VIRUSES Biology 11

Small Pox

Measles

Chicken Pox

Do viruses have these characteristics? Are Viruses Alive? What makes something a living thing? Respond to a stimulus Made out of cells Require a constant energy supply Growth Potential for reproduction Do viruses have these characteristics?

Virus Structure Viral genome – nucleic acid. Could be DNA or RNA (retrovirus) Enzyme – to help with reverse transcription (RNA  DNA) or translation (RNA  protein) Capsid – protects the viral nucleic acid Envelope – usually on viruses that impact animal cells. Made of lipid bilayer. Help virus bind to specific cells in host

Edward Jenner Vaccines Discovered that milkmaids who contracted cowpox and recovered did not seem to be affected by the much deadlier small pox disease On the 14 May 1796, a young milkmaid called Sarah Nelmes came to see him with blisters like sores. He carefully extracted some liquid from her sores Jenner believed that if he could inject someone with cowpox, the germs from the cowpox would make the body able to defend itself against the dangerous smallpox germs which he would inject later.

Jenner’s Experiment Jenner made two small cuts on James's left arm. He then poured the liquid from Sarah's cowpox sores into the open wounds which he bandaged. James went down with cowpox but was not very ill. Six weeks later when James had recovered, Jenner vaccinated him again, this time with the smallpox virus.

A vaccine triggers the bodies memory B cells so that they cam recognize the proteins of the virus Usually includes capsid of envelope of virus, but no DNA

The Tobacco Mosaic Virus the first virus to be properly identified Causes a blotchiness on the leaves of tobacco crops making them unmarketable and worthless

How small are viruses?

Virus shapes helical – a hollow cylinder in the shape of a helix (coil) polyhedral – a regular shape of many sides, usually an icosahedron (20 sides) enveloped – a helical or polyhedral particle surrounded by an envelope complex – a wide variety of other irregular shapes

Bacteriophages viruses that only infect bacteria very specialised shape – like a little moon lander

Basic Viral Structure

Virus Replication Viruses do not reproduce, they replicate. In order to replicate, viruses require a host. Host cells provide all the materials that viruses need to copy themselves. If the viral capsule contains the same proteins and the host’s cell membrane, the virus attaches to the outside. The protein capsule shifts and inserts its nucleic acid (DNA or RNA).

The Lytic Cycle virus attaches to the receptor sites on the host it then inserts its genetic material into a host cell viral proteins are translated and viral DNA is replicated viral genes are enclosed in capsids during assembly of the new virus the host cell disintegrates (lysis) releasing the new bacteriophage

The Lysogenic Cycle the bacteriophage attaches to bacterial cell wall bacteriophage injects its DNA into host cell the DNA molecule then integrates itself into host cells DNA – integrated piece known as a prophage viral DNA joins onto a segment of the host’s chromosome – integrated molecule called a prophage the host cell multiplies as does the prophage within it without warning, the cell will become virulent and enter the lytic cycle, releasing many viruses

Phage Therapy Virus Specificity applies to bacteriophages as well We can use phages to attack specific bacteria. This eliminates many of the problems with antibiotics