Viruses: What is a Virus?
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Viruses: What is a Virus?
A virus is a tiny, nonliving particle that enters and then reproduces inside a living cell.
No organisms are from viruses.
Characteristics of Viruses:
Most biologists today consider viruses to be because viruses do not have all the characteristics essential for life.
Viruses are cells and do not use their own energy to grow or to respond to their surroundings.
Viruses also cannot make food, take in food, or produce wastes.
The only way in which viruses are like organisms is that they are able to .
Although viruses can multiply, they do so differently than organisms. Viruses can multiply only when they are inside a living cell .
The organism that a virus enters and multiplies inside is called a .
A host is an organism that provides a source of for a virus or another organism.
A virus acts like a , an organism that lives on or in a host and causes it harm.
Almost all viruses
destroy the cells in which they multiply. Virus Shapes:
Viruses vary widely in .
Some viruses are , while some are rod-shaped.
Other viruses are shaped like bricks, , or bullets.
There are even viruses that have complex, shapes, such as the bacteriophage.
A is a virus that infects bacteria. In fact, its name means “bacteria eater.”
Just as viruses vary in shape, they also vary in .
Viruses are smaller than cells and cannot be seen with the you use in school.
Viruses are so small that they are measured in units called (nm), which is one billionth of a meter.
The Structure of a Virus
All viruses have two basic parts: a protein coat that protects the virus and an inner core made of genetic material .
A virus’s genetic material contains the for making new viruses.
Like keys, a virus’s proteins fit only into certain “ ,” or proteins, on the surface of a host’s cells.
After a virus to a host cell, it enters the cell.
Once inside a cell, a virus’s genetic material takes over many of the cell’s functions.
It instructs the cell to produce the virus’s proteins and genetic material.
These proteins and genetic material then assemble into new viruses.
Some viruses take over cell functions . Other viruses wait for a while.
immediately (video clip)
After entering a cell, an active virus immediately goes into action.
The virus’s genetic material takes over cell functions, and the cell begins to reproduce.
When it is full of new viruses, the host cell bursts open, releasing of new viruses as it dies.
Other viruses do not immediately become active. Instead, they “ ” for a while.
After a virus enters a host cell, its genetic material becomes part of the cell’s genetic material.
The virus does not appear to affect the cell’s functions and may stay in this state for years.
Each time the host cell divides, the virus’s genetic material is along with the host’s genetic material.
Then, under certain conditions, the virus’s genetic material becomes active.
It takes over the cell’s in much the same way that active viruses do.
Soon, the cell is full of new viruses and open.
The virus that causes cold is an example of a hidden virus.
It can remain inactive for months or inside nerve cells in the face.
While hidden, the virus causes no .
What is a virus?
A nonliving particle that invades a cell and reproduces.
What basic structures do all viruses share?
An inner core of genetic material surrounded by a protein outer coat.
Scientists hypothesize that viruses could not have existed on Earth before organisms appeared. Use what you know about viruses to support this hypothesis…
Viruses cannot exist without organisms because to reproduce they must have a host cell they can invade.
Compare and contrast active and hidden viruses.
Both are viruses that are going to invade and reproduce in a host cell. The difference is that an active virus immediately takes over the cell and a hidden virus stays “hidden” and waits a while to take over.
Do you think that the Influenza virus is an active or hidden virus? Explain your reasoning.
- Active because soon after “catching” it from someone, the symptoms appear.