Unit 4 part 6: Viruses: replication and effects of viral infections Flashcards
viral replication strategies can depend on what 4 thiings
their viral genomic nucleic acids
capsid
envelope
symmetry
what are the 6 major steps in a viral replication cycle
attachment aka adsorption penetration uncoating biosynthesis assembly release
what happens in the uncoating phase
capsid is made protein coat and the virus removes the protein coat and injects nucleic acid into the cell
what happens during biosyntheis
virus hijacks the inside machinery to make their own copies, host cell is hijaked by the virus
what happens during assembly
need to be assembled into the virus
how do naked viruses attach
through interactions between their capsid proteins and the host cell membrane receptors
how does the rhinovirus attach to a host cell since it is a naked virus
intracellular adhesions between the molecule ICAM-1 which is involved in the inflammatory and immune response
virus uses ICAM-1 as a key to get into the cell
rhinovirus binds to ICAM-1 receptors
what virus is responsible for 50% of common cold cases
rhinovirus
what can prevent the rhinovirus from attaching to ICAM-1
antibodies can bind to the surface of the rhinovirus
how do enveloped viruses attach to the host cell
use glycoprotein spikes allow the viurs to attach to the host cell surface receptors
how does HIV attach in humans
glycoprotien spikes (gp 120) on HIV attaches to CCR5 (co-receptors) on T helper cells in humans
what is CCR5 also known as
CD195
what is What kind of receptor is CCR5
chemokine - direct traffic to cellular infection so leukocytes know where the infection is
if someone lacks what receptor they are immune to HIV
CCR5
- but cannot able to direct leukocytes
what are two ways a virus can penetrate a cell
fusion between the viral envelope and the host cell membrane
endocytosis (receptor mediated) or engulfment into a vesicle
what occurs in the uncoating process
release of viral nucleic acid (from the protein coat, i.e. capsid) inside the cell
what occurs in the biosynthesis stage
synthesis of new viral nucleic acids and proteins (lots of variations!)
replication of viral genome
mRNA synthesis (transcription)
production of viral proteins (e.g. capsomers)
what do the events of biosynthesis to a varying degree depend upon
certain host-derived & virus-specific replication enzymes
what is one of the most important active and important steps in viral replication
biosynthesis
how many copies of a virus can an infected cell create in a single cycle
tens of thosands
what occurs during the viral assembly stage
newly synthesized viral genome and other components (e.g. enzymes) are incorperated into the capsid forming the nucleocapsid
the new virons from naked viruses in the assembly stage are said to be what?
mature (i.e they are complete and infectious)
- non naked viruses are not complete as they have to grab their coat on the way out
what is the final step in the viral replication cycle
release of mature viruses
how are naked viruses released
mature viruses accumulate in the cell eventually leading to cell death and are released by cell lysis (lytic infection)
how are eneveloped viruses released
nucelocapsid “buds” through the cell membrane
picks up phospholipids to produce a mature virus with the envelope (budding/exocytosis)
what leads to showing S & S in a viral infection
immune system recognizes abnormal cells
cells are destroyed
tissue damage due to inflammation and immune responses
