Chapter 12 DNA Replication Manipulation S Phase of Cell Cycle Happens during Mitosis Meiosis only DNA transcription translation is a different process I Review of DNA Structure 2 nucleotides are linked by series of covalent bonds called a phosphodiester bond C O P O C A The Backbone 1 Linear strand of alternating phosphate sugar groups 2 Negatively charged 3 Tail end phosphate not connected to a sugar will be HPO4 H attached to top O instead of PO4 see diagram 4 All sugars in strand are oriented in same direction 5 3 or 3 5 5 Strand has polarity or direction B Base Sequence C Double helix 1 Variable part of DNA holds info 1 2 strands stay together by H bonds that form between complimentary bases 1 purine 1 pyrimidine a A T G C i This specificity is what keep width of DNA constant b Bases also interact noncovalently with the ones above below and stack tightly group which stabilizes helix II How DNA Replicates A Semi Conservative replication each new double helix has one daughter strand one parental strand B Starts at sites called origins C Bacteria have 1 small circular chromosome with one origin III Replication fork Diagram A Bidirectional replication 1 Replication occurs in both directions from the origin B Each new strand 1 Has the opposite orientation from the parent strand 2 Forms in its 5 3 direction a DNA polymerase can only move from 5 3 on daughter strand C At each origin the lagging strand is built in one piece the lagging strand is built in pieces Fig 12 5 IV DNA Replication Fig 12 5 A General 1 Leading Strand Parent strand that is unzipped in its 3 5 direction 2 Lagging Strand Other parent strand that is unzipped in its 5 3 direction 3 Both daughter strands are synthesized in the 5 3 direction a For the leading strand that doesn t cause a problem b For lagging strand DNA is replicated in fragments 4 Happens during S phase of cell cycle B Enzymes Proteins Functions 1 DNA Polymerase creates elongates daughter DNA a Also proofreads new DNA to make sure there are no mistakes in it 2 DNA Helicase 3 RNA Primase 4 Single Stranded Binding Proteins 5 DNA Topoisomerase 6 DNA Ligase unzips existing DNA adds a small RNA sequence to unzipped DNA primer glues together Okazaki fragments on lagging strand relieves stress on DNA during unzipping prevent unzipped DNA from coming back together C Process 1 DNA Helicase hydrolyzes ATP to unwind the existing double helix a As it unwinds the replication bubble forms i In that bubble both single strands of existing DNA are replicated by DNA polymerase see diagram b Single stranded binding proteins prevent separated parent strands from coming back c DNA topoisomerase relieves the stress of uncoiling ahead of the replication fork so DNA together doesn t break In the bubble DNA polymerase elongates the existing strands starting at their 5 ends 2 3 To start adding nucleotides DNA polymerase needs a starting sequence a To make DNA polymerase start working RNA primase makes a short strand of RNA primer b DNA polymerase extends the primer i On the lagging strand DNA polymerase will run into the primer of the preceding fragment A different form of DNA polymerase replaces these primers with DNA 4 On the lagging strand DNA ligase anneals Okazaki fragments V Lots of Equipment is involved fig 12 8 Process reiterated A Red piece is the starting piece of the light blue strand starting strand 1 You get this from RNA primase a Makes a short strand of RNA called a primer DNA polymerase extends the primer Fig 12 6 12 5 3 Okazaki fragment B On the lagging strand DNA polymerase will run into the primer of the preceding fragment Fig a When that happens a different DNA polymerase from removes the primer and fills in the DNA fig 12 6 3 C DNA ligase joins the DNA fragments Fig 12 6 VI Summary A RNA primase makes primers B One type of DNA polymerase extends strand C MAKE ENZYME FUNCTION LIST FOR THIS CHAPTER D A 23nd type of DNA poly removes any primers fills in DNA E DNA ligase bonds any fragments VII Most types of DNA polymerase can proofread A Checks that the most recently added nucleotide is correct if not it will cut it out and add the correct one fig 12 7 Replication Fork where parental strands separate Replication Fork 3 5 Formation of daughter strand Origin of Replication Formation of daughter strand 5 3 Replication Bubble
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