Initiation of replication at oriC starts with formation of a complex that ultimately requires six proteins: DnaA, DnaB, DnaC, HU, gyrase, and SSB.

TLS Online TPP Program

#Id: 1380

#Unit 4. Cell Communication and Cell Signaling

The critical concentration (Cc) is the concentration of free G-actin at which the filaments are formed.

TLS Online TPP Program

#Id: 1381

#Unit 4. Cell Communication and Cell Signaling

At steady state, ATP–G-actin subunits add preferentially to the (+) end, while ADP–G-actin subunits disassemble from the (−) end, giving rise to treadmilling of subunits.

TLS Online TPP Program

#Id: 1382

#Unit 4. Cell Communication and Cell Signaling

Profilin enhances the exchange of ADP for ATP on G-actin. Cofilin enhances the rate of loss of ADP-actin from the filament (−) end. Thymosin-β4, binds to ATP–G-actin in such a way that it inhibits addition of the actin subunit to either end of the filament.

TLS Online TPP Program

#Id: 1383

#Unit 4. Cell Communication and Cell Signaling

Formin protein nucleate the assembly of unbranched filaments, (FH1 and FH2 domains-Actin nucleation by the formin FH2 domain).

Formins are activated by membrane-bound Rho-GTP, a Ras-related small GTPase.

The Arp2/3 Complex Nucleates Branched Filament Assembly.

TLS Online TPP Program

#Id: 1384

#Unit 4. Cell Communication and Cell Signaling

Toxins affect the dynamics of actin polymerization; some, 

Latrunculin

Phalloidin

Cytochalasin D

Jasplakinolide

TLS Online TPP Program

#Id: 1385

#Unit 4. Cell Communication and Cell Signaling

There are three classes of myosins, are present in many eukaryotes: 

Myosin I- single head domain

Myosin II- two heads and assembles into bipolar filaments

Myosin V- two heads but does not assemble into filaments