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NUCLEIC ACIDS ARE UNIQUE IN

THEIR ABILITY TO DIRECT THEIROWN REPLICATION FROM

MONOMERS.

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READ THE

BEGINNING

OFCONCEPT

16.1 IN

CAMPBELL,

P. 305.

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GROUP PROJECT:

GRIFFITH AVERY, ET. AL.

HERSHEY AND CHASE

ERWIN CHARGAFF

ROSALIND FRANKLIN

MAURICE WILKINS

JAMES WATSON AND FRANCIS CRICK

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The Search for the Genetic Material

Poster Project

Questions to Answer for the

Presentation:

1.What were the scientists actuallylooking for in their research?

2.What did they do in their

experiment?

3.How did it impact understanding of

DNA?

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Figure 16-01

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LE 16-2

Living S cells

(control)

Living R cells

(control)

Heat-killed

S cells (control)

Mixture of heat-killed

S cells and living

R cells

Mouse dies

Living S cells

are found in

blood sample

Mouse healthy Mouse healthy Mouse dies

RESULTS

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LE 16-3

Bacterialcell

Phage

head

Tail

Tail fiber

DNA

100nm

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LE 16-4

Bacterial cell

Phage

DNA

Radioactive

protein

Emptyprotein shell

PhageDNA

Radioactivity

(phage protein)

in liquid

Batch 1:

Sulfur (35S)

RadioactiveDNA

Centrifuge

Pellet (bacterialcells and contents)

PelletRadioactivity

(phage DNA)

in pellet

Centrifuge

Batch 2:Phosphorus (32P)

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Portrait of Erwin Chargaff. 1930

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LE 16-6

Franklins X-ray diffraction

photograph of DNA

Rosalind Franklin

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LE 16-7c

Space-filling model

LE 16 7

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LE 16-7

5 end

3 end

5

end

3 end

Space-filling modelPartial chemical structure

Hydrogen bond

Key features of DNA structure

0.34 nm

3.4 nm

1 nm

THESE MEASUREMENTS

ARE IMPORTANT AND DO

NOT VARY!

NOTICE THE NUMBER OF HYDROGEN

BONDS BETWEEN THE BASE PAIRS

ABOVE?

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LE 16-5Sugarphosphate

backbone

5

end

Nitrogenousbases

Thymine (T)

Adenine (A)

Cytosine (C)

DNA nucleotidePhosphate

3 endGuanine (G)

Sugar (deoxyribose)

1. HOW ARE THE

NUCLEOTIDES THE

SAME?

2. WHAT ARE THETHREE PARTS OF A

NUCLEOTIDE?

3. HOW ARE THE

NUCLEOTIDES

DIFFERENT?4. HOW DOES THE 5

END DIFFER FROM

THE 3 END?

5. WHICH ONES ARE

PURINES? WHICHONES ARE

PYRIMIDINES?

LE 16 7b

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LE 16-7b

5 end

3 end

5 end

3 end

Partial chemical structure

Hydrogen bond

EXPLAIN WHAT

IS MEANT BY

THE TWO SIDES

OF THE DOUBLE

HELIX BEINGANTIPARALLEL.

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For a great review of DNA structure and

replication go to Biocoach athttp://www.phschool.com/science/biology_place/biocoach/dnarep/intro.html
http://www.phschool.com/science/biology_place/biocoach/dnarep/intro.htmlhttp://www.phschool.com/science/biology_place/biocoach/dnarep/intro.html

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LE 16 9 1

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LE 16-9_1

The parent molecule hastwo complementarystrands of DNA. Each baseis paired by hydrogenbonding with its specificpartner, A with T and G withC.

LE 16-9 4

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LE 16-9_4

The parent molecule hastwo complementarystrands of DNA. Each baseis paired by hydrogenbonding with its specificpartner, A with T and Gwith C.

The first step in replicationis separation of the twoDNA strands.

Each parental strand nowserves as a template thatdetermines the order ofnucleotides along a new,complementary strand.

The nucleotides areconnected to form thesugar-phosphate back-bones of the new strands.Each daughter DNAmolecule consists of oneparental strand and onenew strand.

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WHAT WERE THE THREE

HYPOTHESES/MODELS

CONSIDERED FOR THE

PROCESS OF DNA

REPLICATION?

LE 16-10

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LE 16 10

Conservative

model. The two

parental strands

reassociate after

acting as

templates for

new strands,thus restoring

the parental

double helix.

Semiconservative

model. The two

strands of the

parentalmolecule

separate, and

each functions as

a template for

synthesis of a

new, comple-

mentary strand.

Dispersive model.

Each strand ofboth daughter

molecules

contains

a mixture of

old and newly

synthesized

DNA.

Parent cellFirstreplication

Secondreplication

LE 16-10LE 16-11

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LE 16 10

Conservative

model. The two

parental strands

reassociate after

acting as

templates for

new strands,thus restoring

the parental

double helix.

