SBI 4U
DATE: ____________________
DNA REPLICATION
Recall:
Before a cell can divide, it must first make a copy of each of its _________________________
DNA Replication
 Two DNA molecules are made from __________________
 Each new DNA molecule (double helix) will have one strand of DNA from the ______________ molecule and one
___________ strand.
o i.e. it is ______________________________
 Parent DNA molecule and two daughter molecules are ________________ (same nucleotides in same order)
 Recall: Chargaff’s Rule
o Adenine binds with Thymine
o Cytosine binds with Guanine
o Therefore, if you know the order of one strand, you know the order of the other
SEPARATING THE DNA STRANDS
1. Replication begins when proteins bind at a specific site on DNA – _______________________
2. DNA ____________ “unzips” or “unwinds” the DNA helix by breaking the Hydrogen bonds between nitrogenous
bases that holds the two strands together.
3. ___________________________________ (SSBs) prevent the complementary strands from _______________
(pairing together)
o This allows the strands to remain as _________________ for new DNA synthesis
4. DNA _______________ (in prokaryotes) and similar enzymes in Eukaryotes helps relieve tension on the
unwinding DNA
DIRECTIONALITY
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Replication begins in two directions from the origin as a region of the DNA is unwound
DNA can’t be completely unwound due to size, so replication begins as soon as an opening is available
Replication fork________________________________________________________________
o Replication goes ______________ the direction of the fork in one strand, and ___________ from it in
another strand (leading vs. lagging strand…stay tuned  )
o Can be more than one in eukaryotes due to size
Replication bubble  ____________________________________________________________
SBI 4U
DATE: ____________________
BUILDING THE COMPLEMENTARY STRANDS
Important:
 DNA is synthesized in the ___________ direction ONLY!!
o i.e. _______________________ can only travel in the direction of 5’-3’;
o Free bases are added via the ________ of a growing DNA strand via ________________
Step One: Priming Replication using RNA primase
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_______________ binds at the initiation point of the __________________
DNA polymerase cannot initiate a polynucleotide strand; it can only add to the 3’
end of an ______________________ strand
o Thus __________________ helps to lay down an _________________ (a
series of complementary RNA nucleotides)
o the primer _______ be laid down _________
o They are “____________;” can be removed later
_____________________________ can start elongation of the new strand by adding
free ________________________________ from cytoplasm to the elongating strand
DNA Polymerase III uses the ___________ from breaking the bond b/w the first and
second ________________ to drive the condensation rxn that adds a nucleotide to
the growing strand
Step Two: Elongation
The elongation process is different for the 5'-3' and 3'-5' template
Leading
5'-3' Template:
 The daughter strand that uses the 5'-3' template is called _____________________ because DNA Polymerase III
can "read" the template and ________________________ adds nucleotides
o i.e. DNA polymerase is traveling continuously in the _______ direction of the new strand
Lagging
3'-5'Template:
 The 3'-5' template ___________ be "read" by DNA Polymerase III (***DNA polymerase only travels in the 5’-3’
direction)
 Strand is synthesized ___________________ in short fragments in the opposite direction to the replication fork
 called _________________________
 As a replication bubble opens, a polymerase molecule can work its way from the ____________
__________________________________________
 As the bubble _____________ another segment can be made
 Therefore, the lagging strand is synthesized in a series of
segments
o Called __________________________
SBI 4U
DATE: ____________________
Leading vs. Lagging Strand
Step 3: Cleanup
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___________________________ removes RNA __________ from both leading and lagging strands and replaces
them with appropriate _______________________________
Since lagging strand is built in short segments, _____________ (enzyme) joins Okazaki fragments into one strand
by _______________________________
Two ______ double-stranded molecules each twist into two ___________________
SBI 4U
OVERVIEW OF REPLICATION
RE-EMPHASIZING THE SEMI-CONSERVATIVE MODEL
One strand acts as a ______________ to make a new strand.
Process is ________________________ because each daughter strand
is paired with a parent strand.
One old and one new.
DATE: ____________________