The axis of the primitive streak is equivalent to the dorsal-ventral axis of amphibians.

TLS Online TPP Program

#Id: 2298

#Unit 3. Fundamental Processes

The transition from the closed to the open complex involves structural changes in the enzyme and the opening of the DNA double helix to reveal the template and nontemplate strands. This “melting” occurs between positions –11 and +2, with respect to the transcription start site.

TLS Online TPP Program

#Id: 2299

#Unit 3. Fundamental Processes

By 1969 SDS-PAGE of RNA polymerase from E. coli had shown several subunits

1.2 very large subunits are b (150 kD) and b’ (160 kD)

2. Sigma (s) at 70 kD

3. Alpha (a) at 40 kD – 2 copies present in holoenzyme

4. Omega (w) at 10 kD 

TLS Online TPP Program

#Id: 2300

#Unit 3. Fundamental Processes

The overall reaction rate for the bacterial RNA polymerase can be as fast as 40–50 nucleotides/ second at 37°C for most transcripts

TLS Online TPP Program

#Id: 2301

#Unit 3. Fundamental Processes

The overall reaction rate for the bacterial RNA polymerase can be as fast as 40–50 nucleotides/ second at 37°C for most transcripts; this is about the same as the rate of translation (15 amino acids/sec), but much slower than the rate of DNA replication (800 bp/sec).

TLS Online TPP Program

#Id: 2302

#Unit 3. Fundamental Processes

As RNA polymerase moves along the DNA template, it unwinds the duplex at the front of the bubble (the unwinding point), and the DNA automatically reforms the double helix at the back (the rewinding point). 

1. The length of the transcription bubble is 12 to 14 bp, but the length of the RNA–DNA hybrid within the bubble is only 8 to 9 bp. 

2. As the enzyme moves along the template, the DNA duplex reforms, and the RNA is displaced as a free polynucleotide chain. 

3. The last 14 ribonucleotides in the growing RNA are complexed with the DNA and/or the enzyme at any given moment.

TLS Online TPP Program

#Id: 2303

#Unit 3. Fundamental Processes

Mechanism: How Polymerase Find Promoter Sequences