Semiconservative

model. The two

strands of the

parentalmolecule

separate, and

each functions as

a template for

synthesis of a

new, comple-

mentary strand.

Dispersive model.

Each strand ofboth daughter

molecules

contains

a mixture of

old and newly

synthesized

DNA.

Parent cellFirstreplication

Secondreplication

LE 16 11

Bacteria

cultured in

medium

containing15N

DNA sample

centrifuged

after 20 min

(after first

replication)

DNA sample

centrifuged

after 40 min

(after second

replication)

Bacteria

transferred to

medium

containing14N

Less

dense

More

dense

Conservative

model

First replication

Semiconservative

model

Second replication

Dispersive

model

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LE 16-11a

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LE 16 11a

Bacteria

cultured inmedium

containing15N

DNA sample

centrifuged

after 20 min(after first

replication)

DNA sample

centrifuged

after 40 min(after second

replication)

Bacteria

transferred tomedium

containing14N

Less

dense

More

dense

LE 16-11b

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Conservative

model

First replication

Semiconservative

model

Second replication

Dispersive

model

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For more details of Meselson and

Stahls experiment seehttp://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.h

tml
http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.htmlhttp://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.htmlhttp://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.htmlhttp://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.html

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THE STEPS OF

REPLICATION IN E.

COLI

MOST OF THE PROCESS IS FUNDAMENTALLY

SIMILAR IN PROKARYOTES AND IN

EUKARYOTES.

LE 16-12

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In eukaryotes, DNA replication begins at many sitesalong the giant DNA molecule of each chromosome.

Two daughter DNA molecules

Parental (template) strand

Daughter (new) strand0.25 m

Replication fork

Origin of replication

Bubble

In this micrograph, three replicationbubbles are visible along the DNAof a cultured Chinese hamster cell(TEM).

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The replisomeis a complex

molecular machine that carries

out replication of DNA. It is

made up of a number of

subcomponents that each

provide a specific function

during the process of replication.

LE 16-13
http://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/DNA

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New strand

5

end

PhosphateBase

Sugar

Template strand

3

end 5 end 3

end

5

end

3

end

5

end

3

end

Nucleoside

triphosphate

DNA polymerase

Pyrophosphate

WHAT PROVIDES THE ENERGY TO ADD NEW NUCLEOTIDES?

LE 16-14

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Parental DNA

5

3

Leading strand

3

5

3

5

Okazaki

fragmentsLagging strand

DNA pol III

Template

strand

Leading strand

Lagging strand

DNA ligaseTemplate

strand

Overall direction of replication

WHATS THE

DIFFERENCEBETWEEN A

LEADING AND

A LAGGING

STRAND?

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leading strand

The new continuous complementary DNA strand synthesized along the template strand

in the mandatory 5 ( 3 direction.

lagging strand

A discontinuously synthesized DNA strand that elongates in a direction away from thereplication fork.

Okazaki fragment

A short segment of DNA synthesized on a template strand during DNA replication. ManyOkazaki fragments make up the lagging strand of newly synthesized DNA.

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HOW DOES THE SYNTHESIS

OF THE

LAGGING STRAND WORK?

LE 16-15_1

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53

Primase joins RNA

nucleotides into a primer.

Templatestrand

5 3


LE 16-15_2P i j i RNA

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53

Primase joins RNA


Template

strand

5 3


RNA primer3

5

35

DNA pol III addsDNA nucleotides tothe primer, formingan Okazaki fragment.

LE 16-15_3P i j i RNA

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53

Primase joins RNA


Template

strand

5 3


RNA primer3

5

35


Okazaki

fragment3

5

5

3

After reaching thenext RNA primer (not

shown), DNA pol IIIfalls off.

LE 16-15_4Primase joins RNA

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53

Primase joins RNA


Template

strand

5 3


RNA primer3

5

35


Okazaki

fragment3

5

5

3



33

5

5

After the second fragment isprimed, DNA pol III adds DNAnucleotides until it reaches the

first primer and falls off.


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53

Primase joins RNA


Template

strand

5 3


RNA primer3

5

35


Okazaki

fragment3

5

5

3



33

5

5

After the second fragment isprimed, DNA pol III adds DNAnucleotides until it reaches thefirst primer and falls off.

33

5

5

DNA pol I replacesthe RNA with DNA,adding to the 3 endof fragment 2.


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53

Primase joins RNA


Template

strand

5 3


RNA primer3

5

35


Okazaki

fragment3

5

5

3



33

5

5

After the second fragment isprimed, DNA pol III adds DNAnucleotides until it reaches thefirst primer and falls off.

33

5

5

DNA pol I replacesthe RNA with DNA,adding to the 3 endof fragment 2.

