Chapter 16 DNA Replication

Base Pairing A forms 2 H bonds with T G forms 3 H bonds with G In RNA, A forms 2 H bonds with U Complimentary strands Anti-parallel orientation

Proteins Involved in DNA Replication Helicase Topoisomerase Single stranded binding proteins Primase DNA Polymerase III DNA Polymerase I DNA Ligase

Steps in DNA Replication Open the strands to access the nitrogenous bases Prime Build leading strand Build lagging strand Repair Open next segment

Opening the DNA Origins of replication Helicase Replication fork Replication bubble Antiparallel alignment Single stranded binding proteins Topoisomerases

Formation of Replication Fork

Priming DNA Replication Primase RNA primer Free 3’ hydroxyl 5’-3’ progression of newly manufactured strand Template strand in 3’- 5’ direction

Building DNA DNA Polymerase III –5’-3’ new strand –3’-5’ template strand Leading strand –Toward replication fork –continuous Lagging strand –Away from replication fork –discontinuous –Okazaki fragments

Clean up DNA Polymerase I –Removes RNA primer –Fills in gap DNA Ligase –Closes nicked region

Summary

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Replicating the Ends of DNA Molecules Chromosome ends Repetitive sequences Shorten with each replicative cycle Fray Time keeper 50 cycles

DNA Organization Histone proteins Nucleosomes Chromosomes Condensed only for cell division