07BIS1012013ReplicLect_7

Dna

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Unformatted text preview: NA) can only be polymerized in the 5' to 3' direction. 2. The ends of a double stranded DNA molecule must be anti-parallel. 3. DNA polymerase can not initiate the polymerization process de novo (a primer is DNA de required). required). 4. Primers must be removed before DNA replication is complete. ­ Components: 1. Deoxyribonucleotide triphosphate precursors (dATP, dTTP, dCTP, dGTP). 2. 3'-OH template primer. 3. DNA polymerases I and III. 4. DNA polymerase 5' to 3' exonuclease activity for primer removal. 5. DNA polymerase 3' to 5' exonuclease activity for correcting errors. 6. RNA polymerase (primase) for RNA primer synthesis. (This enzyme can initiate de novo) RNA de 7. DNA ligase for sealing up nicks in DNA. 8. DNA unwinding enzymes like dnaA, helicas and rep A protein. DNA dnaA 9. Helix destabilizing proteins (ssb). 10. DNA gyrases like topoisomerase II 10. DNA ­ BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 40 Comparison of DNA polymerase I and III Characteristics pol Ia pol III Molecular weight De novo initiation 5’-3’ polymerization Polymerization rateb 3’-5’ exonuclease 5’-3’ exonuclease 103kDal — + ~600bp/min + + 380kDal — + ~6000bp/min + (—) A 67kDal proteolytic cleavage product of pol I (Klenow fragment) possesses the 5’-3’ polyermization activity, but fragment) not the 5’-3’ exonuclease activity. b The E. coli chromosome replicates at a rate E. of 25K to 60K bp/min/fork or ~1000bp/sec/fork. of a BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 41 DNA Polymerase III (p. 243) Monomer α140 kD α140 kD ε25kD δ 32kD γ 52kD ε25kD θ 10kD τ 83kD δ 32kD γ 52kD β 37kD θ 10kD τ 83kD β 37kD Dimer BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 42 Anti parallel sugar-phosphate chains BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 43 The 5’ to 3” Dilemma ­ The 5' to 3' dilemma. Because the newly synthesized strands of DNA Because must be antiparallel to the template strands, and the replication fork moves forward, it would appear that one strand must be synthesized in the 3' to 5' direction. However, no DNA or RNA polymerase with this activity has ever been found in nature. The solution to this dilemma is to synthesize of the one strand backwards, in the 5' to 3' direction. This is referred to as discontinuous synthesis of the lagging strand. The idea discontinuous for discontinuous synthesis was first put forth by Dr. Reiji Okazaki who Okazaki used 3H-thymidine and pulse-chase experiments to show...
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This note was uploaded on 02/12/2014 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

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