CHARACTERISTICS OF VIRUSES

Are Viruses Living or Non-living?

Biologists consider viruses to be non-living because:– Are not cells– Do not grow or respond to their surroundings– Cannot make food, take in food, or produce wastes– Viruses do not respond to stimuli.

They can only multiply if in another living cell

What are Viruses?Definition-

Viruses are noncellular particles made up of genetic material and protein that can invade living cells.

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Discovery of Viruses

Beijerinck (1897) coined the Latin name “virus” meaning poison

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Tobacco Mosaic Virus

Wendell Stanley (1935) discovered viruses were made of nucleic acid and protein

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Smallpox

Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses

Smallpox has been eradicated in the world today

How Big is a Virus?

Viruses are very small – smaller than the smallest cell.

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Characteristics

Non living structuresNon-cellularContain a protein coat called the

capsidHave a nucleic acid core containing

DNA or RNA (one or the other - not both)

Capable of reproducing only when inside a HOST cell

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Characteristics

Some viruses are enclosed in an protective envelope

Some viruses may have spikes to help attach to the host cell

Most viruses infect only SPECIFIC host cells

CAPSID

ENVELOPE

DNA

SPIKES

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CharacteristicsOutside of host cells, viruses are inactiveViruses cause many common illnesses/ diseases

Some viruses may cause some cancers like leukemia

EBOLA VIRUSHIV VIRUS

MEASLES

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Characteristics

Viruses cause many common illnesses diseases

Some viruses may cause some cancers like leukemia

MEASLES

What do Viruses look like?

Viruses are unusual and different from other things in nature.

Viruses come in a variety of shapes

Some may be helical shape like the Ebola virusSome may be polyhedral shapes like the influenza virusOthers have more complex shapes like bacteriophages

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Types of Viruses: Helical Viruses

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Polyhedral Viruses

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Complex Viruses

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Viral Taxonomy

Family names end in -viridaeGenus names end in -virus Viral species: A group of viruses

sharing the same genetic information and ecological niche (host).

Common names are used for species

Subspecies are designated by a number

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Morophology– RNA or DNA Virus– Do or do NOT have an envelope– Capsid shape– HOST they infect

Used for Virus Identification

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Herpes Virus

SIMPLEX I and II

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Adenovirus

COMMON COLD

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Influenza Virus

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Chickenpox Virus

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Papillomavirus – Warts!

HOST SPECIFICITY

All kingdoms can be infected by viruses

Viruses are kingdom specific but they may or may not be species specific

Spread is specific to the type of virus

PARASITISM

Viruses are parasites.– A parasite is an organism that depends

upon another living organism for its existence in such a way that it harms that organism.

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Bacteriophages

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Cylces

Lysogenic Cycle– Viral DNA– May stay inactive in host for long periods of

time– Long lasting – Example Mono or chickenpox

Lytic Cylce– Short and can be over come – Example flu virus

Vaccine

Is a weaken form of the virus – To expose your immune system to the virus which

will allow your body to better fight off the virus when exposed to the full blow virus.

Vector Control

This is controlling the vectors that are carrying the virus.

Examples:– We stay home when sick, cover our mouth when

we cough etc. – We control the mosquito population in order to

control the West Nile virus

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Other Drug Treatments

Specific to certain viruses.

They don’t cure the virus but they can slow down and inhibit the multiplication of the virus.

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Reducing the RiskThey can’t be treated but they can be prevented!

Cover mouth/nose when you sneeze of cough

Wash hands frequently Avoid contact with the body fluids Not foolproof but reduces the risks