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SUM: Medical Biochemistry > Q bank II > Flashcards

Q bank II Flashcards

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USMLE® Step 1 flashcards
1
Q

Which of the following tissues or organs plays a significant role in gluconeogenesis after 4 days of fasting but not after and overnight fasting?

A

Kidney. If its for overnight, then its the liver

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2
Q

All of the following tissues can use circulating fatty acids as metabolic fuel except:

A

Brain

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3
Q

Analysis of a patient’s serum showed elevated VLDL. Which of the following mechanisms accounts in part for this process?

A

decreased activity of lipoprotein lipase

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4
Q

The isozyme form of creatine kinase in skeletal muscle is

A

MM

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5
Q

Which one of the following glucose transporters are regulated by insulin?

A

GLUT 4

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6
Q

Most sphingolipidoses results from genetic deficiencies of which one of the following enzymes

A

glycosidases

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7
Q

The conversion of Propionyl-Coa to succinyl-Coa requires

A

biotin and vitamin B12

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8
Q

The release of arachidonate by phospholipase A2 from membrane phospholipids is inhibited by

A

lipocortin

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9
Q

The two nitrogen atoms in urea arise from

A

ammonia and aspartic acid

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10
Q

The normal brown red color of feces results from the presence of

A

Stercobilin

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11
Q

The most common drug-induced hemolytic anemia is found in patients who are deficient in which of the following enzymes

A

Glucose-6-phosphate dehydrogenase

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12
Q

Patients with a antiproteinase deficiency may develop emphysema because they cannot.

A

block the action of leukocyte elastase released by activated neutrophils in the lung

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13
Q

Marfan syndrome is associated with a defect in the structure of

A

Elastin

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14
Q

All of the cells are stimulated by epinephrine except

A

Glucose Oxidation

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15
Q

The inhibition of the DNA synthesis by methotrexate results from direct inhibition of

A

The reduction of dihydrofolate to tetrahydrofolate

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16
Q

A liver biopsy from an infant with a large liver and kidney, hypoglycemia acidosis and hyperlipidemia revealed a massive buildup of glycogen with a normal structure. A possible diagnosis would be.

A

Glucose-6-phosphatase deficiency (von Gierke’s disease)

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17
Q

Which of the following compounds are the most ketogenic?

A

amino acids that are degraded to Acetyl-CoA

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18
Q

McArdle disease is a myopathy that results in an ability to perform anaerobic exercise. the disease is due to a deficiency of the enzyme that catalyzes the predominant reaction of glycogenolysis and this enzyme involves which one of the following processes?

A

phosphorolysis reaction

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19
Q

The extracellular 1st messenger that initiates the cAMP dependent glycogenolytic cascade in muscle is

A

Epinephrine

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20
Q

Increased formation of ketone bodies during starvation is due to

A

increased levels of free fatty acids in serum

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21
Q

A lack of insulin in humans would result in which one of the following reactions in the liver?

A

increased formation of 3-hydroxybutyrate

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22
Q

Sulfa drugs interfere with the bacterial synthesis of

A

Folic Acid

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23
Q

What is true statement about Niemann-Pick disease

A

it is due to a deficiency of the enzyme that hydrolytically removes phosphorylcholine from spingomyelin

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24
Q

The primary biochemical lesion in patients with familial hypercholesterolemia is:

A

The functional deficiency of plasma membrane receptors for low-density lipoproteins

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25
Q

Which one of the following is correct regarding the well fed state?

A

The major source of fuel for the brain is glucose

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26
Q

All of the following vitamins give rise to cofactors that are phosphorylated in the active form exept

A

riboflavin

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27
Q

Most major metabolic pathways are considered to be either mainly anabolic or catabolic. Which of the following pathways is most correctly considered to be amphibolic?

A

Citric Acid Cycle

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28
Q

Insulin regulates fatty acid synthesis by

A

dephosphorylating of acetyl-Coa carboxylase

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29
Q

Respiratory distress syndrome in premature infants is due to inadequate secretion of which one of the following lipids?

A

phosphatidylcholine

30
Q

A cyclooxygenase is required for the production of

A

thromboxanes from arachidonic acid

31
Q

The symptom of the dietary deficiency of of niacin (which results in pellagra) will be less severe if the diet has a high content of

A

Tryptophan

32
Q

Each of the following vitamins is required for the reactions in the oxidation of pyruvate to CO2 and H2O EXCEPT:

A

Biotin

33
Q

The major process responsible for maintaining blood glucose 4 hours after the last meal is:

A

glycogenolysis

34
Q

The major process responsible for maintaining blood glucose 40 hours after the last meal is

A

gluconeogenesis

35
Q

In an individual at rest who has fasted for 12 hours:

A

phosphorylase, pyruvate kinase and glycogen synthetase are phosphorylated in liver

36
Q

Administration of a high dose of glycogen to this patient 2-3 hours after a high carbohydrate meal:

A

would have little effect on blood glucose level

37
Q

. Which one of the following sequences places the lipoprotein in the order of most dense to least dense?

