Micro Ch 13

1. DNA or RNA - not both - both can be single or double stranded.

2. Capsid = protective protein coat - made of capsomeres

3. Envelope - not all viruses have it

4. Spikes - some have spikes for attachment to host

Viruses are obligatory intercellular parasite - they cannot reproduce outside of a host cell and thus are not classified as alive.

Virsus are very specific - most often can only infect 1type of cell in 1 species -not always the case (bird flu/ swine flu)

Host Range - spectrum of host cells the virus can infect - this is determined by specific host attachement sites

Most are much smaller than bacteria. They range in size from 30 nm (nanometers) to 1 um (micrometer) - (most bacteria are 1 um in size

• Viral shapes are determined by the capsid
• 1. helical - hollow protein capsule hold DNA or RNA
• 2. polyhedral - icosahedral = 20 sided equilateral triangle faces
• 3. enveloped - only in some - some have spikes on envelope that can mutate (influenza) - roughly spherical
• 4. complex - bacteriophage: head (capsid), body (sheath), legs (fibers)

• A complex virus that affects only bacteria - also called phages
• -on culture plate - they form plaques on a lawn of bacteria

Virion = fully assembled virus

Virsues must be grown in living cells:

• 1. Living animals (living cells of host)
• 2. Embryonated eggs (living cells of host)
• 3. Cell cultures (1 living cell type)

can be used to diagnose viral infections in man - Known viral antigen are mixed with patients serum to detect antibodies against the virus.

• Detection is not always easy becuase most viruses are inside the cell (not in the bloodstream)
• Western blot test is used to confirm HIV infection - looks at serum antibody binding to prepared HIV proteins.

• 1. Attachment - phage attaches by tail fibers to host cell
• 2. Penetration - phage tail releases lysozyme to break open cell wall → sheath contracts → tail core (pin) driven into cell wall → DNA injected into cell (cuspid stays outside)

3. Biosynthesis - of phage DNA and proteins - using host cell machinery

4. Maturation - assembly of phage particles into virions (complete viral particle)

5. Release - phage lysosome lyses cell wall - virus released and cell dies

Lytic cycle - phage replication results in lysis and death of cell

Lysogenic cycle = Prophage (instead of Biosynthesis) - DNA is incorporated in host DNA and then is replicated with each cell division (host cell lives on)

a bacteriophage can do either or both at the same time

Viruses use host cell's machinery to replicate itself

Virus make thousands of itself within 1 cell when it replicates

Host cell either dies (lysis) or lives indefinately to reproduce the virus (HIV integrates itself into host cell genome)

• Penetration - by endocytosis - entire viron enters cell
• Uncoating - of cuspid proteins (by viral or host enzymes)

• 1. Attachement
• 2. Penetration - endocytosis
• 3. Uncoating
• 4. Biosynthesis
• 5. Maturation
• 6. Release - by rupture (lysis) or budding (enveloped virus)

One step growth - virions present in culture until attachment - then no new virons are found in the culture until after biosynthesis and maturation have taken place. Most infected cells die as a result of infection- consequently, new virions will not be produced.

• The eclipse period is the time between infection of the cell and the appearance of the mature virus within the cell.
• 

Provirus - a piece of viral DNA that is integrated into a host cell chromosome - the provirus never comes out of the chromosome- thus it is protected from the host's immune system and antiviral drugs

Prophage - phage DNA inserts itself in the circular bacterial DNA - every time the cell replicates, it replicates the phophage DNA also. Some future even will cause the phage DNA to pop out and initiate the lytic cycle

• HIV = Human Immunodeficiency virus
• 1. HIV virus enters a human T-cell
• 2. uses reverse transcriptase (an enzyme) to copy its RNA into double straded DNA
• 3. DNA then inserts into T-cell DNA -PROVIRUS
• 4. Provirus - always stays inserted - replicates with T-cell division - can turn on at future point and reproduce itself in numbers

RETRo virus - name comes from REverse TRansscriptase

Retrovirus is derived from the name REverse TRanscriptase - the enzyme that

Budding is one method of release of an virus from the host cell (animal only) - The assempled capsid (containing nucleic acid) is pushed through the plasma membrane of the host cell - The plasma membrane adheres to the virus and form the envelope which pinches off the host cell

Oncogenic virus = cancer causing virus

Oncogenes - mutant host cell regulatory genes that can cuase cancer when turned on by a oncogenic virus

all oncogenic viruses integrate themselves into host DNA

a transformed cell is a host cell that is infected by an ongogenic virus and turns into a tumor cell

Latent - virus remians asymptematic for long periods of time - chickenpox/ shingles, herpes 1 (cold sores)

• DNA virus
• veneral warts - cervical cancer

• 100 different HPVs
• - replicate on body surface cells (skin/ mucosa)
• - vaccine

• DNA virus
• Infects the hepatocyte - cell lysis
• Acute Hepititis B viral - usually self-limited

• Chronic active hepititis → cirrhosis of the liver
• can cause hepatoma (cancer)

• Rx - interferon (chronic acive hep)
• Drug induced hepititis

Adenovirus, rhinovirus, coronavirus

• smallpox - DNA
• 30% mortality - to Rx exists -
• can vaccinate up to 3 days after exposure
• pheumonia, encephalitis, corneal ulceration (blindness)

Cowpox = original vaccine (milk maids)

• DNA
• 1. Herpes simplex I - oral
• 2. Herpes simplex II - genital - both inhibit DNA polymerase
• 3. Varicella zoster - chickenpox - lives in sensory neurons
• 4. Kaposi's sarcoma - viral cancer (AIDS dd)
• 5. Epstein-Barr virus - mononucleosis, Burkitt's lymphoma

• RNA
• infects motor neurons - flaccid paralysis

• RNA
• Rubella - german measels
• -fetal abnormalities if mother infected during 1st trimester
• MMR vaccine

• RNA
• rabies -
• death from respiratory failure or acute enchehilitis (travels to brain along peripheral nerves)
• ANY mammel can get it
• 100% mortality once symtomatic
• post exposure vaccination is effective

• RNA virus
• RSV - respiratory syncytial virus - infant bronchoilitis

• Parainfluenza - croup (laryngotracheobronchitis)
• - bronchoilitis

Mumps - infects parotid gland & testes - vaccine

measels - vaccine

• RNA enveloped virus - A, B, C
• antigenic shirt - major change
• antigenic drift - minor change
• spikes mutate often - new vaccine every year

• RNA retrovirus - HIV (Human Immunodeficiency Virus)
• uses its own reverse transcriptase (singel stranded RNA → double stranded DNA)