Flow cytometry or FACS is the sine qua non (without which, nothing) of the modern immunologist’s toolbox.

Flow cytometry is based on light scattering and fluorescence 

Forward light scattering detect shape and side scattering detects granularity and complexity of the cell

TLS Online TPP Program

#Id: 612

#Unit 2. Cellular Organization

Repression-Trp aporepressor dimer binds high tryptophan, changes conformation with high affinity for trp operator Tryptophan is a corepressor

 

TLS Online TPP Program

#Id: 613

#Unit 2. Cellular Organization

trp operon can run even in the presence of repressor. The attenuation system permits another 10-fold control over the operon’s activity. 

Thus, the combination of repression and attenuation controls the operon over a 700-fold range, from fully inactive to fully active: (70-fold [repression] X 10-fold [attenuation] = 700-fold). 

TLS Online TPP Program

#Id: 614

#Unit 2. Cellular Organization

Attenuation is primarily based on riboswitch (Leader sequence) that function in co-translationally in trp operon

TLS Online TPP Program

#Id: 615

#Unit 2. Cellular Organization

Attenuator riboswitch (Leader sequence) is made up of almost 140 nt which further can be divided into four Intra -complementary regions 

TLS Online TPP Program

#Id: 616

#Unit 2. Cellular Organization

Attenuator riboswitch (Leader sequence) contains two major check-points in region 1

1. UGG codons on position 10, 11

2. A stop codon UGA between Region 1 and 2

TLS Online TPP Program

#Id: 617

#Unit 2. Cellular Organization

Attenuator riboswitch (Leader sequence) region 1 is translated atleast till codon 10 and 11 in case of Low trp concentration.