Virus NotesTEK 4C

• Viruses are composed of nucleic acids enclosed in a protein coat and are smaller than the smallest

bacterium.

What is a Virus?

Viruses are considered nonliving because:

• They are NOT cells.• They don’t carry out respiration, grow, or develop. • They do not reproduce like living cells.

What is a Virus?

What is a Virus?

•Viruses cannot reproduce without the help of a living cell.

•Viruses infect a host cell and inject their DNA/RNA.

• A cell in which a virus replicates inside of is called the host cell.

What is a Host Cell?

Before a virus can replicate, it must enter a host cell.

• A virus recognizes and attaches to a host cell when one of its proteins attaches with a molecular shape that is the receptor site on the host cell’s plasma membrane.

Virus

• Each virus has a specifically shaped attachment protein. Therefore, each virus can usually attach to only a few kinds of cells.

• In general, viruses are species specific, and some also are cell-type specific. For example, polio viruses normally infect only intestinal and nerve cells.

Viral Attachment to Host

• A virus has an inner core of nucleic acid, either RNA or DNA

and an outer protein coat called a capsid.

Capsid

Nucleic acid

Viral Structure

• Some larger viruses, such as human flu viruses, may have an additional layer, called an envelope, surrounding their capsids.

Capsid

Nucleic acid

Envelope

Viral Structure

• Envelopes are composed primarily of the same materials found in the plasma membranes of all cells.

Polyhedral virus shape

Human Papilloma Virus

Envelope studded with projections

(flu and AIDS)

VIRUS SHAPES

Long narrow helical shape (Tobacco Mosaic

Virus)

Polyhedral-shaped head attached to a cylindrical tail

with leg-like fibers

VIRUS SHAPES

Viruses and Disease

• A vaccine is an injection of particles of viruses or bacteria that provide the human body with a defense against disease.

• Antibiotics are ineffective against viral infections.

• For bacterial infections, antibiotics are a good option.

Common Viral DiseasesInfluenza

Common Cold

Chicken Pox

Common Viral Diseases

Small Pox

HIV / AIDSHIV attacking T-Cell

West Nile VirusTransmitted by mosquito