Chapter 16 Study Guide answers PDF

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This is the study guide answers for chapter 16 in Berndtson's class...

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Answers'to'Chapter'16'Study'Questions' ! 1.!What!two!different!types!of!organisms!did!Griffith!use!to!conduct!his!studies?!!Griffith!used!two!strains!of! the!bacterium,!Streptococcus*pneumonia*(S-pathogenic!and!R-nonpathogenic)*and!mice.!!Use!the! following!table!to!help!outline!his!experiment.! ! ! Bacteria!used! Experiment! Result! Control!1! Living!S-strain! Injected!into!mice! Mice!died!of!pneumonia! Control!2! Living!R!strain! Injected!into!mice! Mice!remained!healthy! Control!3!! Heat!killed!S-strain! Injected!into!mice! Mice!remained!healthy! Experiment! Mixture!of!heat!killed!SInjected!mixture! Mice!died!of!pneumonia! strain!and!living!R!cells! into!mice! Living!bacteria!in!mice!blood!were! “transformed”!into!the!S!strain! Why!was!the!S-strain!pathogenic?!!This!strain!produced!a!capsule!that!protected!the!bacteria!from!the! host’s!(mouse)!immune!system.!!What!was!Griffith’s!conclusion?!!An!unknown!heritable!substance!from! dead!S!cells!allowed!R!cells!to!make!capsules!and!thus!transformed!the!R!cells!into!S!cells.!!Did!Griffith! know!what!the!unknown!heritable!substance!was?!!No! ! 2.!!!What!was!the!overall!purpose!of!the!experiment!conducted!by!Hershey!and!Chase!with!radiolabelled!T2! bacteriophage!and!E.*coli?!!The!purpose!of!this!experiment!was!to!try!to!discern!if!the!hereditary! material!was!DNA!or!protein.!!! What!happens!to!E.*coli!when!it!is!infected!with!T2!bacteriophage?!!T2!reprograms!the!bacterial!cell!to! make!thousands!of!virus!particles.!!! What!does!a!T2!phage!look!like?!!T2!phage!is!a!simple!virus!consisting!of!a!protein!coat!that!incudes!the! phage!head,!tail!sheath,!and!tail!fibers.!!The!DNA!is!found!in!the!head!of!the!virus.!!! Why!was!35S!used!to!label!T2!proteins?!The!amino!acid!methionine!and!cysteine!contain!sulfur.!!Nucleic! acids!do!not!contain!sulfur.!!! Why!was!32P!used!to!label!DNA?!!Phosphate!is!found!in!the!backbone!of!a!DNA!strand.!!Phosphorous!in! not!found!in!amino!acids.!!! When!the!labeled!T2!phage!infected!E.*coli!cells,!where!was!radioactivity!found!after!the!cultures!were! agitated!and!centrifuged!to!pellet!bacterial!cells?!!Use*the*table*below*to*answer*this*question.! ! Location!of!radioactivity!after!agitation! Conclusion:! and!centrifugation!of!bacterial!cells! 35 S-labeled!proteins!! Supernatant! The!viral!proteins!did!not!enter!the! bacterial!cells.!!Proteins!must!not!be! the!hereditary!material! 32 P-labeled!DNA! Pellet!!! The!viral!DNA!entered!the!bacterial! Newly!synthesize!phage!particles!also! cells!and!directed!the!synthesis!of! contained!DNA!that!was!partially!labeled! new!viral!particles.! with!32P.! DNA!must!be!the!hereditary!material! in!T2!bacteriophage! ! 3.!!Why!did!scientists!initially!believe!that!proteins!were!the!carrier!of!genetic!information?!!Compared! to!nucleic!acids,!proteins!are!more!complex!and!heterogeneous!molecules.!!! Cite!evidence!generated!from!Erwin!Chargaff!that!revealed!that!DNA!has!molecular!diversity!among! species.!!The!content!of!adenine!was!30%!in!humans!but!26%!in!E.!coli.!!! What!is!Chargaff’s!rule?!!Within!a!species,!the!number!of!adenines!=!number!of!thymines,!and!the! number!of!guanines!=!number!of!cytosines.!

