In the case of the bacterial enzyme bearing s70, this transition, often called isomerization, does not require energy derived from ATP hydrolysis and is instead the result of a spontaneous conformational change in the DNA– enzyme complex to a more energetically favorable form.

TLS Online TPP Program

#Id: 9301

#Unit 4. Cell Communication and Cell Signaling

TLS Online TPP Program

#Id: 9302

#Unit 4. Cell Communication and Cell Signaling

11-cis-retinal covalently attached to the amino group of lysine residue 296 in the opsin protein

TLS Online TPP Program

#Id: 9303

#Unit 4. Cell Communication and Cell Signaling

The heterotrimeric G protein coupled to rhodopsin, called transducin (Gt)

TLS Online TPP Program

#Id: 9304

#Unit 4. Cell Communication and Cell Signaling

In the absence of light,  bound 11-cis-retinal locks the rhodopsin into its inactive (R) conformation

TLS Online TPP Program

#Id: 9305

#Unit 4. Cell Communication and Cell Signaling

Absorption of light causes rapid photoisomerization of the bound cis-retinal to the all-trans isomer, triggering a conformational change in opsin that activate the Gαt.

TLS Online TPP Program

#Id: 9306

#Unit 4. Cell Communication and Cell Signaling

There are about 90 million rod cells in the human retina, and each contains about 4x107 molecules of rhodopsin that are very densely packed in the membrane disks.