Viral size range

20 nm – 250 nm

Viral genome

Contains the nucleic acid --- Either DNA or RNA

Capsid

a protein shell enclosing the genome ---Made up of capsomeres

Viral envelope

A membranous covering over the capsid studded with glycoprotein receptors, it allows for easier access into a host cell, and is supplied by the host cell upon exit from the cell

Rhinovirus

Causes the common cold A naked virus with three different proteins comprising the capsomeres of the capsid.

Tobacco mosaic virus (TMV)

--Consists of a rigid, rod-shaped capsid surrounding RNA --The capsid consists of over 1000 capsomeres of a single type of protein --Capsomeres are arranged in a helix

Adenoviruses

--Icosahedron shape---that the capsid consists of 252 identical protein capsomeres arranged in a polyhedral shape with 20 triangular facets --The capsid surrounds DNA

Influenza viruses

--This is a virus with an outer envelope studded with numerous glycoprotein receptors. --The envelope surrounds eight RNA molecules each within its own capsid. --Different strains of influenza vary based on their RNA base sequences.

Bacteriophages (T4)

--Have the most complex viral capsids --Each capsid consists of a head, tail sheath and tail fibers. --The head contains DNA

1883 – Adolf Mayer

--Studied diseased tobacco plants – Demonstrated transmission by rubbing sap from diseased leaves to healthy ones – He was unsuccessful in identifying infectious agent – Assumed pathogenic agent was a small bacterium

1893 – Dimitri Ivanovsky

– Applied filtered sap from diseased leaves to healthy ones – The filtering process was known to remove bacteria – The infectious agent remained in the sap and infected healthy leaves – Assumed the infectious agent must be a small unfilterable bacterium

Early 1900’s – Martinus Beijerinck

– Performed serial infections where he continually diluted the sap prior to applying to healthy leaves. – Demonstrated that the infectious agent was reproducing and did not lose its potency – He was unable to culture it on nutrient media – Assumed that the infectious agent must be smaller than bacteria and only reproducing within host cells – Coined the term “virus” meaning poison – First to consider that the pathogenic agent was not a bacterium.

1935 – Wendell Stanley

– Crystallized the infectious particle and identified its structure through X-ray crystallography – Called the agent TMV = tobacco mosaic virus

lysogenic cycle of bacteriophage replication

– It allows the phage DNA to get incorporated in the bacterial chromosome as a prophage. – This cycle prevents the complete elimination of a bacterial population

lytic cycle of bacteriophage replication

results in the rupturing of the host cell bacterium when releasing the newly produced phages

Virulent phages

only perform the lytic cycle of replication.

Temperate phages

can perform both lytic and lysogenic cycle of replication

Restriction enzymes (also called restriction endonucleases)

Is a bacterial defense that that immediately degrade the phage DNA when it is injected into a bacterium by a bacteriophage

Baltimore System of Classification Class I

Animal viruses with ds DNA

Baltimore System of Classification Class II

Animal viruses with ss DNA

Baltimore System of Classification Class III

animal viruses with ds RNA

Baltimore System of Classification Class IV

animal viruses with ss RNA --(RNA serves directly as mRNA when in host cell)

Baltimore System of Classification Class V

animal viruses with ss RNA --(RNA used as a template for mRNA synthesis in host cell)

Baltimore System of Classification Class VI

animal viruses with ss RNA --(RNA used as a template for SNA synthesis in host cell)

what class is HIV – Human Immunodeficiency Virus

--Class VI animal virus

Opportunistic infections

Infections that arise secondarily due to increased viral load and low helper T-cell levels

What type of infection is AIDS

It is an Opportunistic infection when paint has vary low helper T-cell levels from the original exposed to HIV

What does a viral infection of plants do to the plant?

It causes "breaking" or streaking of tulip flower color, or irregular brown colors on fruits and vegetable, not allowing them to ripen

Viroids

-Viral-like infectious particles that infect plants --Are infectious circular RNA molecules

Prions

-Viral-like infectious particles that infect animals --Are infectious protein molecules and interferes with nerve cells communicating