4.!!Several!scientists!were!working!simultaneously!on!the!3-D!structure!of!DNA.!!Who!were!these! scientists?!!Linus!Pauling:!!California!Institute!of!Technology;!Maurice!Wilkins!and!Rosalind!Franklin:!! Kings!College!in!London;!and!James!Watson!and!Francis!Crick:!!Cambridge!University.!!! Which!one!of!these!scientists!generated!the!critical!X-ray!diffraction!data!that!provided!evidence!that! DNA!formed!a!double!helix?!!Rosalind!Franklin!was!a!skilled!X-ray!crystallographer.!!She!generated!the! image!(Photo!51)!that!Watson!and!Crick!used!to!deduce!the!structure!of!DNA.!!! ! According!to!Watson!and!Crick’s!model:! a.!!How!many!strands!of!nucleic!acids!are!present!in!DNA?!!2! b.!!Are!the!strands!parallel!or!anti-parallel?!!Antiparallel! c.!!What!is!the!shape!of!the!molecule?!!A!double!helix! d.!!Is!the!molecule!right-!or!left-handed?!!The!double!helix!is!right-handed! e.!!What!is!the!distance!between!the!strands!of!DNA?!!2!nm! f.!!!What!is!the!length!of!each!turn!of!the!helix?!!3.4!nm! g.!!How!many!bases!are!found!in!each!turn!of!the!helix?!!10! h.!!Where!are!the!nitrogenous!bases!found!within!Watson!and!Crick’s!model?!!The!bases!are!located!in! the!interior!of!the!helix.!!! i.!!Where!is!the!sugar!phosphate!backbone!located?!!The!sugar!phosphate!backbone!is!on!the!outside!of! the!molecule.! j.!!What!holds!the!two!strands!together?!!Hydrogen!bonding!between!a!purine!and!a!pyrimidine.!!An! adenine!on!one!strand!will!pair!with!a!thymine!on!the!other!strand.!!Similarly,!a!guanine!on!one!strand! will!pair!with!a!cytosine!on!the!other!strand.!

* 5.!!Meselson!and!Stahl!conduced!an!elegant!experiment!using!two!isotopes!of!nitrogen!(15N!–!heavy!and! 14 N!light)!to!label!DNA!in!E.*coli.!Why!did!they!use!radioactive!N!to!label!DNA?!!Nitrogen!atoms!are! abundant!in!the!nitrogenous!bases!of!DNA.!!! What!was!the!purpose!of!their!experiment?!!The!purpose!of!the!experiment!was!to!determine!if!DNA! replication!occurred!via!the!conservative,!semiconservative,!or!dispersive!model!of!DNA!replication.!!!! Briefly!outline!the!experiment.!!E.*coli*bacteria!was!cultured!for!several!generations!in!medium! containing!nucleotide!precursors!labeled!with!15N!–!heavy!isotope.!!The!cells!were!transferred!to!new! medium!containing!only!nucleotide!precursors!labeled!with!14N!–!light!isotope.!Cells!were!removed!after! 20!and!40!minutes!of!growth!and!the!DNA!was!extracted!and!centrifuged!within!a!cesium!gradient.!!! ! Below!is!a!picture!indicating!the!location!of!the!DNA!in!the!test!tubes!after!centrifugation.! !

! ! Why!is!there!only!one!band!of!DNA!after!one!round!of!DNA!replication?!!There!is!only!one!band!of!DNA! because!the!DNA!contains!one!strand!of!heavy!N!(parental!strand)!and!one!strand!of!light!N!(daughter!

strand).!!The!controls!each!contain!two!strands!of!heavy!N!(lower!band)!or!two!strands!of!light!N! (highest!band).!!! Why!are!there!two!band!of!DNA!after!two!round!of!DNA!replication?!!The!DNA!strands!from!the!first! round!of!synthesis!separated!(one!labeled!with!heavy!N!and!one!labeled!with!light!N).!!These!strands! served!as!templates!for!the!synthesis!of!two!new!strands!of!DNA!in!the!presence!of!the!light!N.!!The! lower!band!of!DNA!consisted!of!one!strand!of!original!heavy!N!and!one!strand!of!light!N.!!The!higher! band!of!DNA!consisted!of!two!stands!of!light!N.!!! Which!model!of!DNA!replication!was!correct?!!The!semiconservative! ! 6.!!Why!is!DNA!replication!described!as!both!quick!and!accurate?!!!E.*coli*can!copy!its!DNA!and!divide!in! less!than!1!hour;!human!cells!take!a!bit!longer!(2-3!hours).!!DNA!replication!generates!very!few!errors!(1! mistake!per!10!billion!nucleotides).!!! What!is!the!origin!of!replication?!!The!origin!of!replication!is!a!specific!sequence!of!DNA!where!DNA! replication!begins.!!! Why!does!bacteria!have!only!one!origin!of!replication?!!The!bacterial!chromosome!is!circular!and!DNA! replication!proceeds!in!both!directions!away!from!the!origin!of!replication.!!See!drawing!below:!