A

HDL/ LDL/VLDL/chylomicron

38
Q

Which one of the following occurs in the conversion of fatty acids to ketone bodies?

A

Acetoacetate and acetyl CoA are produced y cleavage of HMG CoA*

39
Q

Pyridoxial phosphate is required for the enzymes catalyzing the reaction

A

pyruvate + glutamate –> alanine + alpha ketoglutarate

40
Q

In the human, prostaglandin can be derived from:

A

.arachidonic acid

41
Q

Which of the following metabolites is the stoichiometric substrate of the Kreb Cycle?

A

Acetyl CoA

42
Q

Malic enzyme performs all the following functions EXCEPT

A

catalyzing the gernation of malate from pyruvate

43
Q

Pyruvate dehydrogenase phosphatase deficiency in humans has which of the following effects:

A

it leads to lactic acidemia*

44
Q

. Which of the following is a true statement regarding cytosolic carbamoyl-phosphate synthetase II in humans?

A

it is one of the 3 activities residing in a single polypeptide called CAD complex*

45
Q

5-Phosphoribosyl 1 pyrophosphate (PRPP) is an intermediate in all the following pathways EXCEPT:

A

the pentose phosphate pathway

46
Q

Thymidylate synthase, an enzyme whose activity is high in rapidly dividing tumor cells, performs all the following function EXCEPT:

A

providing pyrimidine nucleotides for mRNA synthesis

47
Q

The mechanism of action of glucagon involves all of the following steps EXCEPT

A

activation protein kinase C

48
Q

the enzyme in the heme biosynthetic pathway that is most sensitive to lead is

A

Aminolevulinic acid (ALA) dehydratase

49
Q

The rate limiting reaction in protoporphyrin IX synthesis is catalyzed by

A

Aminolevulinic acid (ALA) synthase

50
Q

The first step in heme catabolism

A

heme oxygenase

51
Q

The rate limiting step in urea cycle is

A

carbamoyl phosphate synthetase I

52
Q

Which one of the following amino acids is catabolized preferentially by the liver when compared with skeletal muscle?

A

alanine

53
Q

The elevated blood glucose seen in diabetes melliatus is a consequence of:
failure of glucose to enter liver cells

A

increased activity of gluconeogenic enzymes due to enzyme induction by glucagon

54
Q

Which one of the following enzymes is rate limiting for de novo purine nucleotide synthesis and is thus a target for drugs used in treatment in gout?

A

phosphoribosylpyrophosphate-glutamine amidotransferase (PRPP amidotransferase

55
Q

The elevation of blood ketone bodies results from deficiency of the enzyme:

A

Succinyl CoA-acetoacetate CoA-transferase

56
Q

What is the first purine nucleotide formed during de novo synthesis

A

inosine monophosphate

57
Q

The administration of L-dopa which is given in the treatment of Parkinson’s disease bypass the rate limiting enzyme of catecholamine biosynthesis. What is the name of the enzyme?

A

tyrosine hydroxylase

58
Q

Dermatan and heparan sulfates accumulate in Hurler’s syndrome

A

alpha-L iduronidase

3’phosphoadenosine 5’ phosphosulfate (PAPS)

59
Q

Which of the following is true concerning transketolase?

A

It utilizes TPP as cofactor in catalyzing the transfer of two carbon fragment from one sugar phosphate to another

60
Q

Dinitrophenol uncouples oxidation and phosphorylation in which one of the following ways?

A

By dissipating the proton gradient between the mito matrix and the intermembrane space

61
Q

Aspirin is an irreversible inhibitor of:

A

cyclooxygenase

62
Q

All of the following are true statements regarding glutamine PRPP amidotransferase EXCEPT

A

it is activated by IMP

63
Q

Which AA binds to zinc of zinc finger proteins?

A

cysteine and histidine

64
Q

Which of the following compounds is not an allosteric regulator of PFK activity?

A

F6P

65
Q

A deficiency of any of the following AA leads to negative nitrogen balance in humans EXCEPT

A

ornithine

66
Q

The rate limiting reaction in prostaglandin biosynthesis:

A

phospholipase A2

67
Q

Which enzyme requires TPP as a cofactor in pentose phosphate pathway?

A

transketolase

68
Q

The enzyme that catalyzes an anaplerotic reaction in the citric acid cycle is:

A

pyruvate carboxylase

69
Q

Which one of the following statement about the major collagen type from skin or bone is correct

A

The procollagen molecule contains non helical C- and N- terminal extensions

70
Q

The congenital deficiency of a1-antitrypsin is associated with susceptibility of

A

emphysema

71
Q

Chronic or long term regulation of enzymatic activity as opposed to acute changes in enzymatic activity ,is best affected by which of the following regulatory controls?

A

synthesis or degradation of enzyme

SUM: Medical Biochemistry (26 decks)

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