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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 Characteristics of viruses
• Describe two common ways viruses infect host
cells
• Describe the two types of viral infection
pathways
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
Learning Target: Virus Anatomy and Physiology
Learning Target: Virus Anatomy and Physiology
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
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
Learning Target: Virus Anatomy and Physiology
Two common ways viruses infect host cells
1) Simple Injection
• Virus attaches to cell surface
• Injects nucleic acid into cell’s cytoplasm
• Like a syringe
• e.g. T-Bacteriophage
2) Endocytosis
• Eukaryotic cells infected
• Virus fuses with the cell membrane receptors
• Releases capsid into cytoplasm in vesicle
• e.g. HIV
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Learning Target: Virus Anatomy and Physiology
T-Bacteriophage infects
E. coli bacteria
• Simple injection method
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Learning Target: Virus Anatomy and Physiology
Viral RNA
uses Reverse
Transcriptase
enzyme to
make Viral
DNA genes
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Learning Target: Virus Anatomy and Physiology
Once virus nucleic acid is inside host cell,
2 basic types of infection 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
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
Learning Target: Virus Anatomy and Physiology
Lytic Cycle or Lysogenic Cycle
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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
• Trashes the place
• Blows up house and leaves for new house
Learning Check √: Virus Anatomy and Physiology
1. Name the two ways in which a virus (or virus’
DNA) can enter a cell:
a) __________________________
b) __________________________
2. What are the two viral infection cycle
pathways?
a) _________________________
b) _________________________
3. Why can’t you catch most viruses that infect
plants or other animals.
Learning Target: Communicable Disease Chain of Infection
I Can… Describe how communicable diseases are
transmitted and how the chain of infection can be
broken.
I Will…
•Define the terms; Pathogen, Infectious,
Disease, and Communicable
•List different types of disease categories
•Diagram the chain of infection in
communicable diseases
•Provide examples of ways to break the chain of
infection at each link
Learning Target: Communicable Disease Chain of Infection
Pathogen – Any living organism or particle
that can cause an infectious disease.
• Infectious – capable of causing an
infection
• Disease damaging change in structure or
function of cells, tissues, etc…
• Communicable – able to be passed from
host to host
• “Contagious”
• Host cell – cell infected by pathogen
• Contagion – another name for a pathogen
Learning Target: Communicable Disease Chain of Infection
Communicable Diseases
• Differs from other diseases
• Types of disease categories
• Genetic – inherited through the DNA e.g.
Cystic Fibrosis, Color blindness
• Congenital – born with condition, but
not genetically based
• Environmental/Chemical – brought on
by exposure to environmental factors
such as U.V. light (skin cancer) or
chemical such as Tar/nicotine (lung
cancer)
• Communicable – caused by a pathogen
and can be passed from host to host
Learning Target: Communicable Disease Chain of Infection
Chain of Infection
Low resistance
individual
Respiratory
Digestive
Wound
Infectious
agent
Infectious agent
• Bacteria
• Virus
Susceptible
Host
Reservoir
Host
Portal of
Entry
Portal of
Exit
Direct/Indirect
• Contact
• Droplets
• Airborne
Transmission
You
Blood/body fluids
• Secretions
• Wound
Learning Target: Communicable Disease Chain of Infection
Breaking Chain of Infection
Vaccination
Rest
Nutrition Susceptible
Infectious
agent
Reservoir
Host
Host
Gloves
Mask
Bandage
Isolation
Prompt
treatment
Portal of
Entry
Portal of
Exit
Transmission
Hand washing, Sanitation, Disinfection
Cover
mouth/
Nose
Wound
Bandage