C8 having two peptide chains: C8β and C8αϒ. Binding of C8β with C5b67 complex causes conformational change in the C8 dimer such that hydrophobic domain of C8αϒ can insert into the interior of the phospholipid membrane.

TLS Online TPP Program

#Id: 5894

#Unit 3. Fundamental Processes

When a nucleotide binds, the fingers domain rotates 60° toward the palm, with the tops of the fingers moving by 30 Å. The thumb domain also rotates toward the palm by 8°. 

These changes are cyclical:

They are reversed when the nucleotide is incorporated into the DNA chain, which then translocates through the enzyme to recreate an empty site.

TLS Online TPP Program

#Id: 5895

#Unit 3. Fundamental Processes

The palm domain is composed of a b sheet and contains the primary elements of the catalytic site. In particular, this region of DNA polymerase binds two divalent metal ions.

TLS Online TPP Program

#Id: 5896

#Unit 3. Fundamental Processes

One metal ion reduces the affinity of the 3’-OH for its hydrogen. This generates a 3’O- that is primed for the nucleophilic attack of the a-phosphate of the incoming dNTP. 

TLS Online TPP Program

#Id: 5897

#Unit 3. Fundamental Processes

The second metal ion coordinates the negative charges of the b-phosphate and g phosphate of the dNTP and stabilizes the pyrophosphate produced by joining the primer and the incoming nucleotide.

TLS Online TPP Program

#Id: 5898

#Unit 3. Fundamental Processes

The average number of nucleotides added before a polymerase dissociates defines its processivity. Nucleotides added per unit time dissociates defines its polymerisation

The 3’->5’ exonuclease activity removes the mispaired nucleotide, and the polymerase begins again known as proofreading

TLS Online TPP Program

#Id: 5899

#Unit 3. Fundamental Processes