! ! 7.!!Why!do!eukaryotic!cells!have!multiple!copies!of!the!origin!of!replication!on!the!DNA!found!in!its! chromosomes?!!In!eukaryotic!cells,!chromosomes!are!large!and!linear.!!Multiple!copies!of!the!origin!of! replication!help!speed!up!the!process!of!DNA!replication.!!Just!like!in!bacteria,!DNA!replication!proceeds! in!both!directions!away!from!the!origin!of!replication,!generating!a!replication!bubble.!!!Eventually!the! bubbles!will!meet,!fuse,!and!form!two!daughter!DNA!strands!! !

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8.!!Below!is!a!list!of!all!the!proteins!involved!in!DNA!replication.!!Match!the!protein!with!the!description! that!best!fits!its!function.!! Protein( Function( (!!e!!)!DNA!polymerase!III!(bacteria)!!! a. Enzyme!that!unwinds!the!parental!double!helix! (!!h!)!DNA!ligase! b. Protein!that!stabilize!the!unwound!template!strands! (!!g!!)!Sliding!clamp!protein! c. Enzyme!that!breaks,!swivels,!and!rejoins!the!parental!DNA! ahead!of!the!replication!fork!and!relieves!the!strain!caused!by! unwinding! (!!c!!)!Topoisomerase:! d. Enzyme!that!synthesizes!RNA!primers!for!each!Okazaki!fragment! (!a!!!)!Helicases:! e. Enzyme!that!catalyzes!the!addition!of!a!nucleoside!triphosphate! to!the!3’!end!of!a!growing!DNA!strand!! (!!f!!)!DNA!polymerase!I!(bacteria)!!! f. Enzyme!that!removes!the!primer!from!the!5’!end!of!an!Okazaki! fragment!(or!leading!strand)!and!replaces!it!with!DNA! nucleotides! (!!d!!)!Primase:! g. Protein!that!moves!DNA!polymerase!III!along!the!DNA!as!it!adds! nucleotides!to!the!3’!end!of!the!new!strand! (!!b!!)!Single-strand!binding!proteins! h. Enzyme!that!joins!the!3’!end!of!one!Okazaki!fragment!to!the!5’! end!of!another!Okazaki!fragment! ! 9.!!If!DNA!replication!is!a!classic!example!of!an!anabolic!reaction!(building!complex!molecule!from!simple! monomers),!why!is!DNA!polymerization!a!coupled!exergonic!reaction?''Because!when!the!nucleotide! triphosphate!is!added!to!the!3’!end!of!the!daughter!strand,!pyrophosphate!(P-P)!is!released.!!This! molecule!is!very!unstable!due!to!the!arrangement!of!the!negatively!charged!oxygen!molecules!within! the!two!phosphate!groups.!!The!breakdown!of!pyrophosphate!to!2!inorganic!phosphates!is!very! exergonic!and!releases!a!large!amount!of!energy!that!helps!drive!the!polymerization!reaction.! ! 10.!!Label!the!following!letters!in!the!diagram.!!See*page*324*of*Campbell.!

! Why!is!it!necessary!for!the!lagging!strand!of!DNA!to!be!synthesized!in!a!discontinuous!manner?!!!DNA! synthesis!occurs!on!both!strands!in!the!directions!away!from!the!origin!of!replication,!generating!a! replication!bubble.!!!DNA!synthesis!occurs!at!the!replication!forks!in!the!5’→3’!direction.!!One!strand!will! be!synthesized!continuously!(leading!strand).!!However!the!opposite!strand!(lagging!strand)!must!be! synthesized!in!small!fragments!(Okasaki).!!These!fragments!are!synthesized!in!the!5’→3’!direction!but!

