USMLE 23

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rere_girl4ever
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297239
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USMLE 23
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2015-03-04 18:04:46
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USMLA 23
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USMLE 23
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  1. Tetrahydrobiopterin (BH4) is used as a cofactor in the synsthesis of?
    • Tyrosine
    • Dihydroxyphenylalanine
    • Serotonin
    • Nitric oxide
  2. 5-hydroxytryptamine is also known as?
    Serotonin
  3. Another name for serotonin is?
    5-hydroxytryptamine
  4. Where is serotonin synthesized from? What are the necessary cofactors?
    • Serotonin is synthesized from Tryptophan.
    • Cofactors: B6 and Tetrahydrobiopterin
  5. What are the causes of Phenylketonuria?
    • 1. Deficiency of phenylalanine hydroxylase
    • 2. Lack  of Tetrahydrobiopterin (due to dihydrobioptein reductase deficiency)
  6. How is G-aminobutyrate synthesized?
    • Glutamate is converted to G-aminobutyrate (GABA) by Glutamate decarboxylase.
    • B6 is used as a cofactor.
  7. What is the function of Glutamate decarboxylase?
    Converts Glutamate to GABA (G-aminobutyrate)
  8. Vitamin B12 is needed in the conversion of?
    • 1. Homocysteine to Methionine (by homocysteine methyltransferase)
    • 2. Methylmalonyl CoA to Succinyl-CoA (by methylmalonyl-CoA mutase/ ISOMERASE)
  9. What is pantothenic acid?
    B5
  10. What is the active form of pantothenic acid?
    Coenzyme A
  11. Pantothenic acid is an essential cofactor in which reactions?
    • In acetylation recations.
    • Oxaloacetate ⇨ Citrate by Acetyl-CoA
    • α-ketoglutarate ⇨ Succinyl-coA by α-ketoglutarate dehydrogenase
  12. This structure produces ribosomal RNA.
    • Nucleolus
  13. What is the function of the nucleolus?
    Site of ribosomal RNA synthesis
  14. In this pathology, vesicles and blisters form on sun exposed areas. What is the deficient enzyme? What is the accumulated substrate?
    • Deficient enzyme: Uroporphyrinogen decarboxylase
    • Accumulated substrate: Uroporphyrin (tea colored urine)
  15. Deficiency of Uroporphyrin decarboxylase results in?
    Porphyria cutanea tarda
  16. What is the function of Uroporphyrinogen decarboxylase?
    Converts Uroporphyrinogen III to Coproporphyrinogen III
  17. What is the function of δ-aminolevullinic acid synthase?
    • Converts Glycine + Succinyl-CoA to δ-aminolevulinic acid
    • B6 is a cofactor
  18. A deficiency of δ-aminolevulinic acid synthase results in?
    • Sideroblastic anemia
    • Microcytic hypochromic
  19. What is the most abundant amino acid in the collagen molecule?
    • Glycine
    • It occurs in at least every third amino acid postition.
  20. What is the amino acid formula of collagen?
    (Gly-X-Y-)333
  21. What are the amino acids designated X and Y in the amino acid sequence of collagen (Gly-X-Y)333?
    Many of the amino acids designated X and Y are PROLINE residues.
  22. What amino acid is essential in the formation of the alpha helix?
    Proline
  23. What is Type II glycogen storage disease?
    Pompe disease
  24. What enzyme is deficient in Pompe disease?
    Lysosomal α-1,4 glucosidase (acid maltase)
  25. A deficiency of lysosomal α-1,4 glucosidase is characteristic of?
    • Pompe disease
    • Acid maltase
  26. A deficiency of acid maltase is characteristic of?
    Pompe disease
  27. In this glycogen storage disease, polysacchardides (glycogen) accumulates within lysosomes.
    Pompe disease
  28. Describe the clinical presentation of Pompe disease.
    • Hepatomegaly
    • CARDIOMEGALY
    • Macroglossia
    • Hypotonia
    • Mental retardation
  29. Describe the lab/ microscopic findings in Pompe disease
    • Normal blood sugar levels
    • Polysaccharide/ glycogen accumulation in lysosomes
    • NORMAL glycogen structure
  30. Which cells cannot use ketone bodies and why?
    • Erythrocytes- lack a mitochondria
    • Hepatocytes-  lack the enzyme succinyl CoA-acetoacetate CoA transferase (thiophorase) which is required to convert acetoacetate to acetoacetyl CoA
