Adenovirus - cause of the common cold Viruses Viruses are insidious pathogens, they attack cells from the inside.  They hijack your own DNA and use it against you.  A virus cannot be treated with antibiotics, it can only run its course until your immune system kicks it out. ..Even then, the virus may lay dormant within the cells and come back at a later date

What is a virus? an infective agent that typically consists of a nucleic acid molecule in a protein coat and sometimes a membrane (envelope), is too small to be seen by light microscopy, and is able to multiply only within the living cells of a host.

Properties of viruses No cytoplasm, ribosomes, or other cellular components they cannot move or grow they can only reproduce inside a host cell they consist of 2 major parts - a protein coat, and hereditary material (DNA or RNA)- sometimes a “membrane” they are extremely tiny, much smaller than a cell and only visible with advanced electron microscopes

Virus Structure

Parasitic Nature  Obligate intracellular parasites (they cannot exist independently) Specific to hosts (human, dog, some can cross species)  Specific to cells , the common cold (rhinovirus) is a virus that specifically attacks cells of the respiratory track (hence the coughing and sneezing and sniffling). HIV specifically attacks white blood cells This is a bacteriophage, a type of virus that attacks bacteria. It is recognizeable because it looks like the lunar landing spaceship.

2. Penetration - the virus is engulfed by the cell How do Viruses Reproduce? 1. Attachment 2. Penetration - the virus is engulfed by the cell 3. Biosynthesis - viral components are made (protein coat, capsid, DNA/RNA) 4. Maturation - assembly of viral components 5. Release - viruses leave host cell to infect new cells   (often destroys host)

Viral Reproduction  Lytic cycle = reproduction occurs, cells burst Lysogenic cycle = reproduction does not immediately occur (dormancy)  Virulent = viruses that undergo both cycles

Lytic vs Lysogenic Pathways of viruses

Retroviruses -- RNA viruses that have a DNA stage Human Immunodefiency Virus - causes AIDS  Retrovirus (RNA inside a protein coat)  Reverse Transcriptase makes DNA from the virus RNA  DNA inserts into host DNA  Proteins are assembled from the DNA code  Viruses assembled from the proteins  Viruses released from the cell

Developing a vaccine for AIDS is difficult because it is a RETROVIRUS Developing a vaccine for AIDS is difficult because it is a RETROVIRUS.  RNA mutates easily and each individual virus can be slightly different from the others.  In fact, different viruses can exist within the same person.

Related to Viruses  Viroids - even smaller than viruses, consist of RNA strands that lack a protein coat Prions - "rogue protein", believed to be the cause of Mad Cow Disease,

INFLUENZA

BACTERIOPHAGE

H1N1

SMALLPOX