1. DNA Replication Lesson 2

2. Label the ends of DNA strand as either 5’ or 3’. 5’

3. Leading Strand 5’ 3’ helicase SSBPs gyrase primase 5’ 3’ DNA polymerase III The leading strand is synthesized continuously during DNA replication

4. Lagging Strand Okazaki fragment 5’ 3’ 5’ 3’ The laggin strand is synthesized discontinuously during DNAreplication

5. Connecting Lagging Strands DNA polymerase I – removes the RNA primer DNA ligase – connects the sugar- phosphate backbone of Okazaki fragments

6. Mistakes in DNA Replication less than 1 error in 10 7 (10 million) NTs exonuclease – enzymes which can cut out sections of the DNA strand DNA polymerase I and III and exonuclease work together to fix mistakes Nuclease DNA polymerase DNA ligase A distorted section of DNA. 1 A nuclease enzyme cuts the damaged DNA strand at two points and the damaged section is removed. 2 Repair synthesis by a DNA polymerase fills in the missing nucleotides. 3 DNA ligase seals the Free end of the new DNA To the old DNA, making the strand complete. 4

7. Replicating the Ends of DNA Molecules The ends of eukaryotic chromosomal DNA –Get shorter with each round of replication Figure 16.18 End of parental DNA strands Leading strand Lagging strand Last fragmentPrevious fragment RNA primer Lagging strand Removal of primers and replacement with DNA where a 3 end is available Primer removed but cannot be replaced with DNA because no 3 end available for DNA polymerase Second round of replication New leading strand New lagging strand 5 Further rounds of replication Shorter and shorter daughter molecules 5 3 5 3 5 3 5 3 3

8. Eukaryotic chromosomals –Have repeated short nucleotide sequences, called telomeres at their ends that do not code for amino acids. –postpone the erosion of genes near the ends of DNA molecules (e.g. in humans  100-1,000 TTAGGG) Figure 16.19 1 µm

9. Some cells (like cervical cancer cells) have an enzyme called telomerase –Lengthens the telomeres, thus restoring original length and compensating for shortening that occurs during DNA replication. –Contributes to the “indestructible” nature of cancer cells

10. Explain the function of each of the following enzymes in DNA replication: DNA gryase Relieves the tension produced by the unwinding DNA during replication DNA helicase Unwinds the DNA double helix by disrupting hydrogen bonds between base pairs DNA polymerase I Removes RNA primers and replaces them with the appropriate deoxyribonucleotides (DNA bases) during DNA replication DNA polymerase III Makes complementary strands of DNA (adds deoxyribonucleoside triphosphates to the 3’ end of the elongating strand DNA ligase Joins DNA fragments together by catalyzing the formation of a bond between the 3’ hydroxyl group and a 5’ phosphate group on the sugar-phosphate backbones RNA primaseMakes RNA primers

11. Review from previous lessons –Pg. 198 Section Review - #2, 3, 7 (info from previous lessons) Material from today’s lesson –Pg. 204 Section Review - #2 –Pg. 205 Understanding Concepts - #8, 9, 10, 15, 18, 25, 33, 42