Virus Introduction

What is a Virus? A small infectious agent that can replicate

only inside the cells of other organisms, bacteria, plants or animals.

Consists of at least two of three parts Genetic material, DNA or RNA (retro virus) Protein coat that protects the genetic material Possible lipid membrane

How do they compare to Bacteria?

They both can cause disease and have a similar structure

Are viruses alive? Viruses have characteristics that may

classify them as living. They also have characteristics that classify

them as non-living

They have no metabolism and cannot reproduce on their own so they do not qualify as a living organism.

How small are viruses?

Viruses are typically 20 – 400 nm

Bacteria are typically 1000 nm

4 Shapes of a virus Helical

Icosahedral

Envelope

Complex

Virus discovery and origin

In 1884 by French microbiologist Charles Chamberland

Origin is unclear because they do not leave behind any fossils or life evidence

The viruses that have been preserved by scientists date back about 90 years

There are 3 different theories of possible origin

1. Regressive Viruses may have been small cells that

parasitized larger cells and then lost unnecessary genes

2. Cellular May have evolved from bits of DNA, RNA or

plasmids that may have escaped or been lost 3. Coevolution

May have evolved from complex proteins and genetic material at the same time as cells first originated and are dependant on cells to stay in existence