This entails release of DnaC, which allows the DnaB helicase to become active. DnaC hydrolyzes ATP in order to release DnaB. This step marks the transition from initiation to elongation.

TLS Online TPP Program

#Id: 1513

#Unit 2. Cellular Organization

Microtubules exist in three forms:

Singlet

Doublet

Triplet

TLS Online TPP Program

#Id: 1514

#Unit 2. Cellular Organization

Most microtubules in a cell consist of a simple tube, a singlet microtubule, built from 13 protofilaments. 

TLS Online TPP Program

#Id: 1515

#Unit 2. Cellular Organization

Doublet contains one complete 13-protofilament microtubule (A tubule) and one additional tubules (B tubule) consisting of 10 protofilaments.

 

TLS Online TPP Program

#Id: 1516

#Unit 2. Cellular Organization

Triplet contains one complete 13-protofilament microtubule (A tubule) and two additional tubules (B & C tubule) consisting of 10 protofilaments each.

TLS Online TPP Program

#Id: 1517

#Unit 2. Cellular Organization

All microtubules are nucleated from structures known as microtubule-organizing centers, or MTOCs.

 

TLS Online TPP Program

#Id: 1518

#Unit 2. Cellular Organization

In MTOCs, 

The (−) end of the microtubule stays anchored in the MTOC while the (+) end extends away from it.