Thorns are modified branches, as in citrus and acacia; spines

are modified leaves

Prickles are derived mainly from the epidermis and thus can be easily snapped off the stem, protect plants from larger herbivores

Trichomes, or hairs, provide a much more effective defense against insect pests

TLS Online TPP Program

#Id: 6413

#Unit 2. Cellular Organization

on attenuation for their control. In the case of the leucine operon, its leader peptide has four adjacent leucine codons, and the histidine operon leader peptide has seven histidine codons in a row.

TLS Online TPP Program

#Id: 6414

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 6415

#Unit 2. Cellular Organization

RNA Polymerase don’t get dissociated with one hairpin which is 2:3

TLS Online TPP Program

#Id: 6416

#Unit 2. Cellular Organization

Transcription is initiated at the beginning of the 162 nucleotide mRNA leader encoded by a DNA region called trpL

TLS Online TPP Program

#Id: 6417

#Unit 2. Cellular Organization

The trp operon is controlled by repression and attenuation, providing a two-stage response to progressively more stringent tryptophan starvation. But attenuation alone can provide robust regulation: other amino acid operons such as leu and his rely entirely on attenuation for their control. In the case of the leucine operon, its leader peptide has four adjacent leucine codons, and the histidine operon leader peptide has seven histidine codons in a row.

TLS Online TPP Program

#Id: 6418

#Unit 2. Cellular Organization

The promoter of the araBAD operon from E. coli is activated in the presence of arabinose and the absence of glucose and directs expression of genes encoding enzymes required for arabinose metabolism. 

Unlike the cases of lac and gal genes, where a repressor and an activator work together, here two activators work together: AraC and CAP.