Parasites can be classified

Microparasites

Macroparasites

Ectoparasites

Endoparasites

TLS Online TPP Program

#Id: 6302

#Unit 3. Fundamental Processes

During abortive Transcription, RNA Polymerase Remains Stationary and Pulls Downstream DNA into Itself RNA polymerase produces and releases short RNA transcripts of 10 nucleotides (abortive synthesis) before escaping the promoter, 

 

During abortive Transcription, RNA Polymerase Remains Stationary and Pulls Downstream DNA into Itself

RNA polymerase produces and releases short RNA transcripts of 10 nucleotides (abortive synthesis) before escaping the promoter, entering the elongation phase, and synthesizing the proper transcript. It has long been unclear how the enzyme’s active site translocates along the DNA template during initial abortive cycles of transcription. Three general models were proposed:- “transient excursion”, “Inchworming”, “Scrunching”

 

TLS Online TPP Program

#Id: 6303

#Unit 3. Fundamental Processes

RNA polymerase can initiate a new RNA chain de novo on a DNA template and thus does not need a primer

TLS Online TPP Program

#Id: 6304

#Unit 3. Fundamental Processes

Breaking and remaking bonds in the process of the nucleotide addition cycle and undergoing translocation by a Brownian ratchet mechanism.Indeed, rrn  transcription is insensitive to iNTP and ppGpp in mutants lacking DskA.

TLS Online TPP Program

#Id: 6305

#Unit 3. Fundamental Processes

The E. coli rrn promoters are also regulated by a pair of small molecules: the initiating NTP (the iNTP) and an alarmone,  guanosine 5 -diphosphate 3-diphosphate (ppGpp). An abundance of iNTP indicates that the concentration of  nucleotides is high, and therefore it is appropriate to synthesize plenty of rRNA. 

TLS Online TPP Program

#Id: 6306

#Unit 3. Fundamental Processes

Accordingly, iNTP stabilizes the open promoter complex, stimulating transcription. On the other hand, when cells are starved for amino acids, protein synthesis cannot occur readily and the need for ribosomes (and rRNA) decreases. Ribosomes sense the lack of amino acids when uncharged tRNAs bind to the ribosomal site where aminoacyl-tRNAs would normally bind. 

TLS Online TPP Program

#Id: 6307

#Unit 3. Fundamental Processes

Under these conditions, a ribosome-associated protein called RelA receives the “alarm” and produces the “alarmone” ppGpp, which destabilizes open promoter complexes whose lifetimes are normally short, thus inhibiting Transcription. 

The protein DskA binds to RNA polymerase and reduces the lifetimes of the rrn open promoters to a level at which they are responsive to changes in iNTP and ppGpp concentrations. Thus, DskA is required for the regulation of rrn  transcription by these two small molecules.