Viruses Flashcards
Midterm 2
Obligate Parasites
Viruses are NOT living creatures until they have attached to and invaded a living organism
DNA viruses
Hepatitis B
Herpes Simplex 1 (cold sores)
Herpes Simplex 2 (genital herpes)
Herpes Simplex 3 (Varicella Chicken Pox & Zoster Shingles)
Herpes Simplex 4 Infectious Mononucleosis (Epstein-Barr Virus)
HPV (genital warts)
Smallpox (Variola)
RNA Viruses
Influenza
Red Measles (Rubeola)
Pneuomonitis/Bronchiolitis (Respiratory Syncytial Virus RSV)
HIV and AIDS
Norovirus
Polio
German Measles (Rubella)
Hepatitis A and C
West Nile Virus
COVID19 (SARS)
Approximate size of viruses
Extremely tiny, within the realm of nanometers (bacteria are within the realm of micrometers)
How do viruses attach?
Viruses are host-specific and attach to receptor sites
1. Enveloped viruses take a bit of the host’s membrane system with them and are pleomorphic since the envelope is more supple than the capsid (glycoprotein spikes for attachment)
2. Non-enveloped viruses have only the capsid layer protecting the genetic material (capsid molecules for binding and attachment)
Types of Virus Morphology
-Helical
-Polyhedral
-Enveloped & Spherical
-Complex
Methods of Culturing Viruses
-Viral Plaque Method
-Animals and Transgenic animals
-Tissue Culture Method
-Cytopathic Effects
-Embryonated Eggs
Culturing
Viral Plaque Method
Growing a virus over a layer of bacteria on a plate (plaques are the holes in the bacterial layer which indicated areas of host cell death aka zone of lysis by virus)
Culturing
Tissue Culture Method
grow tissue cultures and put viral cells on them, watch them go
Culturing
Cytopathic Effects
unleash virus on host tissue and look for cytopathic effects (patterns) (can be used on chick and rat embryo cells)
Culturing
Embryonated Eggs
embryonated eggs have a variety of areas doe viruses to targets, eggs are innoculated with virus and are cultivated MOST COMMON METHOD USED TODAY since eggs are cheap and readily available
Methods of diagnosing virus
-Electron microscopy (to look at size, structure, and number & arrangement of capsomeres)
-CPEs, inclusion bodies in host tissue
-Serology
-Nucleic acid probes
T-Even Phages
-Important structures include the Polyhedral Capsid Head, DNA (genetic information), Helical Tail, Tail Sheath, Pin & Plate, and Tail Fibers
-Not enveloped and only attach to bacteria
-Best understood and most studied virus
T-4 Virus
Virus that typically parasitizes E. coli organisms
Life Cycle of Bacteriophage
- Attachment
- Penetration/Entry
- Biosynthesis
- Assembly/Maturation
- Release
Attachment
Tail fibers attach to host receptor proteins (very specific because of this) via random collision
Penetration/Entry
Bacteriophage injects hydrolytic enzyme into host cell by contracting tail sheath and forcing the internal hollow tube within the tail through the host’s cell wall and membrane (like a hypodermic syringe)
*Bacteriophages for animal viruses enter via endocytosis, fusion, or direct penetration (non-enveloped bacteriophages)
Biosynthesis
After entry, enzymes degrade the bacterial DNA and Bacterium stops synthesizing its own molecules and begins synthesizing new viruses under the direction of the viral genome
Assembly/Maturation
Not entirely understood
Parts of the bacteriophage accumulate within the cell and spontaneously attach to each other to form new virions
Transduction
Transfer of DNA from old host to new host when the viral capsid assembles around pieces of host DNA
Release (bacteriophage life cycle)
Viruses are released from the host bacterial cell as the lysozome completes its degradation of the host’s wall and the bacterium lyses
-Non-enveloped: released from animal cells through exocytosis, which may cause lysis and death of the cell
-Enveloped: often released through budding or exocytosis. Virus exits cell with envelope derived from a plasma or organelle membrane. Host cells die eventually due to all the damage from the viral occupants
Eclipse Period
the time period from attachment to pre-assembly where virions penetrate host’s cells. (time between successful cell infection and start of virus production)
Burst Time
the time period from attachment to release (lysis). The number of virions released per infected bacterium
Latency
when animal viruses remain dormant in host cells. In asymptomatic host, viruses are not usually released unless activated (Herpes Simplex, Chicken Pox/Shingles)
