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
Movies and Videos
• http://www.youtube.com/watch?v=teV62zrm2P0&feature=related
• http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.html
• http://www.bioteach.ubc.ca/TeachingResources/MolecularBiology/DNAReplication.swf
• http://bcs.whfreeman.com/thelifewire/content/chp11/1102002.html
• http://www.youtube.com/watch?v=4jtmOZaIvS0• http://www.youtube.com/watch?v=dIZpb93NYlw
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