VIRUSES

VIRUSESAvian

influenza AH5N1 virus

VIRUSES

Virus Definition & Criteria• infectious agent with both

living and nonliving characteristics that is totally dependent on a host cell for replication (intracellular parasite)

• contain only either DNA or RNA, but not both

• viral genome directs the synthesis of viral components using host cell machinery

VIRUSES

Virus Definition & Criteria• newly synthesized viral

components are assembled into a new complete virus called a virion (pronounced vye-ree-on) which can then infect another host cell

• bacteriophage: virus that infects only bacteria

• mycophage: virus that infects only fungi

VIRUSES

Multiple virions of

yellow fever virus, the

first human virus

discovered in 1901.

Living characteristics of viruses • reproduce at a fast rate, but only in

living host cells• can mutate / evolve

Nonliving characteristics of viruses

• are acellular (no cytoplasm or organelles)

• not autonomous: carry out no metabolism on their own (i.e. viruses don't grow and divide)

• replication is fully dependent on the host cell's metabolic machinery; viral components are synthesized and assembled within the infected host cell

VIRUSES

VIRUSES

SARS related Corona viruses

Viral SizeViruses are usually much smaller than bacteria and are submicroscopic. Most range in size from 5 to 300 nm. Thus viruses can infect even other microorganisms.

Animal RNA Virus

Animal DNA Virus Bacteriophage

Viral Structure

A virus consists of these main parts:

• Genome (DNA/RNA)• Capsid (protein)• Envelope (lipid) capsid

genome

VIRUSES

Genome

• Genetic material of the virus that codes for the synthesis of viral components and viral enzymes for replication

• Can be DNA or RNA but not both

• Can be single or double stranded

• Can be a circular or linear molecule

• Can be a single unit or segmented into parts

VIRUSES

Which Human Diseases Are Caused By Viruses?

• Infectious diseases

DNA viruses

Respiratory disease

Smallpox

Chicken pox

Mononucleosis

Cold sores

RNA viruses

AIDS

Influenza (flu)

Common cold

Polio

Measles

Rabies

VIRUSES

Capsid (core)

• A protein shell surrounding the genome.

• Protects and introduces the genome into host cells.

• Viruses that consist of only a genome surrounded by a capsid and are called nucleocapsid or naked viruses.

Nucleic acid

Envelope

Capsid

VIRAL STRUCTURE

Envelope

• Most animal viruses have an envelope

• Composed of phospholipids and glycoprotein

• Usually derived from host cell membranes by a process called budding.

Nucleic acid

Envelope

Capsid

VIRAL STRUCTURE

Electron Micrograph of HIV Budding from a T4-Lymphocyte

Virus Obtaining Its Envelope from Host Cell Membrane by Budding

VIRAL STRUCTURE

Chicken Poxvaricella-zoster virus (VZV)

DNA Virus

PolioPoliovirus

RNA Virus

It is found in areas where water treatment and sanitation facilities are not properly maintained or non-existent. Although children under three years of age represent more than half of all cases polio can affect people of any age.

Nonparalytic polio causes symptoms that mimic the flu. Sore throat, fatigue, nausea, diarrhea, a fever, or vomiting. Most cases of nonparalytic polio clear up in a number of days, but a some people go on to develop meningitis, a condition in which the lining of the brain is infected. When a person develops paralytic polio, destroys nerves that control muscles. The infection may be fatal if the brain and respiratory organs become affected.

Polio is a serious condition that causes paralysis in about 1% of those infected (paralytic polio).

HerpesDNA Virus

Herpes Simplex 1 and herpes simplex 2.

The sores are sometimes accompanied by other symptoms such as:headache, fever, and other flu-like symptoms pain, itching, tingling, or tenderness around the genitals painful urination, swollen tender points in the groin and lower abdomen

Genital WartsHPV – human papillomavirus

DNA Virus

HIV – Human Immunodeficiency Virus

HIV MYTHS

http://www.youtube.com/watch?v=LaVm3moZo_g

http://www.youtube.com/watch?v=68I7JlVhuhY&feature=related