The second half of the distal tubule and the subsequent cortical collecting tubule have two distinct cell types:  principal cells and intercalated cells

TLS Online TPP Program

#Id: 2292

#Unit 3. Fundamental Processes

Isomerization is essentially irreversible and once complete, typically guarantees that transcription will subsequently initiate .

TLS Online TPP Program

#Id: 2293

#Unit 3. Fundamental Processes

Formation of the closed complex, in contrast, is readily reversible: polymerase can as easily dissociate from the promoter as make the transition to the open complex.

TLS Online TPP Program

#Id: 2294

#Unit 3. Fundamental Processes

During initial transcription, the polymerase remains stationary on the promoter, unwinds downstream DNA, and pulls that DNA into itself

TLS Online TPP Program

#Id: 2295

#Unit 3. Fundamental Processes

scrunching model -proposes that DNA downstream from the stationary, promoter-bound, polymerase is unwound and pulled into the enzyme. The DNA thus accumulated within the enzyme is accommodated as single-stranded bulges.

TLS Online TPP Program

#Id: 2296

#Unit 3. Fundamental Processes

Three general models were proposedfor abortive transcription.

TLS Online TPP Program

#Id: 2297

#Unit 3. Fundamental Processes

Two bases in the non-template strand of the –10 element (A11 and T7) flip out from their base-stacking interactions and instead insert into pockets within the s protein where they make more favorable interactions