Electron delocalisation extends throughout the cyclic tetrapyrrole ring of porphyrins and gives rise to an intense transition at 400 nm called the Soret band.

TLS Online TPP Program

#Id: 9701

#Unit 4. Cell Communication and Cell Signaling

Two mating types of yeast cells are: 

1. a 

2. α

TLS Online TPP Program

#Id: 9702

#Unit 4. Cell Communication and Cell Signaling

Haploid yeast cells secrete protein signals known as pheromones, which induce mating between opposite mating types.

TLS Online TPP Program

#Id: 9703

#Unit 4. Cell Communication and Cell Signaling

An a haploid cell secretes the a mating factor and has GPCRs for the α factor on its cell surface; an α cell secretes the α factor and has GPCRs for the a factor.

TLS Online TPP Program

#Id: 9704

#Unit 4. Cell Communication and Cell Signaling

Activation of the MAP kinase pathway by either the a or the α GPCRs induces transcription of genes that inhibit progression of the cell cycle

TLS Online TPP Program

#Id: 9705

#Unit 4. Cell Communication and Cell Signaling

The receptors for yeast α and a mating factors are coupled to the same trimeric G protein.

TLS Online TPP Program

#Id: 9706

#Unit 4. Cell Communication and Cell Signaling

Ligand binding to either of the two yeast pheromone GPCRs triggers the exchange of GTP for GDP on the Gα subunit and dissociation of Gα∙GTP from the Gβγ complex.