Chapter 10.1 Viruses Flashcards
What is pathology?
The study of specific diseases caused by microorganisms and the strategies used to combat them.
What is a pathogen?
Foreign invaders that cause disease
What are 4 examples of pathogens?
- Viruses
- Bacteria
- Fungi
- Protists (parasites)
What is a virus?
- The smallest of the infectious agents - 18-300nm in diameter
- Considered biologically inert - somewhere between simple biomolecules (ie: proteins, DNA) and living organisms (bacteria)
- Cannot be seen with light microscopes
- Estimated to be 100 families with 2,800 species of viruses (this number rises every year)
- Not all viruses infect humans
Why are viruses not considered to be alive?
They do not meet the basic criteria scientists use to characterize life
- They DO NOT perform metabolism
- They have no capacity to reproduce (by itself)
- DO NOT respond to stimuli
- No cellular composition (acellular)
- No complex growth
When and how were viruses discovered?
Discovered in the late 19th century
Scientists were studying sap from plants and the sap would transmit disease, but no bacteria present in the plant. Sap was filtered to remove all bacteria, but still transmitting disease!
Scientists concluded the agent must be way smaller than simpler bacteria but couldn’t be cultured in lab
What are the components of the structure of a virus?
Genetic material (DNA or RNA) inside a protein casing.
Envelope protein Envelope Viral genome Capsid Viral tegument
NO membranes, organelles, nucleus or cytoskeleton
What is a capsid?
The protein shell that encloses the genetic material
What are capsomeres?
Smaller pieces that make up the capsid
What are some common viral structures?
- Rod-shaped or helical
- Icosahedral - solid with 20 faces
- Membranous envelope covered in spikes
- Bacteriophage - rod and icosahedral mixture, comples structure that looks like weird, little spiders
What is an example of rod shaped or helical virus?
Tobacco mosaic virus
What is an example of a icosahedral virus?
Adenovirus
What is an example of a membranous envelope shaped virus?
Influenza, coronavirus
What do viruses need to replicate?
Because they don’t have ribosomes to express genes, they need a cell to do it for them!
What are the steps in replication?
- Recognition
- Injection
- Transcription and translation
- Reassembly
What is necessary for recognition?
- A virus must be recognized by a specific type of cell in order to enter that cell
- Usually contains specificity for a small group of species or one specific species
What happens during injection?
The virus injects its genetic material OR is brought into the cell, completely intact through endocytosis
What happens during transcription and translation?
The virus disassembles and the viral DNA is transcribed and translated by the host cell
What happens during reassembly?
Once there are many copies of the viral DNA, the capsid protein re-assembles and releases new viral particles.
Sometimes this destroys the cell.
What is the lytic cycle?
The host cell is terminated at the end of the replicated cycle.
It happens once many viruses have been generated.
The cell lyses and releases viral particles.
What is the lysogenic cycle?
The host cell is not destroyed when the viral DNA enters the cell
Rather than hijacking the cell, the virus inserts its viral DNA into the host’s genome creating a prophage.
The cell continues to replicate, where the DNA remains silent.
An environmental signal causes a switch to the lytic cycle, causing all infected cells to lyse.
What is lysis?
The disintegration of a cell by rupture of the cell wall or membrane
What is endocytosis?
Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material.
What is a prophage?
Viral DNA that is embedded in the host’s DNA during lysogenic infection
What is important about membrane and surface receptors?
It is important for the virus to be recognized by the surface cell receptors.
The receptors allow the virus to enter and exit WITHOUT damaging the cell.
What is a retrovirus?
It contains an enzyme called reverse transcriptase, which makes RNA into DNA.
What is an example of a retrovirus?
HIV
What are viroids?
Even smaller infectious agents
Naked, circular RNA molecules that disrupt regulatory systems in plants
What are prions?
Contain no genome.
Infectious protein particles that cause other protein particles to aggregate and bring on disease symptoms.
What are examples of prions?
Alzheimer’s and Parkinsons’s
