Chapter 6 -- Intro to viruses Flashcards
Roman Empire
Detailed accounts of epidemics
Cortez and the Aztecs
Believe Cortez brought small pox over to Aztecs who had never been exposed
Chamberland
Created porcelain bacterial filter to catch bacterial cells, like a strainer
Dmitri Iwanowski
Tobacco mosaic disease – took filtrate and exposed on healthy plants and they got sick, but still didn’t know why – discovered that viruses are filterable
Martina’s Bejerinck
Credited with coining the term ‘virus’
Wendell Stanley
Visualized viruses
Characteristics of Viruses
Obligate intracellular parasite, particle not a cell, has DNA or RNA, infectious agent, filterable
Density dependence
Or contact inhibition, which is the cells will stop growing if too crowded
Anchorage dependence
Like to grow on a surface
Transformed cells lack
Density and anchorage dependence, which causes tumors and metastasized cells
Oncoviruses
Mammalian viruses capable of initiating tumors
Papilloma virus
All strains cause warts, can cause cervical cancer
Epstein-Barr virus
Mononucleosis, or Burkitt’s lymphoma ( lump, usually on face, mostly in Africa)
Persistent infections
Cell harbors the virus and is not immediately lysed; can last weeks or hosts lifetime
Chronic latent state
Several persistent viruses can periodically reactivate— examples: measles (may remain hidden in brain cells for many years, very rare), herpes simplex virus (cold sores or genital herpes), herpes zoster virus, or varicella ( chickenpox or shingles)
Nucleic acid core
DNA or RNA, linear or circular, carries info to redirect host to make new viruses, may contain enzymes
Capsid
Protein coat of a virus made of amino subunits called capsomeres
Capsomeres
Amino acid subunits in capsid
Nucleocapsid
Genome and capsid together
Spikes
Surface glycoproteins essential for attachment to host receptors on outside of envelope — may cause hemagglutination
Helical
Rod shaped
Polyhedral
Or lcosahedral, many sided
Complex viruses
Atypical viruses
Examples: Pox virus– lacks a typical capsid and covered by dense layer of lipoprotein; Bacteriophage– mean a virus that effects bacteria, polyhedral nucleocapsid head along with a helical “tails” and attachment fibers
-viridae
Family name ends with -viridae, example: Herpesviridae
-virus
Genus name ends with -virus, example: Simplexvirus
Transmission
How to get infected, can be more than One way — example: chicken pox can be transmitted by inhalation or contact
Site of Multiplication
Where it multiplies in cell – animal cell in nucleus and in bacteria in the cytoplasm
General Steps in Viral Replication
- Attachment
- Entry
- Synthesis
- Assembly
- Release
Attachment
Step 1 in replication – binding of virus to specific molecules (receptors) on host cell; contact is random
Entry
Step 2 in replication – virus or genome enters host cell
Assembly
AKA maturation, Step 4 in replication – viral components are assembled
Release
Step 5 in replication – virus leaves the cell to infect other cells; exocytosis
Synthesis
Step 3 in replication – viral components re produced ( DNA or RNA )
Bacteriophage Replication
Lytic cycle or Lysogenic cycle
Lytic cycle
Ends in lysis of cell, essentially the same as general replication
Lysogenic cycle
Host cell gains new properties from incorporated viral genes– host cell gains immunity to reinfection by same virus– prophage is a bacterium with hidden DNA within its DNA
Lysogeny
Spreads virus without killing host cell
Lysogenic conversion
Phage genes in the bacterial chromosome can cause the production of toxins or enzymes that cause pathology
Viral Classification
virus are classified on following criteria: type of host, nucleic acid, morphology, naked or enveloped, transmission ,site of multiplication and symtomology
Steps in Viral Replication
REMEMBER Caesar without the C — Attachment, Entry, Synthesis, Assembly and Release
DNA viruses
generally are replicated and assembled in the nucleus
RNA viruses
generally replicated and assembled in the cytoplasm: Positive-sense RNA contain the message for translation and Negative-sense RNA must be converted into a positive-sense message
Budding
a way a virus leaves a cell – exocytosis; nucleocapsid binds to membrane which pinches off and sheds the virus gradually; cell is not immediatly destroyed
Lysis
one way a virus leaves the host - nonenveloped and complex viruses released when the cell dies and ruptures
Prions
not viruses, but proteins — no nucleic acid, non cellular — can induce spontaneous abnormal folding in normal proteins – extremely resistant to control methods
Satellite viruses
dependent on other viruses to replication
Adeno-associated virus
satellite virus – replicated only in cells infected with adenovirus
Delta agent
satellite virus – naked strand of RNA expressed only in the presence of HepB virus
Viroids
short pieces of RNA, no protein coat; only been identified in plants
Rabies
a bullet shaped animal virus that attaches to the nervous system for which a post exposure vaccine is a valid prevention method
RNA
type of nucleic acid in the core of the Influenza virus
False
TRUE OR FALSE: Bacteriophages may be grown on nutrient agar
Retrovirus
a virus such as HIV that produces revere transcriptase
Reverse transcriptase
an RNA-dependent DNA polymerase
Prophage
bacterium with hidden viral DNA with in its DNA
Herpes family
chicken pox, mono, shingles and cold sores are all caused by members of the same FAMILY of viruses
Arbovirus
general term for a virus carried by an arthropod vector such as a mosquito
