When bound to the ribosome, stringent factor catalyzes formation of the unusual nucleotide guanosine tetraphosphate (ppGpp); it adds pyrophosphate to the 3 position of GTP, in the reaction.

TLS Online TPP Program

#Id: 1462

#Unit 4. Cell Communication and Cell Signaling

The adhesiveness of cadherins depends on the presence of extracellular Ca2+.

TLS Online TPP Program

#Id: 1463

#Unit 4. Cell Communication and Cell Signaling

Two type of Cadherins:

1. Classical cadherin proteins

2. Nonclassical cadherin proteins

TLS Online TPP Program

#Id: 1464

#Unit 4. Cell Communication and Cell Signaling

Each classical cadherin molecule contains: 

A single transmembrane domain

A relatively short C-terminal cytosolic domain

Five extracellular “cadherin” domains (called EC1–EC5)

TLS Online TPP Program

#Id: 1465

#Unit 4. Cell Communication and Cell Signaling

Three classes of classical cadherins: 

E-cadherin -present on many types of epithelial cells

N-cadherin - present on nerve, muscle and lens cells

P-cadherin - present on cells in the placenta & epidermis

TLS Online TPP Program

#Id: 1466

#Unit 4. Cell Communication and Cell Signaling

Nonclassical cadherins include proteins:

• Protocadherins found in the brain

• Desmocollins and desmogleins that form desmosomes

TLS Online TPP Program

#Id: 1467

#Unit 4. Cell Communication and Cell Signaling

Epithelial-to-mesenchymal transition is associated with a reduction in the expression of E-cadherin.