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Sunday, 25 November 2007

genetic engineering (4)

DNA replication
semiconservative
1.helix-destabilizing protein-helicase
2.single strand DNA binding protein (SBP, DBP)
3. DNA gyrase or topoisomerase-replication fork
4.primase-synthesize small RNA primer
5.DNA polymerase
E coli- pol3 leading strand 5'-->3', lagging strand small fragment (Ogazaki fragment), pol I 5'->3' exonuclease)
polI (C-terminal -polymerase, 3'-5' exonuclease -Klenov fragment, short N-terminal, 5'-3' exonuclease) -proofreading
Mammals-alpha-nuclear-polymerase, beta-nuclear-repair, delta -nuclear similar alpha, gamma-mitochondria-mitochondrial DNAreplication
6. DNA ligase
bidirectional
E coli- 1 replicon
Yeast-500 replicon
Drosophila-3500 replicon
Toad-15000 replicon
Mice 25000 replicon
plant -35000 replicon

Model
1. Theta model-circular DNA-bacteria, mitochondria
2. Sigma model-rolling circle model: phage lambda circular dsDNA-nick, unwheel, produce linear DNA-concatamer, catenated DNA, phage M13 circular ssDNA --> circular dsDNA--> linear ssDNA-->circular ssDNA
3. Y-shaped model-phage T7 linear dsDNA, higher organisms- chromosome

telomerase - terminal deoxynucleotidyltransferase - repeat CCCTAA---> inverted to complementary
found in egg and sperm only
so shorten of chromosome each replication 50-60 times --.senescence

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