the!overall!direction!of!synthesis!is!away!from!the!origin!of!replication.!!Remember!that!DNA!polymerase! can!only!add!nucleotide!triphosphates!to!the!3’!end!of!a!growing!DNA!strand.! ! 11.!!DNA!replication!is!very!accurate!with!an!error!rate!of!1!in!10!billion!nucleotides.!!One!reason!that! this!error!rate!is!so!low!is!that!DNA!polymerase!III!will!proofread!each!base!that!is!added!and! “autocorrect”!mismatched!nucleotides.!!What!are!some!other!factors!that!can!alter!DNA!sequences?!!! Harmful!Chemicals,!Radiation!emissions,!X-rays,!Ultraviolet!light,!and!Molecules!in!Cigarette!smoke.!! How!does!the!cell!repair!damaged!or!mismatched!DNA!nucleotides?!!Both!bacterial!and!eukaryotic!cells! have!mismatch!repair!systems!that!consist!or!over!100!different!enzymes.!!Nucleases!function!to!remove! a!piece!of!DNA!that!includes!the!mismatch.!!DNA!polymerase!fills!in!the!missing!nucleotides!(DNA! polymerase!I!in!bacteria)!and!DNA!ligase!seals!the!free!end!of!the!new!DNA!to!the!old!DNA,!making!the! strand!complete.!!! ! 12.!!What!is!a!telomere?!!A!telomere!is!a!repetitive!DNA!sequence!(TTAGGG)!at!the!end!of!a!eukaryotic! chromosome’s!DNA!molecule!that!protects!the!organism’s!genes!from!being!eroded!during!successive! rounds!of!replication.!!! Why!do!the!ends!of!chromosomes!erode!during!several!rounds!of!DNA!replication?!!The!RNA!primer!at! the!very!end!of!the!lagging!s trand!of!DNA!is!removed!by!DNA!polymerase!I.!!However,!DNA!polymerase!I! cannot!replace!the!RNA!nucleotides!with!DNA!nucleotides!because!there!is!no!3’!nucleotide!to!add!to!at! the!ends!of!the!chromosomes.!!Remember,*DNA*polymerase*can*only*add*DNA*nucleotides*to*a*3’*end*of* an*RNA*primer*or*growing*DNA*strand.!!Repeated!rounds!of!DNA!replication!produce!shorter!and!shorter! DNA!molecules!with!uneven!(staggered)!ends.! ! Why!is!the!DNA!strand!from!a!muscle!cell!longer!than!the!DNA!strand!from!an!epithelial!cell!lining!the! stomach?!!Because!a!muscle!cell!does!not!reproduce!and!an!epithelial!lining!the!wall!of!the!stomach!cell! reproduces!every!three!days.!!! What!is!the!function!of!telomerase?!!An!enzyme!that!catalyzes!the!lengthening!of!telomeres!in! eukaryotic!germ!cells?!!! Do!bacteria!have!telomeres?!!No,!bacterial!DNA!is!circular!and!thus!they!have!a!3’!end!to!add! nucleotides!to!after!the!RNA!was!removed!from!the!primer.! ! 13.!!Below!is!a!figure!depicting!chromatin!packaging!in!a!eukaryotic!chromosome.!!!

! ! What!is!the!name!of!the!type!of!protein!that!is!responsible!for!the!first!level!of!packaging!in!chromatin?!! Histone!proteins.!!What!is!a!nucleosome?!!The!basic!unit!of!DNA!packaging.!!It!consists!of!DNA!wrapped!

twice!around!a!core!of!eight!histone!proteins!(bead).!!The!DNA!between!nucleosomes!is!called!linker!DNA.!! When!during!the!cell!cycle!is!DNA!free!of!theses!histone!proteins?!!Histones!leave!the!DNA!only!briefly! during!the!S!phase!of!interphase!during!DNA!replication.!!The!histones!also!leave!briefly!during! transcription.!!When!during!the!cell!cycle!is!chromatin!(euchromatin)!usually!30!nm!in!diameter?!!During!G1! and!G2!of!interphase.!!When!during!the!cell!cycle!is!all!the!chromatid!700!nm!in!diameter.!!During! metaphase!when!the!chromosomes!are!fully!condensed.!!Some!G1!and!G2!interphase!chromatin!is! condensed!to!700!nM.!!What!is!the!name!of!this!type!of!chromatin!and!where!within!an!interphase! chromosome!is!it!located.!!Heterochromatin!is!condensed!to!700!nM!and!it!is!located!in!the!centromere! and!telomere!regions!of!a!chromosome.!!This!type!of!chromatin!in!not!accessible!to!transcriptional! machinery!and!is!therefore!not!transcribed.!! !...