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Step 1 (Steffanie) > Biochem > Flashcards

Biochem Flashcards

1
Q

What is the deficiency in Niemann-Pickett Disease? What accumulates?

A

Sphingomyelinase deficiency. Sphingomylein accumulates.

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2
Q

What are the clinical features of Niemann-Pickett Disease?

A

Hepatosplenomegaly, neurologic regression, cherry-red macular spot in infancy

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3
Q

What causes HbC disease?

A

Missense mutation that results in glutamate residue being substituted by lysine in both beta globin chains

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4
Q

List the speeds of hemoglobin movement for hemoglobin A, S, and C in electrophoresis

A

Hemoglobin A > S > C

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5
Q

What causes sickle cell disease?

A

Missense mutation that result in nonpolar valine replacing a negatively charged glutamate in both beta globin chains

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6
Q

List the steps of the polyol pathway

A
  1. aldolase reductase coverts glucose into sorbitol

2. sorbitol slowly metabolized into fructose by sorbitol dehydrogenase

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7
Q

Which prokaryotic DNA polymerases have 3’ to 5’ exonuclease activity?

A

DNA polymerase I, II, and III

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8
Q

Which prokaryotic DNA polymerase has 5’ to 3’ exonuclease activity and can remove RNA primers?

A

DNA polymerase I

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9
Q

What do organophosphates do to acetylcholine?

A

Inhibit its breakdown, leading to state of cholinergic excess

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10
Q

How does 2,3-BPG effect hemoglobin’s affinity for oxygen? Consequences of this effect?

A

It allosterically decreases hemoglobin’s affinity for oxygen. In the presence of low oxygen, higher 2,3-BPG enables increased oxygen delivery to the tissues

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11
Q

What causes the rubber like properties of elastin?

A

Extensive cross-linking between elastin monomers, which is facilitated by lysyl oxidase

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12
Q

What forms abnormally in patients with Ehlers-Danlos Syndrome?

A

Collagen

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13
Q

How does Ehlers-Danlos Syndrome manifest?

A

Hypermobile joints, hyperelastic skin, and fragile tissue susceptible to bruising, wounding, and hemarthrosis

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14
Q

What causes Marfan syndrome?

A

Inherited defect in fibrillin-1, an extracellular glycoprotein that acts as a scaffold for elastin

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15
Q

Which enzyme is deficient in classic galactosemia?

A

Galactose-1-phosphate uridyl transferase

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16
Q

What are the symptoms of classic galactosemia?

A

Vomiting, lethargy, jaundice, E.coli sepsis

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17
Q

What is the treatment for classic galactosemia?

A

Cessation of breastfeeding and switching to soy based formula

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18
Q

Fibrates inhibit which enzyme?

A

Cholesterol 7alpha-hydroxylase. Can lead to cholesterol stones

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19
Q

What is deficient in hereditary fructose intolerance? What accumulates?

A

Aldolase-B is deficient. Toxic metabolite fructose-1-phosphate accumulates

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20
Q

What clinical effects are seen in hereditary fructose intolerance?

A

Hypoglycemia and vomiting when fructose or sucrose is consumed

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21
Q

Describe the Haldane effect

A

In the lungs, the binding of oxygen to hemoglobin drives the release of H+ and CO2 from hemoglobin

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22
Q

Describe the Bohr effect

A

In the peripheral tissues, high concentrations of CO2 and H+ facilitate oxygen unloading from hemoglobin

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23
Q

What causes porphyria cutanea tarda (PCT)?

A

Uroporphyrinogen decarboxylase deficiency

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24
Q

How does porphyria cutanea tara present?

A

Photosensitivity, which manifests as vesicle and blister formation on sun exposed areas as well as edema, erythema, pruritus, and pain

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25
Q

Which cofactor is used for carboxylase enzymes?

A

Biotin (Vitamin B7)

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26
Q

Ingestion of what has been associated with a biotin deficiency?

A

Excess ingestion of avidin, found in raw egg whites

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27
Q

What are the clinical features of a biotin deficiency?

A

Mental status changes, myalgias, anorexia, macular dermatitis, and lactic acidosis

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28
Q

What process does acidosis stimulate in the kidneys?

A

Renal ammoniagenesis, a process by which renal tubular epithelial cells metabolize glutamine to glutamate, generating ammonium

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29
Q

What is defective in maple syrup urine disease?

