Chapter 16 DNA Replication. Base Pairing A forms 2 H bonds with T G forms 3 H bonds with G In RNA, A...

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