  31. Which cells use ketone bodies for energy?
    • 1. Skeletal muscles
    • 2. Cardiac muscles
    • 3. Renal cortex
    • 4. Brain (during starvation)
  32. The 3' hydroxyl group necessary for the initiation of DNA synthesis is provided by which enzyme?
    Primase- provides 3' hydroxyl group
  33. What is the function of phenylalanine hydroxylase?
    Converts phenylalanine to tyrosine
  34. What is the function of tyrosinase?
    Converts tyrosine to melanin
  35. What is the major amino acid resposible for transferring ammonia to the liver for disposal?
    Alanine
  36. How is ammonia disposed?
    • 1. Alanine transports ammonia (NH3) to the liver
    • 2. In the liver, alanine is transaminated by alanine aminotransferase to pyruvate
    • 3. The NH3 is transferred to α- KETOGLUTARATE  to form GLUTAMATE
    • 4. Glutamate is further metabolized by the enzyme glutamate dehydrogenase, which liberates free ammonia and regenerates α-ketoglutarate.
    • 5. Ammonia then enters the urea cycle to form urea, which is subsequently excreted in the urine.
  37. What is the use of enteropeptidase?
    Converts trypsinogen to trypsin
  38. This enzyme is essential for the conversion of trypsinogen to trypsin
    Enteropeptidase/ Enterokinase
  39. This condition causes lipase deficiency.
    • Chronic pancreatitis
    • This leads to poor fat absorption and steatorrhea (foul smelling bulky stools containing undigested fat)
  40. What are the chronic toxicities of Vitamin A overuse?
    • Alopecia
    • Dry skin- SCALINESS 
    • Hepatic toxicity/ hepatomegaly
    • PSEUDOTUMOR CEREBRI- Papilledema- swelling of optic disc due to ⇧intracranial pressue.
  41. Pseudotumor cerebri is associated with which vitamin use?
    Vitamin A overuse
  42. What are the cofactors required by Pyruvate dehydrogenase in the conversion of Pyruvate to acetyl CoA?
    • 1. B1: Thiamine pyrophosphate
    • 2. B2 (Riboflavin): FAD
    • 3. B3 (Niacin): NAD
    • 4. B5 (pantothenic acid): CoA
    • 5. LIPOIC ACID
    • NOTE: α-ketoglutarate complex requires the same as the pyruvate dehydrogenase complex.
  43. Vomiting, rice-water stools and garlic breath are diagnostic of?
    Arsenic poisoning- inhibits lipoic acid
  44. This substance inhibits lipoic acid. What are the manifestations?
    • Arsenic poisoning
    • Findings: Vomiting, rice-water stools, garlic breath
  45. What are the cofactors required by the α-ketoglutarate dehydrogenase complex?
    • 1. B1: Thiamine pyrophosphate
    • 2. B2 (Riboflavin): FAD
    • 3. B3 (Niacin): NAD
    • 4. B5 (pantothenic acid): CoA
    • 5. LIPOIC ACID
    • NOTE: The pyruvate dehydrogenase complex  requires the same cofactors as the α-ketoglutarat dehydrogenase complex.
  46. What causes methylmalonic acidemia /aciduria?
    Results from a defect in the ISOMERIZATION reaction that transforms methylmalonyl CoA to Succinyl CoA by methylmalonyl-CoA mutase (isomerase).
  47. This enyme converts methylmalonyl-CoA to Succinyl-CoA.
    Methylmalonyl-CoA mutase a.k.a ISOMERASE
  48. What is the function of the enzyme isomerase?
    • Converts methylmalonyl-CoA to Succinyl-CoA.
    • A.k.a Methylmalonyl-CoA mutase
  49. Where is Uracil found?
    RNA
  50. Which enzyme involved in DNA synthesis catalyzes the formation of RNA strands?
    Primase
  51. Which cells are rich in smooth endoplasmic reticulum?
    • Steroid producing cells.
    • Liver hepatocytes
    • Adrenals
    • Gonads
  52. What is the function of the COP II coated transport vesicles?
    Transports proteins from the RER to the Golgi apparatus.
  53. Describe the structure of a transmembrane domain.
    • Spans the membrane
    • Composed of alpha helices with approximately 20 hydrophobic amino acid residues such as valine, alanine, isoleucine, methionine and phenylalanine.
