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 10-8m to 1x10-6m

◦ 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