The surfaces of the cells that form the alveoli (small air spaces of the lung) are coated with surfactant, which decreases the alveolar surface tension. 

Lung surfactant contains 80 to 90% phospholipid by weight, and 70 to 80% of the phospholipid is phosphatidylcholine, mostly the dipalmitoyl species.

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.

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