Transition from CPC to OPC often called isomerization, does not require energy derived from ATP hydrolysis and is instead the result of a spontaneous conformational change in the DNA– enzyme complex to a more energetically favorable form.

TLS Online TPP Program

#Id: 8313

#Unit 2. Cellular Organization

3 isoforms of actin-

α - expressed only in muscle cells

β and γ - found together in almost all non-muscle cells

TLS Online TPP Program

#Id: 8314

#Unit 2. Cellular Organization

Each actin subunit (globular or G-actin) is a 375-amino-acid polypeptide contains a Mg+2 ion complexed with either ATP or ADP

TLS Online TPP Program

#Id: 8315

#Unit 2. Cellular Organization

Actin can reversibly assemble into filaments that consist of two helices of actin subunits

TLS Online TPP Program

#Id: 8316

#Unit 2. Cellular Organization

Persistence length,

minimum filament length at which random thermal fluctuations are likely to cause it to bend.

TLS Online TPP Program

#Id: 8317

#Unit 2. Cellular Organization

Actin polymerization in vitro proceeds in three steps:

1.Nucleation phase

2.Elongation phase

3.Steady-state

TLS Online TPP Program

#Id: 8318

#Unit 2. Cellular Organization

Nucleation phase 

Two G-actin molecules bind relatively weakly to each other, but addition of a third actin monomer to form a trimer makes the entire group more stable, acts as a nucleus for polymerization.