pierce sm chapter10

8/18/2019 Pierce Sm Chapter10

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Chapter Ten: DNA: The Chemical Nature of the Gene


COMPREHENSION QUESTIONS

*1. What three general characteristics must the genetic material possess?

(1) The genetic material must contain complex information.(2) The genetic material must replicate or be replicated faithfully.

(3) The genetic material must encode the phenotype.

2. Briefl outline the histor of our !no"le#ge of the structure of DNA until the time

of Watson an# Cric!. Which #o ou thin! "ere the principle contri$utions an#

#e%elopments?

1869 !ohann "riedrich #iescher isolates nuclei from $hite blood cells andextracts a substance that $as slightly acidic and rich in phosphorous. %e calls

it nuclein.

&ate 18''s lbrecht ossel determines that *+ contains the four nitrogenous

bases adenine, guanine, cytosine, and thymine.192's -hoebus aron &eine discoers that *+ consists of repeating units, each

consisting of a sugar, a phosphate, and a nitrogenous base.19/' 0r$in hargaff formulates hargaffs rules (T and 4).

195 7illiam shbury begins studying *+ structure using ray diffraction.

19/1:19/3 ;osalind "ran


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transforming material and demonstrate that it had chemical properties similar to

*+.

*,. o" #i# ershe an# Chase sho" that DNA is passe# to ne" phages in phage

repro#uction?

%ershey and hase used the radioactie isotope32

- to demonstrate that *+ is passed to ne$ phage particles during phage reproduction. The progeny phage

released from bacteria infected $ith 32 -labeled phages emitted radioactiity from32 -. The presence of the 32 - in the progeny phage indicated that the infecting phagehad passed *+ on to the progeny phage.

-. Wh "as Watson an# Cric!s #isco%er so important?

>y deciphering the structure of the *+ molecule, 7atson and ric< proided the foundation for molecular studies of the genetic material or *+, allo$ing

scientists to discern ho$ genes function to produce phenotypes. Their model also

suggested a possible mechanism for the replication of *+ that $ould ensure the

fidelity of the replicated copies.

*/. Dra" an# la$el the three parts of a DNA nucleoti#e.The three parts of a *+ nucleotide are phosphate, deoxyribose sugar, and a

nitrogenous base.

0. o" #oes an NA nucleoti#e #iffer from a DNA nucleoti#e?

*+ nucleotides, or deoxyribonucleotides, hae a deoxyribose sugar that lac


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purine consists of a sixsided ring attached to a fiesided ring. pyrimidine

consists of only a sixsided ring. An both *+ and ;+, the purines found are

adenine and guanine. *+ and ;+ differ in their pyrimidine content. The pyrimidine cytosine is found in both ;+ and *+. %o$eer, *+ contains the

pyrimidine thymine, $hereas ;+ contains the pyrimidine uracil but not thymine.

*1. Dra" a short segment of a single polnucleoti#e stran#3 inclu#ing at least three

nucleoti#es. 4n#icate the polarit of the stran# $ la$eling the ,5 en# an# the &5 en#.

11. Which $ases are capa$le of forming h#rogen $on#s "ith each another?

denine is capable of forming t$o hydrogen bonds $ith thymine. 4uanine iscapable of forming three hydrogen bonds $ith cytosine.

*12. What is local %ariation in DNA structure an# "hat causes it?Bince *+ is not a static, rigid structure that is inariant, the local ariation in

*+ structure refers to the actual ariations that exist in a *+ molecule. "or

instance, >*+ is described as haing an aerage of 1' bases per turn. %o$eer,the actual alues may be less than or greater than 1', depending on the

enironmental conditions.

1&. What are some of the important genetic implications of the DNA structure?

1&1


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;eferring bac< to =uestion 1, the structure of *+ gies insight into the three

fundamental genetic processes. The 7atson and ric< model suggests that the

genetic information or instructions are encoded in the nucleotide se=uences. Thecomplementary polynucleotide strands indicate ho$ faithful replication of the

genetic material is possible. "inally, the arrangement of the nucleotides is such that

they specify the primary structure or amino acid se=uence of protein molecules.

*1). What are the ma6or transfers of genetic information?

The maCor transfers of genetic information are replication, transcription, andtranslation. These are the components of the central dogma of molecular biology.

1,. What are hairpins an# ho" #o the form?

%airpins are a type of secondary structure found in single strands of nucleotides. The formation of hairpins occurs $hen se=uences of nucleotides on the single strand are

inerted complementary repeats of one another.

1-. What is DNA methlation? *+ methylation is the addition of methyl groups (:% 3 ) to certain positions on the

nitrogenous bases on the nucleotide.

APPLICATION QUESTIONS AND PROBLEMS

1/. A stu#ent mi'es some heat7!ille# tpe 448 Btreptococcus pneumonia $acteria "ith

li%e tpe 44 $acteria an# in6ects the mi'ture into a mouse. The mouse #e%elops

pneumonia an# #ies. The stu#ent reco%ers some tpe 448 $acteria from the #ea#

mouse. 4t is the onl e'periment con#ucte# $ the stu#ent. as the stu#ent#emonstrate# that transformation has ta!en place? What other e'planations might

e'plain the presence of the tpe 448 $acteria in the #ea# mouse?

+o, the student has not demonstrated that transformation has ta


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Enly *+ $ould contain the isotope 32 -, and only proteins $ould contain the

isotope 3/B.

