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7/24/2019 BIOTEK3 DNAReplication
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DNA ReplicationDNA Replication
AP Biology
Unit 3
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DNA Structure
Double Helix (2 strands of DNA)
Complementary strands pair up (A & T C
& !)" #ydro$en bonds
Strands are antiparallel (% and ' ends)
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DNA eplication
#en DNA is copieddurin$ S *#ase of
+nterp#ase
,asic Concept - createa ne. strand by
matc#in$ nucleotides
to an existin$ strand
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DNA eplication
eplication is semi/conser0ati0e (one strand isold one strand ne.)
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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
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!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
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!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
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Question
#at ind of bonds does Helicase brea9
"Hydro$en bonds
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!eneral *rocess
Step '5 Primasebuilds anNA primer at t#e startin$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
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!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
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Question
#at ot#er en6yme builds similarly to DNA
*olymerase +++9
NA *olymerase (dont mix it up .it#
DNA *olymerase +++
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*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
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>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$ments t#e oppositedirection of replication(opposite direction as#elicase)
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Questions
Ho. many primers does t#e leadin$ strand
need9
"1nly 3" to start replication
Ho. many primers does t#e la$$in$ strand
need9
"?any " one for eac# 1a6ai fra$ment
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>a$$in$ Strand
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DNA >i$ase
DNA Ligase seals 1a6ai fra$ments
to$et#er
"@orms co0alent bonds bet.een nucleotides to
create a continuous strand of DNA
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@inis#in$ 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
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@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$et#er
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*uttin$ +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 +
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SSBsDNA
Polymerase III
Primase
Primer
DNA Pol
III LaggingStrand
DNA
Polymerase I
Leading Strand
DNA Ligase
Helicase