4. Virus

BIOGEOSPHERE Bilingual Biology and Geology I.E.S. "J.S.Elcano (Sanlúcar Bda.)

Unit 10: The simplest living beings 1 2 3 4

4. Viruses

Viruses are the smallest microorganisms.

To see them, an optic microscope is not enough. We need a much more powerful electronic microscope.

They have a very simple structure:

- A capsid. It is a protein coat

that can have different shapes

(helical, icosahedral, etc.)

- A genome. It is a nucleic acid (DNA or RNA).

It’s the genetic material of the virus.

Some of them, have also an envelope. That is a cellular membrane that comes from the previous infected cell.

They cannot be considered living beings, because they don’t perform all the vital functions. Viruses don’t feed, don’t move by themselves, and don’t interact with their environment. They only can reproduce, but they must do it infecting a host cell like a parasite.

A virus attaches itself to a cell. Then, it invades the cell and puts its genetic material into the cell. This genetic material contains instructions, which the cell must follow. The instructions are very simple: make more viruses just like the invader.

The infected cell begins to make viruses, and cannot stop. Sometimes the new viruses fill the cell and make it explode. Other times the virus stays inside the cell for some time.

Viruses can infect every type of cells and all of them are pathogens that provoke diseases in the infected organism.

Some examples of human viral diseases are cold, influenza, SIDA, measles, mumps, poliomyelitis, viral meningitis, etc.

Animation: What are viruses? (University of Manchester)

READING ACTIVITIES

After reading the text, copy and answer the following questions into your notebook:

Remember: you must make complete sentences.

4.1. Answer the following questions about viruses:

a. Why viruses are not considered living beings?

b. Is there any beneficial virus? Why?

c. How many parts can we distinguish in a virus?

4.2. Listen to the description of viruses and complete the text

with the missing words.

Viruses

They are not made up of ……………………….., which is why they are not considered living things and are therefore not classified in any ………………………. They infect a host cell in order to ………………………. All viruses are ………………………………….. and are only visible through a powerful electronic …………………………….

They have a simple structure that consists of:

- A polyhedral or helical ………………………. A viral envelope, similar to the cell membrane, encloses the capsid in some viruses.

- ………………………….. material which information to reproduce.

Viruses can only replicate inside a ………………………… cell. When the virus has reproduced in the host cell, the newly reproduced viruses leave the cell and …………………….. new host cells. A virus outside a host cell is a ……………………………. particle.