Transcript Replicons
Jeremiah 10:12 12 He hath made the earth by his power, he hath established the world by his wisdom, and hath stretched out the heavens by his discretion. ©2001 Timothy G. Standish Replicons Timothy G. Standish, Ph. D. ©2001 Timothy G. Standish The Information Catch-22 “With only poor copying fidelity, a primitive system could carry little genetic information without L [the mutation rate] becoming unbearably large, and how a primitive system could then improve its fidelity and also evolve into a sexual system with crossover beggars the imagination.” Hoyle F. 1987. "Mathematics of Evolution", Acorn Enterprises: Memphis TN, 1999, p 20 ©2001 Timothy G. Standish The Cell Lifecycle The cell lifecycle is well defined and can be divided into four stages: – Gap 1 (G1) - The growth phase in which most cells are found most of the time – Synthesis (S) - During which new DNA is synthesized – Gap 2 (G2) - No transcription or translation occurs and final preparations for division are made – Mitosis - Cell division Once Synthesis is initiated, the cell is committed to division Thus initiation of DNA replication is a carefully controlled process in cells ©2001 Timothy G. Standish The Cell Lifecycle Gap 1 - Doubling of cell size. Regular cellular activities. Transcription and translation etc. Synthesis of DNA Regular cell activities cease and a copy of all nuclear DNA is made S G1 G2 M Gap 2 - Final preparation for division Mitosis - Cell division ©2001 Timothy G. Standish Stages of Replication Replication can be divided into three stages: 1 Initiation - When DNA is initially split into two strands and polymerization of new DNA is started 2 Elongation - When DNA is polymerized 3 Termination - When the new strands of DNA are completed and some finishing touches may be put on the DNA Both elongation and termination may involve proof reading of the DNA ensuring that mutations are not incorporated into newly formed DNA strands ©2001 Timothy G. Standish Initiation Initiation starts at specific DNA sequences called origins (Ori C = origin in E. coli chromosomes) Long linear chromosomes have many origins First the origin melts (splits into two single strands of DNA) Next primers are added Finally DNA polymerase recognizes the primers and starts to polymerize DNA 5’ to 3’ away from the primers ©2001 Timothy G. Standish Initiation - Forming the Replication Eye Or Bubble Origin of Replication 5’ 3’ 3’ 5’ Replication eye or replication bubble 3’ 5’ 5’ 3’ 3’ 5’ 5’ 5’ 3’ 3’ 5’ 3’ 3’ 5’ 5’ 3’ ©2001 Timothy G. Standish Large Linear Chromosomes Have Many Origins Of Replication Origins of Replication 5’ 3’ 3’ 5’ 5’ 3’ 3’ 5’ 5’ 3’ 3’ 5’ 5’ 3’ 3’ 5’ 5’ 3’ 3’ 5’ ©2001 Timothy G. Standish Bacteria Have Circular Chromosomes Cell Wall Cell Membrane Chromosome Origin of Replication Cytoplasm Termination of Replication ©2001 Timothy G. Standish Replication Replication goes in both directions Original Chromosome Start of replication Theta (q) structure Mid replication End of replication Two chromosomes ©2001 Timothy G. Standish Binary Fission Revisited ©2001 Timothy G. Standish Various Replication Strategies D-loop Rolling circle ©2001 Timothy G. Standish F plasmid 2 Conjugation F+ bacteria Mating Bridge F- bacteria F plasmid ©2001 Timothy G. Standish F plasmid 2 Conjugation F+ bacteria Mating Bridge F- bacteria F plasmid ©2001 Timothy G. Standish F plasmid 2 Conjugation F+ bacteria Mating Bridge F- bacteria F plasmid ©2001 Timothy G. Standish F plasmid 2 Conjugation F+ bacteria Mating Bridge F- bacteria F plasmid ©2001 Timothy G. Standish F plasmid 2 Conjugation F+ bacteria Mating Bridge F- bacteria F plasmid F plasmid ©2001 Timothy G. Standish Hfr Recombination F+ bacteria F plasmid Integration Hfr cell F- bacteria Transfer of genetic material ©2001 Timothy G. Standish Hfr Recombination F+ bacteria F plasmid Integration Hfr cell Interruption of conjugation F- bacteria Crossing over Transfer of genetic material ©2001 Timothy G. Standish Hfr Recombination F+ bacteria F plasmid Integration Hfr cell F- bacteria Recombinant Bacteria ©2001 Timothy G. Standish ©2001 Timothy G. Standish