  54. These drugs inhibit formation of the initiation complex,
    • Aminoglycosides
    • Gentamycin
    • Neomycin
    • Amikacin
    • Tobramycin
    • Streptomycin
  55. This drug interferes with the binding of aminoacyl-tRNA to the A site.
    Tetracycline, Doxycycline, Minocycline
  56. What is the MOA of Doxycycline?
    Bind to 30s ribosome and prevents the binding of aminoacyl-tRNA to the A site. 
  57. What is the MOA of Minocycline?
    Bind to the 30s ribosome and prevents the binding of aminoacyl-tRNA to the A site.
  58. What is the MOA of Tetracycline?
    Binds to the 30s ribosome and prevents the binding of aminoacyl-tRNA to the A site.
  59. Describe the MAP kinase pathway.
    • 1. Insulin/ Growth factors bind to tyrosine kinase causing autophosphorylation of the receptor.
    • 2. Phosphorylated tyrosine kinase reacts with SH2 domain proteins and SOS protein leading to RAS activation.
    • 3. Active form of RAS is bound to GTP.
    • 4. Ras activtes Raf kinase.
    • 5. Raf kinase activates MAP kinase.
    • 6. Activated MAP kinase enters the nucleus to influence gene transcription.
  60. Lipoic acid is a cofactor for which mitochondiral enzymes?
    • Pyruvate dehydrogenase
    • α-ketoglutarate dehydrogenase
    • Branched chain ketoacid dehydrogenase
  61. Describe the DNA of the mitochondia.
    Small, circular chromosomes
  62. This cellular organelle codes for proteins, tRNA and rRNA.
    Mitochondria
  63. Label the heterochromatin and euchromatin.
    • Euchromatin- less condensed, transcriptionally active
    • Heterochromatin- condensed, transcriptionally inactive
  64. Describe the metabolism of Arginine.
    • Arginine is metabolized to Urea and Ornithine.
    • H2O is given off in this process.
  65. Describe the presentation of Wet beri beri.
    • High output congestive heart failure and neurological symptoms
    • (dilated cardiomyopathy)
  66. Anti-snRNP antibodies are present in which disease?
    Mixed connective tissue disease
  67. Which autoantibodies are present in mixed connective tissue disease?
    • Anti-snRNP 
    • Anti-U1 RNP
  68. Anti-U1 RNP autoantibodies are present in which disease?
    Mixed connective tissue disease
  69. What is the pathology seen below?
    Centriacinar emphysema
  70. Label the diagram below.
    • 1. Pulmonary artery (right side)
    • 2. Lung (right side) 
    • 3. Superior vena cava. 
    • 4. Ascending thoracic aorta.
    • 5, Pulmonary trunk.
    • 6, Pulmonary vein (left side). 
    • 7, Pulmonary artery (left side).
    • 8, Scapula. 
    • 9, Rib 
    • 10, Lung (left side).
  71. Test A is newly available for diagnosing myocardial infarction. In  a recent study, the results of test A (compared to a gold standard diagnosis of MI were as follows:
     
    The patient has a positive result on test A. Assuming his pre-test probability is equivalent to the prevalence of MI in the study, what is the probability that the patient has an MI?
    • The PPV of a diagnostic test answers this question: Given a positive test result, what is the probability that the patient has the disease?
    • PPV= 200/ 200+50
  72. Label the diagram of the heart below.
    • a- left ventricle
    • b- right ventricle
    • c- right atrum
    • d- left atrium
  73. What is the function of the Nef gene in HIV infection?
    Nef decreases expression of MHC class I proteins on the surfaces of infected cells.
  74. In HIV infection, this viral gene decreases expression of MHC class I proteins on the surfaces of infected cells.
    Nef
  75. What is the function of the Tat gene in HIV infection?
    Tat plays a role in viral replication.
  76. What is normal PaCO2?
    33-45mmHg
  77. What is normal bicarbonate?
    22-28 mEq/L
  78. Describe the acid/base physiology of Salicylate / Aspirin intoxication.
    • 1. Respiratory alkalosis- due to stimulation of medullary respiratory center ⇛ HYPERVENTILATION
    • 2. Metabolic acidosis- due to accumulation of organic acids due to inhibition of TCA ect.
  79. Secretion from this sweat gland can become malodorous secondary to bacterial decomposition on the skin surface.
    Apocrine

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