A

Breakdown of branched chain amino acids

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30
Q

Which co-enzymes are required by branched chain alpha-ketoacid dehydrogenase complex?

A

Thiamine, Lipoate, Coenzyme A, FAD, NAD

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31
Q

What are the clinical features of Maple Syrup Urine Disease?

A

Neurotoxicity that includes seizures, irritability, lethargy, and poor feeding. Sweet odor to urine (from metabolite of isoleucine)

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32
Q

How is Maple Syrup Urine Disease treated?

A

Some patients improve with high dose thiamine treatment but most require lifelong restriction of leucine, isoleucine, and valine

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33
Q

Which enzymes are inhibited by lead?

A

Ferrochelatase and ALA Dehydratase

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34
Q

What stimulates glycogenolysis in skeletal muscle?

A

Increased intracellular calcium

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35
Q

What causes homocystinuria?

A

Defect in cystathionine synthase

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36
Q

Which amino acid is essential in patients with homocystinuria?

A

Cysteine

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37
Q

Which inherited hyperlipoproteinemia is characterized by xanthomas and premature coronary and peripheral vascular disease

A

Familial dysbetalipoproteinemia

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38
Q

Describe the defect in familial dysbetalipoproteinemia

A

Defects in ApoE3 and ApoE4 lead to decreased clearance of chylomicrons and VLDL remnants causing elevated triglyceride and cholesterol levels

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39
Q

Which enzyme is deficient in propionic acidemia?

A

Propionyl-CoA Carboxylase

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40
Q

How does propionic acidemia present?

A

Lethargy, poor feeding, vomiting, and hypotonia 1-2 weeks after birth

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41
Q

Which enzyme is deficient in Fabry disease?

A

Alpha-galactosidase A

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42
Q

What accumulates in Fabry disease?

A

Globotriaosylceramide (Gb3)

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43
Q

Symptoms of Fabry disease?

A

Neuropathic pain, hypohidrosis, angiokeratomas, telangiectasias, cerebrovascular and cardiac diseases, renal failure

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44
Q

What makes up the transmembrane domain of a G protein-coupled receptor?

A

Nonpolar, hydrophobic amino acids (alanine, valine, leucine, isoleucine, phenylalanine, tryptophan methionine, proline, glycine)

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45
Q

What is the function of the amino acids that make up the transmembrane domain of a G protein coupled receptor?

A

Anchor the transmembrane region of the protein to the hydrophobic core of the phospholipid bilayer

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46
Q

What is a common cause of brown pigmented gallstones in East Asian countries?

A

The liver fluke sinensis

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47
Q

What are brown pigmented gallstones made up of?

A

Calcium salts and unconjugated bilirubin

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48
Q

What enzyme plays an important role in pathogenesis of brown pigment gallstones?

A

Beta-glucoronidase

49
Q

What do proteins destined for the lysosome require?

A

Phosphorylation of specific mannose residues to ensure proper transit through the golgi apparatus

50
Q

What enzyme catalyzes the phosphorylation of mannose residues on lysosome bound proteins?

A

Golgi body phosphotransferase enzyme

51
Q

What are the symptoms of inclusion cell disease?

A

Failure to thrive, cognitive deficits in the first year of life, and characteristic facial features such as coarse facial features and corneal clouding

52
Q

What cofactor is required for transaminase enzymes?

A

Pyridoxine (Vit B6)

53
Q

What disorders are characterized by impaired ability to oxidize VLCFAs?

A

Peroxisomal disorders

54
Q

How does Zellweger syndrome present?

A

Presents in early infancy with craniofacial abnormalities (widened sutures, large anterior fontanelle), hepatomegaly, and profound neurologic defects (hypotonia, seizures, developmental delay). Death usually occurs withing months of inital presentation

55
Q

Why do maturing erythrocytes lose their ability to synthesize heme?

A

They lose their mitochondria, which are necessary for heme synthesis

56
Q

What is the enzyme deficiency in PKU?

A

Phenylalanine hydroxylase or its cofactor tetrahydrobiopterin

57
Q

How does PKU present?

A

Severe intellectual disability and seizures if left untreated. Hypopigmentation of the skin, hair, eyes, and catecholaminergic brain nuclei

58
Q

What accumulates in PKU?

