BCHM-3050 Lecture Notes - Lecture 5: Phosphodiester Bond, Sv40, Helicase
23 May 2018
School
Department
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Professor
Subunit Structure of Polymerase III
Holoenzyme: collection of protein subunits with varying functions
Remember: bacterial polymerase's are multimers
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Core of polymerase III: alpha, epsilon and theta subunits
Alpha subunit: polymerase activity
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Epsilon subunit: 3' => 5' exonuclease activity
Reverse proofreading
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Theta subunit: assists epsilon subunit
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Beta subunit: helps keep DNA polymerase bound to template during
nucleotide unwinding
Operates like a clamp
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Helicase mediated DNA unwinding
Helicase: unwind double stranded DNA
Creates fork
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Topoisomerase: keep DNA from over winding
Relieve torsional stress
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Topoisomerase
Topoisomerase: relieve stress by nicking one strand of DNA by forming
covalent phosphodiester bond to 5' phosphate
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NEED TO KNOW FOR EXAM
FUNCTION
E.COLI
HUMAN
DNA polymerase
Pol III
Pol delta, pol epsilon
Primase
DNA G
Pol alpha
Helicase
DNA B
Sv40 T antigen
Proofreading
Epsilon subunit
Pol delta
RNA primer removal
Pol I RNAse
Pol delta, Fen 1
Completion of synthesis of 5' end of linear chromosome
Eukaryotes: need to be able to detach DNA from histone
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Excision of RNA primer = gap that cant be filled
No 3' primer to extend
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Start to lose DNA if the gaps are not filled
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Solution: use telomeres
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Extension of Telomeric DNA via telomerase
Telomere: tandem repeat sequence located at end of chromosomes
Prevent loss of coding sequence
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G quadruplex
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DNA proofreading removes mismatched nucleotides
Polymerase accuracy determined at nucleotide insertion step and reverse
proofreading step
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Mismatch increases Km by 1k fold
Huge increases and will decrease binding
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Reduce speed of extension which allows unwinding into
exonuclease site
So mismatch can be removed
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Also. dNTP pool imbalance can lead to replication error
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Chapter 22: Proteins of Replication
Wednesday, May 23, 2018
1:00 PM
