VirusesI. What is a Virus

a. You’ve probably had the flu _________________at some time during your life.b. Nonliving particles called ________________ cause influenza.c. Viruses are composed of _________________________ enclosed in a protein

coat and are smaller than the smallest ______________________.d. Most biologists consider viruses to be ______________________ because they

don’t exhibit all the criteria for life.e. They don’t carry out

i. ___________________ii. ___________________

iii. ___________________ f. All viruses can do is ____________________—make copies of themselves—and

they can’t even do that without the help of living cells.g. A cell in which a virus replicates is called the _____________________.h. Viruses, such as _______________ viruses and ______________, were named

after the diseases they cause.i. Other viruses were named for the ____________________________they infect.j. Today, most viruses are given a _____________name ending in the word “virus”

and a _________________ name.k. However, sometimes scientists use ____________________to distinguish among

similar viruses that infect the same host.l. A virus that infects a bacterium is called a ____________________________or

phage for short.

II. Discovery of Virusesa. In 1892, __________________________ demonstrated that the cause of tobacco

mosaic disease was found in the liquid extracted from infected plants.b. In 1897, ___________________________ suggested that tiny particles in the

juice caused the disease; he named these particles ______________, after the Latin word for “poison.”

c. In 1935, ______________________isolated crystals of tobacco mosaic virus.

III. Virus Structure and Compositiona. A virus has an inner core of nucleic acid, either ________ or _________, and an

outer protein coat called a __________________.b. Some relatively large viruses, such as human flu viruses, may have an additional

layer, called an ________________, surrounding their capsids.c. Some viruses have only four genes, while others have hundreds

d. The tobacco mosaic virus has a long, narrow helical shape.

i.e. The arrangement of proteins in the capsid of a virus determines the virus’s

___________.f. Polyhedral viruses resemble small _________________.g. The protein arrangement also plays a role in determining what cell can be

____________________and ________________the virus infects the cell.

IV. Attachment to a host cella. Before a virus can replicate, it must ______________a host cell.b. A virus _________________and ____________ to a host cell when one of its

proteins interlocks with a molecular shape that is the ____________________ on the host cell’s plasma membrane

c. A protein in the tail fibers of the bacteriophage T4 recognizes and attaches the T4 to its bacterial host cell.

i.d. In other viruses, the attachment protein is in the ____________ or in the

envelopee. Each virus has a ___________________________attachment protein. Therefore,

each virus can usually attach to only a _______ kinds of cells.f. In general, viruses are ______________________, and some also are cell-type

specific. For example, polio viruses normally infect only intestinal and nerve cells.

g. The species specific characteristic of viruses is significant for controlling the ______________ of viral diseases.

V. Viral Infectiona. Viruses use their genetic information to reproduce inside living cells.b. some viruses replicate immediately.

i. _____________________________c. Other viruses initially persist in an inactive state within the host.

i. _____________________________

VI. Lytic Infectiona. The virus __________________ DNA into a bacteriumb. Viral genes are ____________________ by the host cell.c. The bacterium makes new viral ___________ and nucleic acid.d. The proteins and nucleic acids __________________ into new viruses.e. Viral enzymes __________ the bacterium’s cell wall. The new viruses ________

i.

ii. Analogy1. The host cell’s DNA is chopped up2. Virus uses host cell to make viral DNA and viral proteins.3. The host cell bursts, releasing hundreds of virus particles.

VII. Lysogenic Infectiona. The virus _________________DNA into a bacteriumb. The viral DNA _______________ itself into the bacterial chromosome.c. The _______________ may replicate with the bacterium for many generations.d. The prophage can _________ the bacterial chromosome and _________a lytic

cycle.

i.

VIII. An RNA Virus : The Common Colda. About _____________ of viruses contain RNA rather than DNA. In humans,

RNA viruses cause a wide range of infectionsi. ________________________

ii. ________________________iii. ________________________

b. Certain kinds of cancer also begin with an infection by viral RNA.c. Once the cold virus has penetrated the host’s cells, it uses the host’s cellular

machinery to replicate itself

IX. An RNA Virus : HIVa. Acquired immune deficiency syndrome (AIDS) is caused by an RNA virus

called human immunodeficiency virus (HIV). b. HIV belongs to a group of RNA viruses that are called retroviruses. The genetic

information of a retrovirus is copied from RNA to DNA instead of from DNA to RNA.

c. HIV makes a DNA copy of itself that inserts into the host’s DNA. There, it may remain inactive for many cell cycles.

Cytoplasm

DNA

Cytoplasm

.

X. Viruses and Cells

XI. Viral Disease Mechanisms