A

Phenylalanine accumulates in body fluids and the CNS

59
Q

What causes methylmalonic acidemia?

A

Autosomal recessive complete or partial deficiency of the enzyme methylmalonyl-CoA mutase

60
Q

How does methylmalonic acidemia present?

A

Lethargy, vomiting, and tachypnea in a newborn. Labs show metabolic acidosis, ketotic hypoglycemia, and hyperammonemia. Elevated urine methylmalonic acid and propionic acid

61
Q

Which substance directly stimulates the first enzyme involved in gluconeogenesis?

A

Acetyl-CoA

62
Q

What are the hallmark effects of phenylketonuria?

A

Intellectual disability, serotonin deficiency, and hyperphenylalanemia

63
Q

Which enzyme is deficient in acute intermittent porphyris?

A

Porphobilinogen deaminase

64
Q

What are the findings with acute intermittent porphyria?

A

Abdominal pain, neurological manifestations, and port wine colored urine. PBG & ALA in urine. No photosensitivity

65
Q

How are acute intermittent porphyria attacks managed?

A

Glucose or hemin inhibits ALA synthase activity

66
Q

What is used to treat cyanide poisoning?

A

Nitrites because they can induce methemoglobinemia (Fe3+ instead of Fe2+)

67
Q

Why does pyruvate kinase deficiency result in splenomegaly?

A

Pyruvate kinase deficiency causes hemolytic anemia. Splenic hyperplasia results from increased work of the splenic parenchyma, which remove the deformed erythrocytes from circulation

68
Q

What causes pellegra? What are the symptoms?

A

Deficiency of niacin (Vit B3). Dermatitis, diarrhea, and dementia

69
Q

Niacin is synthesized endogenously from which what precursor?

A

Tryptophan

70
Q

What is the most abundant amino acid in collagen?

A

Glycine. Occupies every 3rd amino acid position in the alpha chain

71
Q

What are the symptoms of riboflavin (Vit B2) deficiency?

A

Angular stomatitis, cheilitis, glossitis, seborrheic dermatitis, keratitis, corneal neovascularization, and anemia

72
Q

Who typically presents with riboflavin deficiency?

A

Chronic alcoholics and the severely malnourished

73
Q

What are the symptoms of Vitamin C deficiency?

A

Capillary bleeding, poor wound healing, periodontal disease. Bony deformities and subperiosteal hemorrhages in children.

74
Q

What is Vitamin C required for?

A

Hydroxylation of proline and lysine resides in pro-collagen

75
Q

What causes alkaptonuria?

A

Autosomal recessive disorder of tyrosine metabolism leading to accumulation of homogentistic acid

76
Q

What are clinical features of alkaptonuria?

A

Black urine color when exposed to air, a blue-black pigment to the face, and ochronotic arthropathy

77
Q

What amino acid is esswntial in PKU?

A

Tyrosine

78
Q

What are the clinical features of PKU?

A

Intellectual disability, seizures, light pigmentation, and a “musty” odor

79
Q

Nutritional restriction of which of the following substances can improve ornithine translocase deficiency?

A

Protein restriction improves the condition by reducing the amount of amino acid turnover

80
Q

How does Pompe disease present?

A

Presents in early infancy with cardiomegaly, macroglossia, and profound muscular hypotonia

81
Q

What enzyme deficiency causes Pompe disease?

A

Acid maltase (acid alpha-glucosidase)

82
Q

What is seen on muscle biopsy in Pompe disease?

A

Glycogen accumulation within lysosomal vesicles

83
Q

What can cause hyperhomocysteinemia?

A

MTHFR deficiency or deficiencies of B vitamins cobalamin, pyridoxine, and folate

84
Q

Name the antioxidant enzymes

A

Superoxide dismutase, glutathione peroxidase, catalase

85
Q

Describe pellagra

A

Photosensitive dermatitis, diarrhea, and dementia occurring secondary to vitamin B3 (Niacin) deficiency

86
Q

What is Niacin a precursor for? Where are these used as cofactors?

A

Precursor for NAD and NADP which are important co-enzymes for many dehydrogenase and reductase enzymes

87
Q

Which enzyme converts pyruvate to acetyl coenzyme A?

A

Pyruvate dehydrogenase

88
Q

Which motor protein mediates anterograde axonal transport?

