The start point is usually (90% of the time) a purine. It is common for the start point to be the central base in the sequence CAT, but the conservation of this triplet is not great enough to regard it as an obligatory signal.

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.

TLS Online TPP Program

#Id: 8319

#Unit 2. Cellular Organization

Nucleation phase 

Lag period (Time taken for nucleation) Rate-limiting Step.

TLS Online TPP Program

#Id: 8320

#Unit 2. Cellular Organization

The lag phase can be reduced or abolished entirely by adding premade nuclei.