9$ Coul# the ha%e use# ra#ioacti%e isotopes of car$on 9C an# o'gen 921 g. The human

$o# contains appro'imatel ., g of DNA. o" man nucleoti#e pairs of DNA arein the human $o#? 4f ou assume that all the DNA in human cells is in the B7DNA

form3 ho" far "oul# the DNA reach if stretche# en# to en#?

Af each nucleotide pair of a *+ double helix $eighs approximately 1 I 1' :21 g,and the human body contains './ grams of *+, then the number of nucleotide

pairs can be estimated as ('./ g *+Jhuman)J(1 I 1' :21 gJ nucleotide) / I 1'2'

nucleotides pairsJhuman. *+ that is in > form has an aerage distance of 3.5 nm bet$een each

nucleotide pair. Af a human possesses / I 1'2' nucleotide pairs, then that *+

stretched end to end $ould reach (/ I 1'2' nucleotidesJ human) I (3.5

nmJnucleotide pair) 1. I 1'21 nm or 1. I 1'9


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maCor role in holding the t$o strands together. "inally, the ability of *+ to hae

local ariations in its secondary structure contributes to its stability.

;+ nucleotides or ribonucleotides contain an extra oxygen at the 2@ carbon.This extra oxygen at each nucleotide ma


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guanine bases nor the percentages of guanine and cytosine bases are e=ual,

indicating that the iral genome is singlestranded.

*2,. A B7DNA molecule has 1 million nucleoti#e pairs.

9a o" man complete turns are there in this molecule?

>form *+ contains approximately 1' nucleotides per turn of the helix. > *+ molecule of 1 million nucleotide pairs $ill hae about the follo$ing

number of complete turns (1,''',''' nucleotides)J 1' nucleotidesJturn)

1'',''' complete turns.9$ 4f this same molecule "ere in the 7DNA configuration3 ho" man complete

turns "oul# it ha%e?

Af the same *+ molecule assumes a N*+ configuration then each turn

$ould consist of about 12 nucleotides. The determination of the number ofcomplete turns in the 1 million nucleotide molecule is

(1,''',''' nucleotides)J(12 nucleotides J turn) 83333.3 or 83333 complete

turns.

2-. or entertainment on a ri#a night3 a genetics professor propose# that his chil#ren

#iagram a polnucleoti#e stran# of DNA. a%ing learne# a$out DNA in preschool3his ,7ear7ol# #aughter "as a$le to #ra" a polnucleoti#e stran#3 $ut she ma#e fe"

mista!es. The #aughters #iagram 9represente# here containe# at least 1 mista!es.

<

; D< >

>


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(/) t the 3@ position in both sugars, only hydrogen is attached, as opposed to

an :E% group.

(6) The 1@ carbon of both sugars has an :E% group, as opposed to Cust ahydrogen attached.

9$ Dra" the correct structure for the polnucleoti#e stran#.

O

CH CH

2

CH CHO

CH

2

O

P

O

OH

CH CH

2

CH CH

OCH

2

P O

O

O

O

O

Base

Base

2/. Chapter 1 consi#ere# the theor of the inheritance of acFuire# characteristics an#

note# that this theor is no longer accepte#. 4s the central #ogma consistent "ith thetheor of the inheritance of acFuire# characteristics? Wh or "h not?

The central dogma of molecular biology is not consistent $ith the theory of

inheritance of ac=uired characteristics. The flo$ of information predicted by thecentral dogma is

*+ ;+ -rotein

Ene exception to the central dogma is reerse transcription, $hereby ;+ codes for *+. %o$eer, biologists currently do not


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/@OD4DO3@Punpaired nucleotidesP/@OD4O3@

D

D

4 4

/@D 3@

2+. The follo"ing seFuence is present in one stran# of a DNA molecule:

,5CATTGACCGA&5

Write out the seFuence on the same stran# that pro#uces an in%erte# repeat an#the seFuence on the complementar stran#.

The presence of inerted complementary se=uences on the same strand of a *+

molecule $ill result in a doublestranded *+ molecule containing a palindrome

and could result in the formation of a cruciform structure.

/@OTT44O3@PPPPPPPP../@OT44TT4O3@ 3@O4TT44TO/@PPPPPPPP..3@O44TTO/@

CHALLENGE QUESTIONS

&. 8uppose that an automate#3 unmanne# pro$e is sent into #eep space to search for

e'traterrestrial life. After "an#ering for man light ears among the far reaches of

the uni%erse3 this pro$e arri%es on a #istance planet an# #etects life. The chemicalcomposition of life on this planet is completel #ifferent from that of life on (arth3

an# its genetic material is not compose# of nucleic aci#s. What pre#ictions can ou

ma!e a$out the chemical properties of the genetic material on this planet? lthough the chemical composition of the genetic material may be different *+, it

more than li


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&1. o" might &2; an# &,8 $e use# to #emonstrate that the transforming principle is

DNA? Briefl outline an e'periment that "oul# sho" that DNA an# not protein is

the transforming principle.The first step $ould be to label the *+ and proteins of the donor bacteria cells

$ith 3/B and 32 -. The *+ could be labeled by gro$ing a culture of bacteria in the

presence of32

-. The cells as they replicate ultimately $ill incorporate radioactie phosphorous into their *+. second culture of bacteria should be gro$n in the

presence of 3/B, $hich ultimately $ill be incorporated into proteins.

#aterial from each culture should be used to transform bacteria cells that preiously had not been exposed to the radioactie isotopes. Transformed cells (or

colonies) that $ould be identified by the ac=uisition of a ne$ phenotype should

contain lo$ leels of the radioactie material due to the upta

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