MCB 250 Exam 2 Questions and Answers Updated 2026

MCB 250 Exam 2 Questions and
Answers Updated 2026
ForBaBcovalentlyBclosedBcircularBdouble-strandedBDNA,BtheBlinkingBnumberBis:



A.BequalBtoBtheBnumberBofBhelicalBturnsBinBtheBDNABdoubleBhelix.

B.BtheBnumberBofBhydrogenBbondsBholdingBtheBtwoBstrandsBtogether.

C.BanBinvariantBtopologicalBpropertyBofBthatBDNABmolecule.

D.BalteredBbyBdistortingBtheBshapeBofBtheBDNABmolecule.B-
BAnswerC.BanBinvariantBtopologicalBpropertyBofBthatBDNABmolecule.



InBNature,BDNABsupercoilingBisBalmostBalwaysBnegative.BWhy?

A.BNegativeBsupercoilingBkeepsBDNABfromBdenaturingBatBhighBtemperatures.

B.BNegativeBsupercoilingBrelaxesBcircularBDNAs.

C.BNegativeBsupercoilingBcompactsBDNA.

D.BNegativeBsupercoilingBisBanBinherentBpropertyBofBright-'handedBhelices.

E.BNegativeBsupercoilingBstoresBenergyBforBcellularBprocessesBthatBrequireBstrandBseparation.B
-
BAnswerE.BNegativeBsupercoilingBstoresBenergyBforBcellularBprocessesBthatBrequireBstrandBsep
aration.



TypeBIBtopoisomerasesBareBcapableBofBdoingBallBofBtheBfollowingBexcept:

A.BModifyBDNABtopologyBwithoutBusingBATP.

B.BIncreaseBtheBnegativeBsupercoilingBofBDNA.

C.BAlterBtheBlinkingBnumberBofBaBDNABmoleculeBinBstepsBofB1.

D.BRelaxBtheBfreeBenergyBstoredBinBsupercoiling.

E.BCleaveBandBresealBphosphodiesterBbondsBinBtheBDNABbackbone.B-
BAnswerB.BIncreaseBtheBnegativeBsupercoilingBofBDNA.



WhichBofBtheBfollowingBreactionsBwithBcovalentlyBclosed,BcircularBDNAB(cccDNA)BdoesBNOTBr
esultBinBaBnewBlinkingBnumber?

A.BincubationBwithBethidiumBbromide

B.BincubationBwithBaBtypeBIIBtopoisomerase

, C.BaBbriefBincubationBwithBDNaseBfollowedBbyBresealingBtheBbreaksBinBtheBphosphodiesterBb
ackboneBwithBanotherBenzymeB(DNABligase)

D.BincubationBwithBaBtypeBIBtopoisomeraseB-BAnswerA.BincubationBwithBethidiumBbromide



GyraseBisBdifferentBfromBotherBTypeBIIBtopoisomerasesBbecauseBGyrase:

A.BcanBrelaxBpositivelyBsupercoiledBDNA.

B.BdoesBnotBrequireBATP.

C.BcanBintroduceBnegativeBsupercoilsBintoBnegativelyBsupercoiledBDNA.

D.BhasBanBactiveBsiteBphenylalanineBinsteadBofBtyrosine.B-
BAnswerC.BcanBintroduceBnegativeBsupercoilsBintoBnegativelyBsupercoiledBDNA.



HistonesBformBhydrogenBbondsBwithBwhatBpartBofBtheBDNA?

A.BwithBtheBphosphodiesterBbackboneBandBwithBbasesBviaBtheBminorBgroove

B.BonlyBwithBbasesBviaBtheBmajorBgroove

C.BonlyBwithBbasesBviaBtheBminorBgroove

D.BwithBtheBphosphodiesterBbackboneBandBwithBbasesBviaBtheBmajorBgrooveB-
BAnswerA.BwithBtheBphosphodiesterBbackboneBandBwithBbasesBviaBtheBminorBgroove



TheB10BnmBfiberBandBtheB30BnmBfiberBareBtwoBchromatinBstructuresBthatBdifferBinBwidth.B
WhichBcomparisonBbetweenBtheseBtwoBstructuresBisBINCORRECT?

A.BDNABisBmoreBheavilyBcompactedBinBtheB30BnmBfiber.

B.BFormationBofBtheB30BnmBfibersBrequiresBhistoneBproteinBH1.

C.BDNABisBmoreBaccessibleBtoBtheBenzymesBthatBregulateBitsBfunctionBinBtheB30BnmBfiber.

D.BInBtheB30BnmBfiber,BmoreBDNABisBassociatedBwithBnucleosomesBandBtheBlinkerBDNABisBs
horter.

E.BFormationBofBtheB30BnmBfiberBrequiresBmodificationsBofBtheBtailBdomainsBofBtheBcoreBhis
tones.B-
BAnswerC.BDNABisBmoreBaccessibleBtoBtheBenzymesBthatBregulateBitsBfunctionBinBtheB30Bnm
Bfiber.



WhatBisBtheBroleBofBDNABhelicase?

A.BRelaxBpositiveBDNABsupercoils

B.BBindBsingleBstrandedBDNABandBkeepBitBfromBreanealling

C.BConferBprocessivityBtoBDNABPolBIII