biotek3 dnareplication

7/24/2019 BIOTEK3 DNAReplication

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DNA ReplicationDNA Replication

AP Biology

Unit 3


2/20

DNA Structure

Double Helix (2 strands of DNA)

Complementary strands pair up (A & T C

& !)" #ydro$en bonds

Strands are antiparallel (% and ' ends)


3/20

DNA eplication

#en DNA is copieddurin$ S *#ase of

+nterp#ase

,asic Concept - createa ne. strand by

matc#in$ nucleotides

to an existin$ strand


4/20

DNA eplication

eplication is semi/conser0ati0e (one strand isold one strand ne.)


5/20

1ri$ins of eplication

#ere DNA eplication

starts

Differs bet.een

or$anisms

"*roaryotes - 3 ori$in of

replication

"4uaryotes - manydifferent ori$ins of

replication


6/20

!eneral *rocess of DNA eplication

Step 35 Initiator Proteinsbind to ori$ins of

replication to be$in replication

"Attracts ot#er en6ymes in0ol0ed in replication

process


7/20

!eneral *rocess

Step 2:

" DNA Helicaseseparates t#e DNA #elix

" Topoisomerase (Gyrase)pre0ents7o0er.indin$8 of DNA

" Single Stranded Binding Proteins

(SSBs)pre0ent double #elix from

reformin$ temporarily


8/20

Question

#at ind of bonds does Helicase brea9

"Hydro$en bonds


9/20

!eneral *rocess

Step '5 Primasebuilds anNA primer at t#e startin$from t#e % end of t#e ne.

DNA strand":ses t#e ' end of existin$

DNA strand

"Why? ,ecause t#e DNA*olymerase +++ (main DNA

buildin$ en6yme) needssomet#in$ to build off of

3 5

5

Primase

RNA Primer

DNA Polymerase III


10/20

!eneral *rocess

Step ;5 DNA

Polymerase IIIbuilds

t#e ne. strand of

DNA in a % to 'direction

"#at inds bonds are

bein$ formed to maea ne. strand of DNA9

"Co0alent bonds


11/20

Question

#at ot#er en6yme builds similarly to DNA

*olymerase +++9

NA *olymerase (dont mix it up .it#

DNA *olymerase +++


12/20

*roblem=

How can both strans o! DNA be replicate

in a "#$ 3# irection at the sa%e ti%e they

are antiparallel?

Answer& leaing an lagging strans


13/20

>eadin$ and >a$$in$ Strands

>eadin$ strand issynt#esi6ed continuouslyin t#e direction ofreplication ($oes in t#esame direction as #elicase)

>a$$in$ strand issynt#esi6ed in s#ort

fra$ments t#e oppositedirection of replication(opposite direction as#elicase)


14/20

Questions

Ho. many primers does t#e leadin$ strand

need9

"1nly 3" to start replication

Ho. many primers does t#e la$$in$ strand

need9

"?any " one for eac# 1a6ai fra$ment


15/20

>a$$in$ Strand


16/20

DNA >i$ase

DNA Ligase seals 1a6ai fra$ments

to$et#er

"@orms co0alent bonds bet.een nucleotides to

create a continuous strand of DNA


17/20

@inis#in$ DNA eplication

*roblem 35 T#ere are still NA

nucleotides in t#e DNA (primers)

Solution - DNA *olymerase + cuts out t#e

NA nucleotides and replaces t#em .it#DNA


18/20

@inis#in$ DNA eplication

*roblem 25 1a6ai fra$ments and bases

replaced DNA *olymerase + are not

attac#ed to rest of DNA Solution - DNA >i$ase seals e0eryt#in$

to$et#er


19/20

*uttin$ +t All To$et#er

>abel t#e dia$ram on *a$e B .it# t#e

follo.in$ terms5

/ SS,s / DNA >i$ase

/ >eadin$ Strand / >a$$in$ Strand

/ Helicase / *rimase

/ DNA *olymerase +++ / *rimer

/ DNA *olymerase +


20/20

SSBsDNA

Polymerase III

Primase

Primer

DNA Pol

III LaggingStrand

DNA

Polymerase I

Leading Strand

DNA Ligase

Helicase

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