The binding of sugar phosphates, such as ribulose-1,5-bisphosphate, to rubisco prevents carbamylation. The sugar phosphates can be removed by the enzyme rubisco activase, in a reaction that requires ATP. The primary role of rubisco activase is to accelerate the release of bound sugar phosphates, thus preparing rubisco for carbamylation

TLS Online TPP Program

#Id: 6026

#Unit 3. Fundamental Processes

Pol a/primase enzyme binds to the initiation complex at the origin and synthesizes a short strand consisting of 10 bases of RNA followed by 20 to 30 bases of DNA called as iDNA. 

It is then replaced by an enzyme that will extend the chain.  On the leading strand, this is DNA polymerase E; on the lagging strand this is DNA polymerase d. This event is called the polymerase switch.

TLS Online TPP Program

#Id: 6027

#Unit 3. Fundamental Processes

DNA polymerase E is a highly processive enzyme that continuously synthesizes the leading strand. Its processivity results from its interaction with RFC clamp loader and trimeric PCNA processivity clamp

TLS Online TPP Program

#Id: 6028

#Unit 3. Fundamental Processes

RFC is a clamp loader that catalyzes the loading of PCNA onto DNA. It binds to the 3’ end of the DNA and uses ATP hydrolysis to open the ring of PCNA so that it can encircle the DNA.

TLS Online TPP Program

#Id: 6029

#Unit 3. Fundamental Processes

The crystal structure of PCNA closely resembles the E. coli b subunit: A trimer forms a ring that surrounds the DNA.  The sequence and subunit organization are different from the dimeric b2 clamp; however, the function is likely to be similar.

TLS Online TPP Program

#Id: 6030

#Unit 3. Fundamental Processes

The exonuclease FEN1 removes the RNA primers of Okazaki fragments. The complex of DNA polymerase d and FEN1 carries out the same type of nick translation that E. coli DNA polymerase I carries out during Okazaki fragment maturation

TLS Online TPP Program

#Id: 6031

#Unit 3. Fundamental Processes

In mammalian systems where the DNA polymerase does not have a 5’–3’ exonuclease activity, Okazaki fragments are connected by a two-step process.