step 1 biochemistry

7/23/2019 Step 1 Biochemistry

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NBME STEP 1

METABOLISM

1. In the biosynthesis of glucose from pyruvate by the liver, the first intermediate formed from pyruvate isA) acetyl CoAB) alanineC) lactateD) methylmalonyl CoAE) oaloacetate

METABOLISMO: AMINO ACIDS

!. Amino acids that contribute "ith at least one nitrogen or carbon to the purine ring during thebiosynthesis of purine nucleotides are

A) Alanine, asparagine, and lysineB) Alanine, #ethionine, and $istidine

C) aspartate, arginine, and histidineD) aspartate, glycine, and glutamineE) glycine, serine, and tyrosine

GENETICS%) &igure.

In the pedigree illustrating a syndrome associated "ith various neoplasms, individuals "hose symbols aresolid blac' have manifestations of the syndrome. (he neoplasms and their ages at onset in the affectedindividuals are as follo"s

Pedigree number Type of neopl!m Age " on!e" #yer!$

I*! carcinoma of breast +right) !

carcinoma of breast +left) %-

II*! carcinoma of breast 1

II*% myofibrosarcoma /

III*! medulloblastoma

III*/ rhabdomyosarcoma

(his pedigree illustratesA) anticipationB) genetic heterogeneityC) incomplete penetranceD) multifactorial inheritanceE) variable epressivity


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MOLEC BIOL/. Eu'aryotic proteins that eist as a nonmembrane*associated, glycosylated, disulfide*lin'ed dimer inthe mature form are generally found in "hich of the follo"ing0

A) CytoplasmB) Etracellular spaceC) #itochondrial matriD) uclear matri

E) uclear pore

METABOLISM. 2hich of the follo"ing en3ymes acting on phosphatidylcholine "ill directly generate diacylglycerol0

A) $ormone*sensitive lipaseB) 4ipoprotein lipaseC) 5ancreatic lipaseD) 5hospholipase CE) 6phingomyelinase

METABOLISM

-. A %*"ee'*old infant has mil' intolerance due to a defect in the en3ymes that digest lactose. (hisen3yme is located at "hich of the follo"ing sites in enterocytes0

A) At the apical surfaces

B) At the basolateral surfaces

C) 2ithin the 7olgi comple

D) 2ithin lysosomes

E) 2ithin peroisomes

METABOLISM

8. 2hich of the follo"ing metabolic processes shares the same metabolic path"ay as that of thereaction sho"n0

A) Deamination of D*amphetamineB) &ormation of minoidil sulfateC) $ydrolysis of acetylsalicylic acidD) *Deal'ylation of desipramineE) *$ydroylation of meperidine

GENETICS


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. A child born "ithout limbs is found to have a mutation in a receptor for a fibroblast gro"th factor.(he absence of limbs most li'ely resulted from a disruption of the processes controlling "hich of thefollo"ing0

A) ApoptosisB) DifferentiationC) Epithelial*mesenchymal conversionsD) 5roliferation

GENETICS

9. A /*year*old boy is diagnosed by biochemical testing as having medium*chain acyl*CoAdehydrogenase +#CAD) deficiency, an autosomal recessive disorder of fatty acid oidation. A polymerasechain reaction +5C:) amplification of the region of the gene containing the common mutation is done. 5C:of both the mutant and normal genes yields an 8*base pair +bp) product. After coI digestion, ho"ever, themutant 5C: product yields -1* and !-*bp fragments, "hile the normal gene product is not cleaved. :esultsof this test on a DA sample from the boy and his family are sho"n. ;n the basis of this assay, "hich ofthe follo"ing conclusions about sibling % is most li'ely0

A) (he #CAD status of this sibling is indeterminate

B) (his sibling does not have #CAD deficiency

C) (his sibling has #CAD deficiency

D) (his sibling must have been the product of nonpaternity

MOLEC BIOL1


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1!. (he ma?ority of cellular proteins and :A are synthesi3ed throughout the cell cycle and are onlyinterrupted briefly during # phase. 6ynthesis of "hich of the follo"ing proteins occurs predominantly in 6phase of the cell cycle0

A) CyclinsB) DasesC) $istonesD) :A polymerasesE) sn:5s +small nuclear ribonucleoproteins)

&) (ubulins

1%& An in're!e in "(e '"i)i"y of *(i'( of "(e follo*ing en+yme! i! mo!" li,elyto increase the rateof metabolism of glucose -*phosphate through glycolysis in the liver0

A) &ructose 1,-*bisphosphatase

B) &ructose 1,-*bisphosphate aldolase +aldolase A)

C) &ructose !,-*bisphosphatase

D) 7luco'inase

E) -*5hosphofructo*1*'inase

1-& During DNA repli'"ion. *(i'( '"i)i"y 'on"ribu"e! "o "(e fideli"y #''ur'y$ of "(e DNApolymer!e/

