The precursor RNA for the siRNA pathway is a longer dsRNA. As a consequence of this different initial substrate, Drosha is not needed for the generation of siRNAs. Cleavage by Dicer is still required, however, and again generates a suitable 21- to 22-nucleotide RNA for incorporation into RISC.

TLS Online TPP Program

#Id: 9931

#Unit 4. Cell Communication and Cell Signaling

Original antigenic sin

Tendency to focus an immune attack on those structures that were present during the original.

This means that our immune systems effectively ignore the subtle changes occurring each year in pathogens

TLS Online TPP Program

#Id: 9932

#Unit 4. Cell Communication and Cell Signaling

TLS Online TPP Program

#Id: 9933

#Unit 4. Cell Communication and Cell Signaling

Bacterial Infections

Bacteria enter the body through several natural routes.

TLS Online TPP Program

#Id: 9934

#Unit 4. Cell Communication and Cell Signaling

Cell wall endotoxins of some gram-negative bacteria activate macrophages, resulting in release of high levels of IL-1 and TNF-α, which can cause septic shock.

TLS Online TPP Program

#Id: 9935

#Unit 4. Cell Communication and Cell Signaling

In staphylococcal food poisoning and toxic shock syndrome, exotoxins produced by the pathogens function as superantigens, which can activate all T cells. 

TLS Online TPP Program

#Id: 9936

#Unit 4. Cell Communication and Cell Signaling

Extracellular Bacteria