 Simply: segments DNA or RNA wrapped in a protein coat  Not considered to be alive ◦ They can not reproduce themselves ◦ They rely on a host for reproduction

 Vary greatly in size and appearance ◦ Can range from 1.7 x m to 1x10 -6 m ◦ Comparable to the size of a hydrogen atom

 In 1933, a scientist tried to purify the tobacco mosiac virus  To great surprise, the virus ‘precipitated’ out of the solution in the form of crystals ◦ Only chemicals precipitate out of solution  Thus, viruses were thought to be chemical and not biological ◦ Containing the chemicals: RNA & Protein

 Same basic structure: ◦ A core of nucleic acid surrounded by a protein  Only a single type of nucleic acid: ◦ Linear ◦ Circular ◦ Double stranded ◦ Single stranded

 The protein coat is called a capsid ◦ Composed of one to many different protein molecules  Some animal viruses have another layer on top of the capsid ◦ Protein/lipid envelope

 Think of an infecting virus as a set of instructions ◦ Much like a cell is directed by its DNA  A new set of instructions can be added into the cell ◦ cause the cell to cease its original operation ◦ Devote all its energy to the new instructions  Viruses can reproduce only when they can utilize the host cell’s machinery ◦ They lack the ribosomes and enzymes necessary for replication

 Human  Immunodeficiency  Virus  RETROVIRUS ◦ Only contains RNA ◦ Uses a host cell enzyme called reverse transcriptase to create viral DNA from the RNA ◦ Viral DNA then gets incorporated into the host DNA

 HIV virus attaches to ‘helper T cells’ ◦ Helper T cells are a type of white blood cell that fight attack from incoming pathogens  HIV can not attach to any other type of cell (ex. muscle or skin)

 There are proteins on the outside of the HIV virus ◦ Ligands ◦ Antigens  Ligands are attracted to receptors on the host cell surface

 The process of HIV virus entering the host cell is called receptor-mediated endocytosis  Step 1: ligand and receptor bind  Step 2: HIV membrane and host cell membrane fuse  Step 3: HIV enters host cell

1. Once the viral RNA is inside of the host cell it encodes for the a specific, evil, protein called - REVERSE TRANSCRIPTASE 2. Reverse transcriptase creates viral DNA from RNA 3. The newly created viral DNA enters the host nucleus -becomes spliced into the host DNA

 The new DNA will be transcribed into mRNA  mRNA is translated into proteins ◦ Viral proteins will be produced to make new coat around viral RNA ◦ VIRUS IS REPLICATED!

 Final Step: ◦ mRNA translates HIV membrane proteins to become part of the host cell membrane ◦ When the HIV protein coat is complete it will bud off from the host cell  Leaving with a membrane coat from the host cell

 Challenges in containing HIV ◦ HIV has the ability to mutate to avoid detection  It is able to change the proteins on its outer membrane  These mutations make it difficult for the immune system to destroy the HIV-infected cells  HIV Medication ◦ There are several different classes of drugs that are used to interfere with the different HIV life cycle stages ◦ HAART = Highly Active AntiRetroviral Therapy  Combination of many drugs at once ◦ Serious/intolerable side effects

 Acquired  ImmunoDeficiency  Syndrome  First recognized in California and New York in 1979 as a immune system compromising disease  Homosexual men were having fevers, weight loss, and pneumonia!

 More and more cases started to occur all over the United States all with young, homosexual men  Number of individual diagnosed with AIDS in USA: ◦ 1980 – 200 ◦ 1981 – 800 ◦ 1982 – 3000 ◦ 1983 – 8000  In late 1980, two Danish men suffered from the same symptoms as the American individuals

 Soon, similar illnesses were popping up all over Europe ◦ ALL CASES could be traced back to the individuals in America  But who had it first? Who was ‘patient zero’?  Research traced all infections back to Gaetan Dugas ◦ French-Canadian Air Canada flight steward ◦ Infected 40 of the first 250 men diagnosed

 In 1982, a massive study was done by France  They found individual infected came from specific groups ◦ From America ◦ Traveled to America and had sexual relations ◦ Contaminated blood transfusion ◦ **Never traveled to America but still had AIDS  BUT, they had been to Africa

 Africa:  In 1970s, a Portuguese man lived in Africa as a truck driver ◦ He often traveled between Mozambique, Zaire, and Angola  He had a 3 year relationship with a Native women ◦ Developed pneunomia, fever, lost tremendous of weight ◦ Some of his bodily fluids were saved & frozen  10 years later they analyzed his fluid, and found it was HIV-2

 Now, the search was on in Africa for where the illness seemed to be coming from  The earliest known illness with similar symptoms was in 1959.

Natural-Transfer Theory  purposes that native hunters accidentally cut their hands when cutting up animals they had just caught  allowing the chimpanzee blood to enter the hunter’s blood  initially as these small tribes kept to themselves so the virus never spread  Africa soon became urbanized with highways and migrations allowing the virus to spread to more and populations... Eventually to America