From the four possible transitions (n!p*, p!p*, n!s*, s!s*), only two can be elicited with light from the UV/Vis spectrum for some biological molecules: n!p* and p!p*. The n!s* and s!s* transitions are

energetically not within the range of UV/Vis spectroscopy and require higher energies.

TLS Online TPP Program

#Id: 6364

#Unit 2. Cellular Organization

Effects of mutations in the three lac operators All three operators are essential for effective repression.

TLS Online TPP Program

#Id: 6365

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 6366

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 6367

#Unit 2. Cellular Organization

This 21-bp sequence is twofold symmetric and is recognized by two subunits of Lac repressor, one binding to each half-site

TLS Online TPP Program

#Id: 6368

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 6369

#Unit 2. Cellular Organization

When polymerase binding causes transition to the open complex and initiates transcription. This gives a low level of constitutive expression called the basal level.  Binding of RNA polymerase is the rate-limiting step in this case.