenomegaly, enlarged kidneys

A

von gierke

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37
Q

What are the possible products of pyruvate? (4)

A
  • acetyl-coa
  • oxaloacetate
  • lactate
  • alanine
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38
Q

What are the two main nitrogen transporters in the blood?

A
  • alanine

- glutamine

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39
Q

What are the major regulatory enzymes of the TCA cycle? (3)

A
  • citrate synthase
  • isocitrate dehydrogenase
  • a-ketoglutarate dehydrogenase
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40
Q

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

A
  • amytal
  • rotenone
  • MPP
  • antimycin A
  • cyanide (CN)
  • azide (N3-)
  • carbon monoxide (CO)
  • hydrogen sulfide (H2S)
41
Q

What substances can increase the permeability of the inner mitochondrial membrane, thereby decreasing ATP synthesis but increasing heat generation? (3)

A

uncoupling agents

  • aspirin (high dose)
  • thermogenin (in brown fat)
  • 2,4-dinitrophenol
42
Q

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

A

G6PD

43
Q

Which tissues of the body use the pentose phosphate pathway? (4)

A
  • RBCs
  • liver
  • adrenal cortex
  • mammary glands
44
Q

Explain why a deficiency of the enzyme that is the rate limiter for the HMP shunt can result in hemolytic anemia

A

G6PD deficiency

  • decreased NADPH –> decreased reduced glutathione
  • RBCs more susceptible to oxidative damage –> hemolysis
45
Q

What are the symptoms of classic galactosemia?

A
  • failure to thrive
  • intellectual disability
  • hepatomegaly
  • jaundice
  • infantile cataracts
46
Q

What disorder is caused by a deficiency of each of the following enzymes?
- galactokinase

A

galactokinase deficiency

47
Q

What disorder is caused by a deficiency of each of the following enzymes?
- aldolase B

A

fructose intolerance

48
Q

What disorder is caused by a deficiency of each of the following enzymes?
- lactase

A

lactose intolerance

49
Q

What disorder is caused by a deficiency of each of the following enzymes?
- galactose-1-phosphate uridyltransferase

A

classic galactosemia

50
Q

What disorder is caused by a deficiency of each of the following enzymes?
- fructokinase

A

essential fructosuria

51
Q

What is the primary energy source in a patient that has not eaten in 2 days?

A

fatty acids

52
Q

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

A

HMG-CoA synthase

53
Q

How does ethanol leads to hypoglycemia?

A
  • increase NADH when you metabolize ethanol
  • shunts pyruvate towards production of lactate, and oxaloacetate –> malate
  • thus, pyruvate and oxaloacetate no longer available for gluconeogenesis
54
Q

What are some of the hallmark features of kwashiorkor?

A

FLAMES

  • fatty liver
  • anemia
  • malnutrition
  • edema
  • skin lesions
55
Q

What deficiency causes familial hypercholesterolemia?

A

deficiency in LDL receptor

56
Q

which apolipoprotein matches each of the following statements?
- activates LCAT

A

ApoA-1

57
Q

which apolipoprotein matches each of the following statements?
- mediates chylomicron secretion

A

ApoB-48

58
Q

which apolipoprotein matches each of the following statements?
- mediates VLDL secretion

A

ApoB-100

59
Q

which apolipoprotein matches each of the following statements?
- cofactor for lipoprotein lipase

A

ApoC-II

60
Q

which apolipoprotein matches each of the following statements?
- mediates uptake of remnant particles

A

ApoE

61
Q

What is the rate-limiting enzyme for fatty acid synthesis

A

acetyl CoA carboxylase

62
Q

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

A

carnitine acyl transferase 1

63
Q

What is the rate-limiting enzyme for ketone body synthesis

A

HMG CoA synthase

64
Q

What is the rate-limiting enzyme for cholesterol synthesis

A

HMG CoA reductase

65
Q

What are the essential amino acids?

A

Private (PVT) TIM HaLL

  • phenylalanine
  • valine
  • threonine
  • tryptophan
  • isoleucine
  • methionine
  • histidine
  • leucine
  • lysine
66
Q

What amino acid is the precursor to the following?

