The SA node exhibits automaticity; it can spontaneously generate action potentials without neural input.

TLS Online TPP Program

#Id: 9925

#Unit 4. Cell Communication and Cell Signaling

Adenoviruses and cytomegalo virus use to reduce the surface expression of class I MHC molecules, 

Measles virus and HIV, reduce levels of class II MHC molecules on the surface, 

Vaccinia virus, secreting a protein that binds to the C4b complement component.

TLS Online TPP Program

#Id: 9926

#Unit 4. Cell Communication and Cell Signaling

Influenza virus

Influenza are surrounded by an outer envelope, a lipid bilayer derived from the plasma membrane of the infected cell.

Viral specific Protein 

Hemagglutinin (HA) 

Neuraminidase (NA)

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#Unit 4. Cell Communication and Cell Signaling

HA trimers are responsible for the attachment of the virus to host cells, binding to the sialic acid. 

NA is an enzyme that cleaves N-acetyl neuraminic (sialic) acid

Within the envelope, consists of eight different strands of single- stranded RNA (ssRNA) associated with protein and RNA polymerase. 

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#Id: 9928

#Unit 4. Cell Communication and Cell Signaling

There are 18 different antigenic subtypes for HA and 11 for NA.

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#Id: 9929

#Unit 4. Cell Communication and Cell Signaling

TLS Online TPP Program

#Id: 9930

#Unit 4. Cell Communication and Cell Signaling

Variation in Influenza Strains

Antigenic variation in HA and NA is generated by

Antigenic drift involves a series of spontaneous point mutations that occur gradually.

Antigenic shift results in the sudden emergence of a new subtype of influenza.