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 Thymineo Cytosine binds with Guanineo 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

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 J )

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

_______________ binds at the initiation point of the __________________ DNA polymerase cannot initiate a polynucleotide strand; it can only add to the 3’

end of an ______________________ strando 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

segmentso Called __________________________

SBI 4U DATE: ____________________

Leading vs. Lagging Strand

Step 3: Cleanup

___________________________ 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 DATE: ____________________

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.