3

3

5

5

DNA ligase forms abond between the newestDNA and the adjacent DNAof fragment 1.

The laggingstrand in the regionis now complete.

LE 16-16

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5

3

Parental DNA

3

5


DNA pol III

Replication fork

Leadingstrand

DNA ligase

Primase

OVERVIEW

PrimerDNA pol III

DNA pol I

Lagging

strand

Lagging

strand

Leading

strand

Leading

strand

Lagging

strandOrigin of replication

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For a review of DNA replication and

interactive quiz questions go tohttp://www.wiley.com/college/pratt/0471393878/instructor/animations/dna_replication/index.html
http://www.wiley.com/college/pratt/0471393878/instructor/animations/dna_replication/index.htmlhttp://www.wiley.com/college/pratt/0471393878/instructor/animations/dna_replication/index.htmlhttp://www.wiley.com/college/pratt/0471393878/instructor/animations/dna_replication/index.htmlhttp://www.wiley.com/college/pratt/0471393878/instructor/animations/dna_replication/index.html

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http://www.nature.com/nrc/journal/v1/n1/animation/nrc1001-022a_swf_MEDIA1.html

CHECK THIS OUT
http://www.nature.com/nrc/journal/v1/n1/animation/nrc1001-022a_swf_MEDIA1.htmlhttp://www.nature.com/nrc/journal/v1/n1/animation/nrc1001-022a_swf_MEDIA1.htmlhttp://www.nature.com/nrc/journal/v1/n1/animation/nrc1001-022a_swf_MEDIA1.htmlhttp://www.nature.com/nrc/journal/v1/n1/animation/nrc1001-022a_swf_MEDIA1.html

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PROOFREADING AND

REPAIRING DNA

LE 16-17

A thymine dimer

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DNA

ligase

DNA

polymerase

DNA ligase seals the

free end of the new DNA

to the old DNA, making the

strand complete.

Repair synthesis by

a DNA polymerase

fills in the missing

nucleotides.

A nuclease enzyme cuts

the damaged DNA strandat two points and the

damaged section is

removed.

Nuclease

A thymine dimer

distorts the DNA molecule.

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LE 16-18

5

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End of parental

DNA strands

5

3

Lagging strand 5

3

Last fragment

RNA primer

Leading strand

Lagging strand

Previous fragment

Primer removed but

cannot be replaced

with DNA because

no 3

end availablefor DNA polymerase

5

3

Removal of primers and

replacement with DNA

where a 3

end is available

Second round

of replication

5

3

5

3

Further rounds

of replication

New leading strandNew leading strand

Shorter and shorter

daughter molecules

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telomerase

An enzyme that catalyzes the lengthening of

telomeres in germ cells. The enzyme includes a

molecule of RNA that serves as a template for

new telomere segments.

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THE CANCER CONNECTION

1. NORMAL SHORTENING OF

TELOMERES MAY PROTECT FROM

CANCER; LIMITS NUMBER OF TIMES

A SOMATIC CELL CAN DIVIDE

2. TELOMERASE ACTIVITY FOUNDIN SOME CANCEROUS SOMATIC

CELLS; ALLOWS CANCER CELLS TO

PERSIST?

3. TELOMERASE A TARGET FOR

CANCER DIAGNOSIS AND

CHEMOTHERAPY?

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histone

A small protein with a high proportion of positively chargedamino acids that binds to the negatively charged DNA and

plays a key role in its chromatin structure.

nucleosome

The basic, bead-like unit of DNA packaging in eukaryotes,

consisting of a segment of DNA wound around a protein corecomposed of two copies of each of four types of histone.

LE 19-2a

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DNA double helix

Histone

tails

His-

tones

Linker DNA

(string)

Nucleosome

(bead)

10 nm

2 nm

Histone H1

Nucleosomes (10-nm fiber)

A FIFTH TYPE; NEEDED FOR

FURTHER PACKING

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LE 19-2c

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300 nm

Loops

Scaffold

Protein scaffold

Looped domains (300-nm fiber)

LE 19-2d

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Metaphase chromosome

700 nm

1,400 nm

SO WE CAN SEE HOW DNA IS PACKED UP FOR MITOSIS OR

MEIOSIS, BUT WHEN ELSE MIGHT IT BE USEFUL TO PACK OR

UNPACK DNA?

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SEE ACTIVITY ON DNA

PACKING ON THE

CAMPBELL WEBSITE

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chromatin

The complex of DNA and proteins that makes up a eukaryotic

chromosome. When the cell is not dividing, chromatin exists

as a mass of very long, thin fibers that are not visible with alight microscope.

heterochromatin

Nontranscribed eukaryotic chromatin that is so highlycompacted that it is visible with a light microscope during

interphase.

euchromatinThe more open, unraveled form of eukaryotic chromatin that

is available for transcription.

Chapter 16 2013

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