what is a virus

We have all heard of viruses. The flu, the common cold, and many other diseases are caused by viruses. But what is a virus? Do you think viruses are living? Which domain do they belong to? Bacteria? Archaea? Eukarya?

are viruses alive

The answer is actually no. A virus is essentially DNA or RNA surrounded by a coat of protein ( Figure 1.1). It is not made of a cell, and cannot maintain a stable internal environment ( homeostasis). Recall that a cell is the basic unit of living organisms. So if a virus is not made of at least one cell, can it be living? Viruses also cannot reproduce on their ownthey need to infect a host cell to reproduce. So a virus is very different from any of the organisms that fall into the three domains of life. Though viruses are not considered living, they share two important traits with living organisms. They have genetic material like all cells do (though they are not made of cells), and they can evolve. The genetic material of a virus can change (mutate), altering the traits of the virus. As the process of evolution has resulted in all life on the planet today, the classification of viruses has been controversial. It calls into question the very definition of life.



Viruses infect a variety of organisms, including plants, animals, and bacteria, injecting its genetic material into a cell of the host organism. Once inside the host cell, they use the cells own ATP (energy), ribosomes, enzymes, and other cellular parts to make copies of themselves. The host cell makes a copy of the viral DNA and produces viral proteins. These are then packaged into new viruses. So viruses cannot replicate or reproduce on their own; they rely on a host cell to make additional viruses.

viruses and human disease

Viruses cause many human diseases. In addition to the flu and the common cold, viruses cause rabies, diarrheal diseases, AIDS, cold sores, and many other diseases ( Figure 1.2). Viral diseases range from mild to fatal. Cold sores are caused by a herpes virus.


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a virus causes the common cold.

-->  a. true

b. false

viruses can evolve.

-->  a. true

b. false

what does a virus use from a host cell to replicate?

a) atp, dna, rna

-->  b) atp, ribosomes, enzymes

c) dna, ribosomes, enzymes

d) atp, ribosomes, dna

viruses cause which of the following human diseases?

a) the flu, aids and bubonic plague

-->  b) the flu, aids, and cold sores

c) aids, cold sores and athletes foot

d) the flu, aids and athletes foot

what does it mean for a virus to infect a cell?

a) the virus lands on the outside of the cell then completely enters the cell.

-->  b) the virus lands on the outside of the cell and injects its genetic material into

c) the virus lands on the outside of the cell and injects its proteins into the cell.

d) the virus enters the cell through the outer cell membrane.

which domain do viruses belong to?

a) bacteria

b) archaea

c) eukarya

-->  d) viruses do not belong to any domain.

which is the best definition of a virus?

-->  a) a non-living particle consisting of rna or dna surrounded by a protein coat.

b) a non-living particle consisting of rna or dna surrounded by a dna coat.

c) a living particle consisting of protein surrounded by a dna or rna coat.

d) a living particle consisting of rna or dna surrounded by a protein coat

diagram questions

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