A) DA ligase

B) Endonuclease

C) %@@ Eonuclease

D) @%@ Eonuclease

E) $elicase

1. 2hen a cytogenetic abnormality is suspected in an infant "ith multiple congenital anomalies,chromosomes from circulating leu'ocytes are analy3ed. (hese chromosomes are most condensed andeasiest to evaluate in "hich of the follo"ing states0

A) Anaphase

B) InterphaseC) #etaphaseD) 5rophaseE) (elophase


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10& A (yper'"i)e 0yerold girl de)elop! mi'ro'y"i' nemi. 'erebrl edem. and ataia.Determination of "hich of the follo"ing serum en3yme activities is most li'ely to confirm the diagnosis0

A) *Aminolevulinic acid +*A4A) dehydrogenase

B) 7lucose -*phosphate dehydrogenase

C) 7lutathione transferase

D) 4actate dehydrogenase

E) 5yruvate 'inase

12& 3(" i! "(e m4or 'on!e5uen'e of (eredi"ry defe'" in "(e produ'"ion ofactive pyruvate'inase in the liver and in erythrocytes0

A) Decreased capacity to fi C;!

B) Decreased gluconeogenesis from alanine

C) Decreased oidation of pyruvate

D) Decreased production of A(5 from glucose

E) Increased affinity of hemoglobin for oygen

1. A genetic element is found to contain several genes and to cataly3e its o"n movement "ithin andbet"een chromosomes. Inverted %*nucleotide repeats are present at the ends of this genetic element.(his genetic element in hepatocytes is incapable of replicating independently. Based on this description,this genetic element is best categori3ed as "hich of the follo"ing0

A) Comple transposonB) Insertion seuenceC) 5lasmidD) :egulon

16& BIOC7EM 89NS 7


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IMMNO!


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;;& In gou". (yperuri'emi re!ul"ing from o)erprodu'"ion of ur"e i! mo!" li,ely "o re!ul" from lac' of feedbac' inhibition by AD5 or 7D5 at "hich en3yme0

A) Adenosine deaminase

B) Dihydrofolate reductase

C) 7lucose -*phosphate dehydrogenase

D) ucleotide phosphorylase

E) 5hosphoribosylpyrophosphate synthetase

;%& A (el"(y %


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!-. Double*stranded DA can be denatured by heating and renatured by cooling. :enaturation underconditions of high stringency has "hich of the follo"ing effects0

A) Considerable base mismatching is permitted

B) 7C base pairing is inhibited

C) 7( base pairing is promoted

D) #ismatched DA hybridi3ation is prevented

!8. In mucolipidosis II +I*cell disease), the en3yme cataly3ing formation of mannose -*phosphate, thesignal for transfer to lysosomes, is missing. 5roteins destined for the lysosome are most li'ely to be found in"hich of the follo"ing locations in patients "ith this disease0

A) Endoplasmic reticulumB) Etracellular spaceC) 7olgi comple

D) #itochondriaE) ucleus

!.

A %*year*old boy is suspected of having an 9lin,ed immunodefi'ien'y. (o establish the pattern oftransmission of this genetic defect, DA is etracted from the ( and B lymphocytes of his parents, his t"osisters ages and 8 years, and his %*month*old brother. After restriction en3yme digestion, the digestedDA is sub?ected to gel electrophoresis and probed "ith a DA mar'er that distinguishes the maternal andpaternal H chromosome alleles. (he results are sho"n. Based on this DA analysis, "hich of the follo"ingstatements is correct concerning the inheritance of this genetic deficiency0

A) (he brother has inherited the defective geneB) Both parents can transmit the defective geneC) 6ister 1 is a carrierD) 6ister ! is a carrierE) Both sisters are carriers&) either sister is a carrier


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!9 A 18*year*old boy "ith moderate mental retardation has macro*orchidism. Cytogenetic analysissho"s a fragile site on the long arm of chromosome H. 2hich molecular defect is most li'ely associated"ith this abnormality0

A ) C77 repeat epansionB ) Eon deletionC ) 7ene amplificationD ) 5oint mutation

E ) 6plice site mutation

%


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%%. &ructose !,-*bisphosphate regulates "hich step in the diagram0

A)B)C)D)

E)&)7)$)I )R)

%/. (he ability of endothelial cells to inhibit platelet aggregation is mediated in part by the metabolism ofcell membrane*derived arachidonic acid by "hich of the follo"ing0

A) Anaerobic glycolysis

B) Cyclooygenase path"ay

C) 7lutathione reductase path"ay

D) 4ysosomal en3ymes path"ay

E) #ied function oidase path"ay

&) (ricarboylic acid path"ay

AA(;#J

%. (he genotype of the cells of the chorionic villi that comprise the human placenta is

A ) fetalB ) maternalC ) maternal and fetalD ) paternal


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%-. A 1


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step 1 biochemistry

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