©2001 Timothy G. Standish Jeremiah 10:12 12He hath made the earth by his power, he hath established the world by his wisdom, and hath stretched out the

©2001 Timothy G. Standish

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.


RepliconsRepliconsTimothy G. Standish, Ph. D.


The Information Catch-22The 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


The Cell LifecycleThe 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


G1G1

MM

G2G2

SS

The Cell LifecycleThe Cell LifecycleGap 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

Gap 2 - Final preparation for division

Mitosis - Cell division


Stages of ReplicationStages 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


InitiationInitiation 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


Initiation - Forming the Initiation - Forming the Replication Eye Or BubbleReplication Eye Or Bubble

3’ 5’

3’5’5’

5’

3’

3’

Origin of Replication

5’

3’

3’

5’

5’3’

5’

5’

5’

3’

3’3’

Replication eye orreplication bubble


Large Linear Chromosomes Have Large Linear Chromosomes Have Many Origins Of ReplicationMany Origins Of Replication

5’3’

3’5’

5’3’

3’5’

3’5’

5’3’

3’5’

5’3’

3’5’

5’3’

Origins of Replication


Cell Wall

Cytoplasm

Cell Membrane

Bacteria Have Circular Bacteria Have Circular ChromosomesChromosomes

Termination ofReplication

Origin ofReplicationChromosome


ReplicationReplication

End of replicationTwo chromosomes

OriginalChromosome

Start of replicationTheta () structure

Replication goes in both directions

Mid replication


Binary Fission RevisitedBinary Fission Revisited


Various Replication StrategiesVarious Replication Strategies D-loop Rolling circle


F- bacteria

2 Conjugation2 ConjugationF plasmid

Mating Bridge

F+ bacteria

Fplasmid


2 Conjugation2 Conjugation

F- bacteria

F plasmid

F+ bacteria

Fplasmid

Mating Bridge



F- bacteria

F plasmid

F+ bacteria

Fplasmid

Mating Bridge



F- bacteria

F plasmid

F+ bacteria

Fplasmid

Mating Bridge



F- bacteria

F plasmid

F+ bacteria

Fplasmid

Fplasmid

Mating Bridge


Transfer of genetic material

Hfr RecombinationHfr Recombination

F+ bacteria

F- bacteria

F plasmid Integration

Hfr cell



F+ bacteria

F- bacteria

Crossing over Transfer of genetic material

Interruption of conjugation

Hfr cellF plasmid Integration



F+ bacteria Hfr cellF plasmid Integration

F- bacteria

RecombinantBacteria


Documents

©2001 Timothy G. Standish Jeremiah 10:12 12He hath made the earth by his power, he hath established the world by his wisdom, and hath stretched out the