1. Learning Target: Virus Anatomy and Physiology
I Can… Explain how viruses infect host cells and manipulate the host cell into manufacturing more viruses.
I Will…
Identify the fundamental structural components of a virus
List general characteristics of viruses
Describe two common ways viruses infect host cells
Describe the two types of viral infection pathways

2. Learning Target: Virus Anatomy and Physiology
Virus – Infectious particle made only of a nucleic acid strand (either DNA or RNA) surrounded by a protein coat
Nucleic acid
Single strand, double strand
Linear, circular or segmented
Protein coat – Capsid
Individual protein components
Different shapes
Some viruses have a lipid layer
Spikey surface protein and sugar structures
Used to attach to host cell
Can be used to identify the virus

3. Learning Target: Virus Anatomy and Physiology

4. Learning Target: Virus Anatomy and Physiology

5. Do not carry on metabolism Inactive outside of the host cell
Learning Target: Virus Anatomy and Physiology
Viruses
Do not have ribosomes
Cannot make enzymes
Cannot make proteins
Do not carry on metabolism
Inactive outside of the host cell
Unable to reproduce without host cell
Cannot copy DNA
Viruses are NOT alive

6. Learning Target: Virus Anatomy and Physiology
Virus shapes act lock-and-key
Can only infect certain cells
Spikes bind to cell membrane proteins
Usually species specific
e.g. Tobacco Mosaic Virus
Some viruses can cross between different species
e.g. H1N1 (Swine flu)
Some viruses start in birds
Mutate and pass to another species such as pigs
Mutate again and infect humans
Rabies virus infects all mammals

7. Two common ways viruses infect host cells
Learning Target: Virus Anatomy and Physiology
Two common ways viruses infect host cells
Simple Injection
Virus attaches to cell surface
Injects nucleic acid into cell’s cytoplasm
Like a syringe
e.g. T-Bacteriophage
Endocytosis
Eukaryotic cells infected
Virus fuses with the cell membrane receptors
Releases capsid into cytoplasm in vesicle
e.g. HIV
Continue

8. Learning Target: Virus Anatomy and Physiology
T-Bacteriophage infects E. coli bacteria
Simple injection method
Return

9. Learning Target: Virus Anatomy and Physiology
Viral RNA uses Reverse Transcriptase enzyme to make Viral DNA genes
Return

10. 2 basic types of infection pathways occurs
Learning Target: Virus Anatomy and Physiology
Once virus nucleic acid is inside host cell,
2 basic types of infection pathways occurs
Lytic Cycle:
Virus nucleic acid takes control of host DNA
Turns on host genes to copy virus genes
Viral genes direct transcription and translation of proteins
Capsids
Enzymes
Enzymes help copy viral DNA
Host cell energy assembles viral parts
Viral enzymes dissolves host cell membrane
Destroys host cell and releases new viruses
Lytic Cycle

11. Learning Target: Virus Anatomy and Physiology
Lysogenic Cycle: Virus combines its DNA into DNA of the host cell (Recombinant DNA)
Viral DNA genes inserted into host DNA
New set of genes
Prophage in bacteria
Provirus in other organisms
New genes may change cell traits
e.g. HPV link to cervical cancer
Cell goes through mitosis
Daughter cells get identical copies of new genes
Two Paths:
Dormant and continued passing through mitosis
Activated by stress trigger
Enters Lytic Cycle and destroys cell
e.g. Herpes viral cold sore

12. Learning Target: Virus Anatomy and Physiology
Lytic Cycle or Lysogenic Cycle
Return

13. Learning Target: Virus Anatomy and Physiology
Lytic Cycle
Virus is a “Bad house guest”
Moves in
Trashes the place
Blows up the house
Leaves for new house
Lysogenic Cycle
Virus moves in
Stays and does not leave
If stressed
Blows up house and leaves for new house

14. Learning Check √: Virus Anatomy and Physiology
Name the two ways in which a virus (or virus’ DNA) can enter a cell:
__________________________
What are the two viral infection cycle pathways?
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3. Why can’t you catch most viruses that infect plants or other animals.