A

Kinesin

89
Q

What conditions promote sickling in sickle cell anemia?

A

Low oxygen levels, increased acidity, or low blood volume

90
Q

Which disorders are associated with a mutation in JAK2 and activation of STAT proteins?

A

Chronic myeloproliferative disorders (Polycythemia vera, essential thrombocytosis, primary myelofibrosis)

91
Q

Which amino acids can provide energy without increasing lactate production?

A

Exclusively ketogenic amino acids - lysine and leucine

92
Q

How do patients with essential fructosuria metabolize fructose?

A

Some is converted by hexokinase to fructose-6-phosphate, which can enter glycolysis

93
Q

Which hormone contributes to glucose homeostasis during prolonged fasting and has receptors found within the cytoplasm?

A

Cortisol

94
Q

What deficiency can cause Ehlers-Danlos syndrome?

A

Procollagen peptidase deficiency, which results in impaired cleavage of terminal propeptides in the extracellular space

95
Q

Which pathway does glucose-6-phosphate dehydrogenase participate in?

A

Rate-limiting enzyme in pentose phosphate pathway, the major source of cellular NAPDH. NADPH is necessary for reducing glutathione and for biosynthesis of cholesterol, fatty acids, and steroids

96
Q

What causes the greenish color to develop in bruises?

A

Heme oxygenase converts heme to biliverdin

97
Q

If subunits of hemoglobin are separated, what does their oxygen-dissociation curve look like?

A

Hyperbolic, similar to that of myoglobin

98
Q

How can thiamine deficiency be diagnosed?

A

If baseline erythrocyte transketolase activity is low but increased after addition of thiamine pyrophosphate

99
Q

What step in the citric acid cycle synthesis GTP?

A

Synthesized by succinyl-CoA synthetase during conversion of succinyl-CoA to succinate in the citric acid cycle

100
Q

What are the clinical manifestations of homocystinuria?

A

Ectopic lentis, intellectual disability, marfanoid habitus. Pts are at high risk for thromboembolic occlusion, especially in brain, heart, and kidneys

101
Q

Cause of homocystinuria

A

Autosomal recessive deficiency of cystathionine beta-synthase, an enzyme requiring pyridoxine (B6) as a cofactor.

102
Q

How is homocystinuria treated?

A

~50% of affected patients respond to high doses of pyridoxine. Additional treatment includes dietary restriction of methionine

103
Q

During catabolism of proteins, where are amino acid groups transferred?

A

To alpha-ketoglutarate

104
Q

Increased levels of which substance inhibits beta oxidation of fatty acids?

A

Malonyl-CoA

105
Q

What does ethanol inhibit?

A

Gluconeogenesis - can cause hypoglycemia once hepatic glycogen stores are depleted

106
Q

Intellectual disability, gait or posture abnormality, eczema, musty body odor

A

Phenylketonuria (PKU)

107
Q

PKU mutation

A

The gene that codes for phenylalanine hydroxylase

108
Q

Deficiency in maple syrup urine disease?

A

Branched chain alpha-ketoacid dehydrogenase complex

109
Q

How is maple syrup urine disease diagnosis confirmed?

A

Presence of elevated branched-chain amino acid levels

110
Q

Therapy for maple syrup urine disease

A

Dietary restriction of branched chain amino acids - leucine, isoleucine, valine

111
Q

Describe the PI3K/Akt/mTOR pathway

A

Intracellular signaling pathway important for anti-apoptosis, cellular proliferation, and angiogenesis. Mutations that enhance this pathway contribute to cancer pathogenesis

112
Q

What sequence on tRNA is used as a recognition sequence by proteins?

A

CCA

113
Q

Thiamine deficiency

A

Vit B1. Deficiency causes beriberi and Wernicke-Korsakoff syndrome.

114
Q

What causes essential fructosuria?

A

Fructokinase deficiency

115
Q

How is some of the fructose load converted in pts with essential fructosuria?

A

By hexokinase to fructose-6-phosphate

116
Q

Elevated levels of methylmalonic acid and homocysteine

A

Vit B12 deficiency

117
Q

Ras is only active when bound by which substance?

A

GTP

118
Q

Which enzyme is usually deficient with impaired beta oxidation of fatty acids?

A

Acyl-CoA dehydrogenase

Step 1 (Steffanie) (21 decks)

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