Viruses

Discovery of Viruses What is a virus? A nonliving particle made up of nucleic acid and a protein coat or a nucleic acid and a lipid-protein coat.

Discovery of Viruses Late 1800’s researchers found that something smaller than bacteria could cause disease 1935 Wendell demonstrated that viruses were not cells

Characteristics of Viruses Viruses are not living They cannot: Carry out metabolism or homeostasis Do not grow or divide Cannot reproduce outside their host cell

Viral Size and Structure Viruses are some of the smallest particles that are able to cause disease Shape is a result of its genome and the protein coat Two main structures: Capsid Envelope

Viral Size and Structure Capsid, or protein coat, is the only layer surrounding some viruses. These capsids have different shapes depending on the virus Envelope is a bilipid membrane that surrounds the capsid

Viral Size and Structure

Classification of Viruses Viruses are classified by: Whether they have RNA (Retrovirus) or DNA Nature of their capsid and the presence/absence of an envelope

Viral Replication Two ways for DNA viruses: DNA viruses can enter host cells and directly produce RNA Insert into a host’s chromosome, where they are transcribed to RNA along with the host’s DNA

Viral Replication RNA Virus Replication: The RNA genome of some RNA viruses can be directly translated to make viral proteins RETROVIRUS use reverse transcriptase and RNA as a template to make DNA

Viral Replication (Lytic) 1) Viruses attach to the surface of the host cell 2) The virus injects its genetic material into the cell. The viruses genetic material takes over many of the cell’s functions. 3) The viruses genetic material instructs the cell to produce the virus’s proteins and genetic materials

Viral Replication 4) The proteins and genetic material assemble into new viruses that fill the cell 5) The cell bursts open, releasing new viruses. The viruses go on to infect more cells

Viral Replication Bacteriophages Viruses that infect bacteria

Lytic cycle

Lysogenic In a lysogenic infection, a virus integrates its DNA into the DNA of the host cell The viral genetic information then replicates along with the host cell’s DNA Remains inactive for a period of time Viral DNA that is embedded in the host’s DNA is called a prophage

Viral Diseases Vectors (hosts) Humans Animals Insects Plants Bacteria

Human Viruses Vectors can transmit many viral diseases in humans like: Common Cold Flu HIV Hepatitis Rabies Chickenpox

Viral Diseases Some viruses contain oncogenes, which are cancer causing agents. Emerging viruses usually infect animals isolated in nature but can jump to humans when contact occurs in the environment

Prevention and Treatment Vaccinations A vaccine contains a harmless version of a virus, bacterium, or a toxin that causes an immune response when introduced to the body Vector Control Controlling insects and quarantining people have reduced the spread of diseases

Drug Therapy Antibiotics are ineffective against viral diseases Viral drugs, such as acyclovir, block reproduction in viral replication.

Viroids and Prions Viroids Short, circular, single-strands of RNA lacking a capsid that infect plant cells Prions Infectious particles that contain proteins but no nucleic acids Cause Mad Cow disease and other degenerative brain diseases

Influenza Virus Caused by RNA virus Changes every year Typically transmitted through the air or direct contact Attacks the tissues in the lungs Influenza of Pandemic 1918 Pandemic: disease that infects numerous people across continents

Influenza Virus

Common Cold RNA Virus Changes all the time Most frequent infectious disease in humans Infects the tissues in the lungs Transmitted through direct contact or through the air

Polio DNA Virus Primarily transmitted by fecal-oral Attacks tissue in the central nervous system

HIV Human Immunodeficiency Virus RNA Virus Routes of Transmission: Transfer of bodily fluids Transfer of blood Attacks your immune system Causes AIDS