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

Continue

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

Infectious agent

Reservoir

Host

Portal of Exit

Transmission

Portal of Entry

Susceptible Host

Infectious agent• Bacteria• Virus

You

Blood/body fluids• Secretions• Wound

Direct/Indirect • Contact• Droplets• Airborne

Respiratory DigestiveWound

Low resistance individual

Learning Target: Communicable Disease Chain of Infection

Breaking Chain of Infection

Infectious agent

Reservoir

Host

Portal of Exit

Transmission

Portal of Entry

Susceptible Host

IsolationPrompt treatment

Cover mouth/NoseWoundBandage

Hand washing, Sanitation, Disinfection

GlovesMaskBandage

VaccinationRestNutrition