- histamine

A

histidine

67
Q

What amino acid is the precursor to the following?

- porphyrin, heme

A

glycine

68
Q

What amino acid is the precursor to the following?

- NO

A

arginine

69
Q

What amino acid is the precursor to the following?

- GABA

A

glutamate

70
Q

What amino acid is the precursor to the following?

- S-adenosyl-methionine (SAM)

A

methionine

71
Q

What amino acid is the precursor to the following?

- creatinine

A

arginine

72
Q

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

A

PKU

- deficiency in phenylalanine hydroxylase or BH4

73
Q

A patient with PKU should have a diet low in phenylalanine. What other dietary modification should a pt with PKU make? (2)

A
  • high tyrosine diet

- BH4 supplementation

74
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

- defect with homogentisate oxidase

75
Q

What is the underlying cause of maple syrup urine disease?

A

deficiency of branched chain a-ketoacid dehydrogenase complex

76
Q

What has been the most common clinical scenario of excess iron ingestion in the last 3 decades?

A

infant consuming iron-fortified vitamins (prenatal vitamins)

77
Q

What are some of the clinical effects of zinc deficiency?

A
  • delayed wound healing
  • impaired immune response
  • rash around eyes, mouth, nose, anus (acrodermatitis enteropathica)
78
Q

What are some of the signs of hypocalcemia?

A
  • tetany and neuromuscular irritability
  • Chvostek sign
  • Trousseau sign
79
Q

What organs are primarily affected by excess of mercury?

A

kidney and brain

80
Q

What vitamin in excess can cause hypercalcemia?

A

vitamin D

81
Q

What are the symptoms of vitamin A toxicity

A
  • visual impairment
  • fatigue
  • ataxia
  • headache
  • increased ICP (pseudotumor cerebri)
  • alopecia
82
Q

What clinical features would lead you to suspect that a patient has scurvy?

A
  • sore spongy gums
  • loose teeth
  • hemorrhage (b/c fragile vessels)
  • swollen joints (hemarthrosis)
  • impaired wound healing
83
Q

Vitamin C is necessary for the hydroxylation of which amino acids in collagen synthesis? (2)

A
  • proline

- lysine

84
Q

Which enzymes are used to convert cholecalciferol to calcitriol?

A
  1. 25-hydroxylase (liver)

2. 1a-hydroxylase (kidney)

85
Q

A patient presents with convulsions and irritability. What vitamin deficiency is causing these symptoms in this patient?

A

B6 (remember, B6 required for synthesis of GABA)

86
Q

What type of anemia can be caused by folate or B12 deficiency?

A

megaloblastic anemia

87
Q

Where is B12 absorbed into the circulation?

A

Terminal ileum

88
Q

Which vitamin deficiency matches?

- peripheral neuropathy, glossitis

A

B12, B6

89
Q

Which vitamin deficiency matches?

- neural tube defects

A

B9 (folate)

90
Q

Which vitamin deficiency matches?

- dermatitis, diarrhea, dementia

A

B3 (niacin)

91
Q

Which vitamin deficiency matches?

- megaloblastic anemia

A

B9 (folate), B12

92
Q

Which vitamin deficiency matches?

- Pernicious anemia

A

B12

93
Q

Which vitamin matches each of the following?

- used in oxidation/reduction reactions

A

B2 (FAD)

B3 (NAD, NADP)

94
Q

Which vitamin matches each of the following?

- used in carboxylation reactions

A

Biotin (B7)

note: also vit K for gamma-carboxylation of glutamic acid

95
Q

Which vitamin matches each of the following?

- used by pyruvate dehydrogenase and a-ketoglutarate dehydrogenase

A

B1 (thiamine)

96
Q

Which vitamin matches each of the following?

- can be used to elevated HDL and lower LDL

A

B3 (niacin)

97
Q

Which vitamin matches each of the following?

- deficiency can be caused by isoniazid use

A

B6

98
Q

Which vitamin matches each of the following?

- cobalt is found within this vitamin

A

B12 (cobalamin)

99
Q

Which vitamin matches each of the following?

- critical for DNA synthesis

A

B9 (folate), B12

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