Viruses

VirusesChapter 18

VIRUS: Latin word for poison Virus: Non-living, parasitic, biological particle.All viruses cause some sort of disease. Some even cause cancer.VIRUSES do not live because:They can not reproduce outside a host cell

They do not carry out cellular respiration

They do not grow or developVirus structureDNA or RNA CoreHolds the genetic material that will affect the host

CapsidOuter protein coat that enables the virus to enter certain cells.

Virus structureGlycoproteinsProjections that help the virus attach to hostNot all viruses have glycoproteins.

Virus Size

Viruses are smaller than the smallest cell

Virus VocabHost: a cell in which a virus replicatesHost Specific: most viruses or bacteria will only affect a single host or a small group of host speciesExamples:West Nile Virus affects birds, horses, and peopleInfluenza type B affects only people not othersParvo affects only dogs, not other organisms

Types of Viruses

Bacteriophages

PhagesViruses that attack bacteria are called bacteriophage or just phageT-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails

T-phagesThe most commonly studied T-phages are T4 and T7They infect E. coli , an intestinal bacteriaSix small spikes at the base of a contractile tail are used to attach to the host cell Inject viral DNA into cell

Viruses Blow Up the Cell the Affect!!!Once the viral genes get inside a cell, the genes are expressed.This genetic program causes the host cell to make copies of the virus.In the process, the host cell is destroyed.

Viruses Blow Up the Cell they Affect!!!There are two ways this can occurThe Lytic CycleThe Lysogenic Cycle

The Lytic CycleSTEPSAttachVirus docks with host cellInjectionVirus inject its DNA/RNA into host cellReplicatereplication of virus partsLysiscell ruptures and new virus invade tissues of the host

Lysis to break or rupture cells or cell membranesThe Lysogenic CycleSTEPSAttachVirus docks with host cellInjectionVirus inject its DNA/RNA into host cellIncorporateDNA attaches to the cells own DNA Time Goes ByStressReplicatereplication of virus partsLysiscell ruptures and new virus invade tissues of the host

Examples of Lytic Viral Infections

1. Common ColdHow do we catch it?Contact with contaminated objects; droplet inhalationWhat are the symptoms?Sneezing, Sore Throat, Fever, Headache, Muscle Aches

Examples of Lytic Viral Infections2. InfluenzaHow do we catch it?Contact with contaminated objects, droplet inhalation.What are the symptoms?Body Aches, Fever, Sore Throat, Nasal Congestion, Headache, Dry Cough, Fatigue.

Examples of Lytic Viral Infections3. EbolaHow do we catch it?exposure to blood or bodily secretions of an infected person, or through direct contact with the person.What are the symptoms?Sore Throat, Fever, Dry hacking cough, Weakness, Severe Headache, Joint and muscle aches, Diarrhea, Dehydration, Stomach pain, vomiting, Internal and external bleeding.

Examples of Lysogenic Viral Infections1. Herpes VirusesOnce a person is infected with a herpes virus they are infected for life.Examples: Chicken Pox can reappear later in life as ShinglesHSV-1 (oral herpes) and HSV-2 ( genital herpes)

19Example of a Retrovirus

2. HIVHow do we catch it?Contact with contaminated blood or bodily fluidsWhat are the symptoms?T cells (needed for normal immune function) are destroyed

RetrovirusesRetroviruses are viruses that contain RNA as their genetic informationRetroviruses get their name from the fact that their genetic information is copied backward, from RNA to DNA.HIV is the most infamous retrovirus

How Do Our Bodies Fight Viral Infections?Antibiotics do nothing for viral infections!!!After enough cell debris (from blown up cells) is detected your Immune system gets involved

Macrophages are large white blood cells that get rid of debris by eating it.

When they eat too much, they die. These dead cells and the cell debris are puss

How Do Our Bodies Fight Viral Infections?Other white blood cells pick up viral particles from the battle and carry it to Lymph nodes.In the lymph nodes, they look for cells to fight this type of virus.

T- cells (thyroid cells) are called upon and go to the site of the infection to kill specific infected cellsB-cells (bursal cells) make antibodies that go to the site and kill free viruses

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How Do Our Bodies Fight Viral Infections?The best way to protect against most viral diseases lies in prevention, often by the use of vaccines.Most vaccines provide protection only if they are used before an infection begins.