Microbiology 251- Ch.6

Describe the main characteristics of viruses:

-Infectious
-Acellular
-Cannot be seen by light microscope (need electron microscope)
-Requires host cell to replicate
-Specific for cell type/host

Can viruses be grown in pure culture?

No

Describe viral genetic structure:

-Either DNA or RNA but never both
-Single or double stranded
-Small genome

What do viral genomes code for?

-Viral protein coat
-Proteins for nucleic acid replication (once in host cell)
-Proteins needed to get into cells

How are viruses usually classified?

-Based upon what cell type they infect (Euk/Prok)
-Ex: Bacteriophage (phage)
-Ex: Species or organ system

Explain the structure of a virus

Nucleic acid surrounded by capsid

What is a capsid?

-Protein coat surrounding virus

What is a capsomere?

-Subunits of capsid

What is a nucleocapsid?

-Capsid and nucleic acids together

What are the three shapes of viruses?

-Polyhedral/Icosahedral (20 flat triangles)
-Helical (helix)
-Complex

What is an enveloped virus?

-Virus surrounded by lipid bilayer (obtained from host cell)
-Has matrix protein b/w nucleocapsid and envelope

What is a naked virus?

-Non-enveloped virus
-More resistent to disinfectants

What are protein spikes?

-Protein structures from capsid
-Attach to receptor sites on host cells
-Phages attach by tail fibers

How does the Baltimore Classification System classify viruses? (5)

-Genome structure
-Shape
-Mechanisms of replication
-Envelope presence/absence
-Disease/symptoms it causes

What are the routes of viral transmission?

-Enteric (polio, rotovirus)
-Respiratory (influenza, measles, rhinovirus)
-Zoonotic (rabies, west nile virus)
-Arboviruses (anthropods)
-Sexually (HSV, HIV, hepatitis)

Where does bacteriophage replication happen in cell?

-Cytoplasm of bacteria

Where does viral replication happen in eukaryotic cell?

-Nucleus (for most)
-Cytoplasm in large DNA viruses

How do viruses get into cells?

-Bind to one or more receptor cites on host cell
-Then, either endocytosis (non-enveloped) or fusion with host cell membrane (enveloped)
-Bacteriophages inject their DNA into cell

How do viruses get out of cells?

-Most enveloped leave via budding
-Most non-enveloped leave when host cell lyses

List the steps of viral replication

-Attachment/Adsorption
-Penetration
-term-31Uncoating/genome release
-Synthesis (DNA/proteins)
-Assembly/maturation
-Release

Difference b/w Virulent and Temperate phage

-Virulent- Causes lysis/death of cells
-Temperate- Becomes part of host chromosome/induces host to make new viruses

What are the steps of lytic bacteriophage replication?

-Phage binds to receptors
-Phage DNA is injected into cell
-Transcription (production of viral encoded DNA)
-Replication of phage DNA
-Transcription (translation of capsid/lysis proteins)
-Cell lyses/Phage is released

Define Prophage

Bacteriophage DNA becomes embedded in bacteria's DNA

Define Lysogen

A bacterium containing a prophage

Define lysogenic conversion

-When phenotype (properties) of a bacterial cell are changed due to carrying a phage

What are some properties encoded by prophages?

-Toxin secretion
-Membrane modification
-Virulence factors