The plasma proteins are also responsible for 15% of the buffering capacity of the blood because of the weak ionization of their substituent COOH and NH2 groups.

TLS Online TPP Program

#Id: 5892

#Unit 3. Fundamental Processes

DNA polymerases fall into five families based on sequence homologies; the palm is well conserved among them, but the thumb and fingers provide analogous secondary structure elements from different sequences.

TLS Online TPP Program

#Id: 5893

#Unit 3. Fundamental Processes

base pairs at the 3’ end of the primer, which are in the more open A-form. A sharp turn in the DNA exposes the template base to the incoming nucleotide

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.