M6P residues are generated in the cis-Golgi by two Golgi-resident enzymes. 

1. N-acetylglucosamine (GlcNAc) phosphotransferase
2. Phosphodiesterase

TLS Online TPP Program

#Id: 1510

#Unit 2. Cellular Organization

A microtubule is a hollow cylindrical structure built from 13 parallel protofilaments, each composed of αβ-tubulin heterodimers stacked head to tail and folded into a tube.

TLS Online TPP Program

#Id: 1511

#Unit 2. Cellular Organization

Tubulin dimers in which the β-subunit has bound GTP are added preferentially to (+) end of the microtubule.

TLS Online TPP Program

#Id: 1512

#Unit 2. Cellular Organization

In a microtubule,

The end with exposed β-subunits is the (+) end

The end with exposed α-subunits is the (−) end

 

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.