Name: _____________________________________________________

AIDS: Evolution of an Epidemic

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Viral Infection Mechanism

Part 1: The virus
The animation begins inside a ___________________ containing a sample of a ___________________. Here we see a schematic of the virus with its receptors, envelope, protein shell, and _______________________. As the camera zooms out, we will see a drop of the solution being deposited on a petri dish containing cultured of __________________________.

Part 2: The cell monolayer
As the camera zooms into the petri dish, we can see that it is covered with a thin layer of cultured cells ____________________ to infection by the virus. The cell membrane, cytoplasm, and ______________________ of a single cell are labeled.

Part 3: The cell receptors
Increased magnification reveals ___________________________ on the surface of the cell. These are receptors that are used by cells to communicate with each other, as well as for other cellular functions. The virus ______________________________ of these proteins to bind to the membrane of the cell. In the next part of the animation, we will see how receptors on the surface of the viral envelope bind to the cell's own receptors to allow _____________________________________ to occur.

Part 4: Fusion with the cell's plasma membrane
The fusion of the cell membrane with the viral envelope allows the viral protein shell and ___________________________ to be released into the ________________________________ of the cell. The viral receptor proteins remain on the surface of the infected cell's __________________________________ and will later be incorporated into the envelopes of newly formed viruses. The contents of the virus are delivered into the cell's ___________________________, where the viral protein shell is disassembled. This step frees the viral genome. It enters the cell _______________________, where it is ___________________________. Only a few proteins remain associated with the viral genome to permit its passage through the nuclear membrane.

Part 5: Replication of the viral genome
Once inside the host cell, different types of viruses have different mechanisms for ______________________ their genomes. DNA viruses generally replicate their DNA in the nucleus of the host cell, while RNA viruses generally replicate their RNA in the _____________________________. Here, the example shows a DNA virus whose genome enters the host cell's nucleus and replicates by taking advantage of the host cell's DNA replication machinery. Newly ______________________________ viral DNA becomes the genome of progeny viruses, but it is also used to make mRNAs that code for viral _____________________. The mRNAs enter the cytoplasm and use the host cell's protein synthesis ________________________________ to make viral proteins. The replicated viral genome leaves the host cell's nucleus and reenters the cytoplasm, where it is ____________________________ into the protein shell made from newly synthesized viral proteins.

Part 6: Viral budding
The newly formed viruses now return to the host cell's plasma ________________________________, which contains thousands of copies of newly synthesized viral receptor proteins. Viral ____________________________is the process by which the virus acquires a new envelope from the plasma membrane of the host cell. Now the host cell is covered with thousands of copies of the original virus ready to be released and ____________________________more cells.
The last part of the animation shows the progeny viruses _______________________________ other cells in the petri dish. As each cell dies, it turns black. Over the course of several ____________________________, dying cells spread out in a circle across the surface of the dish.

Viral Infection Background

Unlike bacteria, viruses are ______________________________ (not cellular). A virus particle contains only one type of nucleic acid, either ___________________________________, which is sometimes surrounded by a protein coat. Sometimes the coat is further encased in a membrane called an ________________________________. Viruses can only reproduce by using the cellular machinery of ________________________________________________. Viral reproduction involves the replication of a virus's genetic material, either RNA or DNA, and the synthesis of proteins that either make up the virus (structural proteins) or that are needed to perform certain functions (such as replication).
In the process of ___________________________________, the genetic information encoded in the viral DNA is copied or transcribed into a complementary base sequence of RNA. The virus then uses the cellular machinery to __________________________________ specific proteins from the RNA through the process of translation.
For an RNA virus, the genetic material is already in a form that can be translated into _____________________________.