Cells vs. Viruses

By Cassie Scott

What are they?

What is the difference between a cell and a virus? Which characteristics of life do cells have that viruses do not? What is the difference between their reproduction cycles? You will discover all this and more in my flyer below!
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Virus Examples

An example of a lytic cycle virus would be the common cold and an example of a lysogenic cycle virus would be herpes.

CHARACTERISTICS of LIFE

The Characteristics of Life:

1) Living things grow and develop

2) Living things have DNA

3) Living things respond to the environment

4) Living things are made of one or more cells

5) Living things reproduce

6) Living things maintain homeostasis

7) Living things obtain and use material and energy

8) Living things evolve

9) Living things are organized

Which Characteristics of Life do Viruses Have?

Viruses have a few of the characteristics of life. Viruses have DNA to help give them internal instruction and direction. Viruses reproduce using either the lytic or lysogenic cycle (pictured above) within a cell. The last characteristic of life viruses have is the fact that they evolve. This is why a person gets a new flu shot each year! Viruses constantly evolve to be able to keep infecting cells that have no antibodies for that virus yet.

QUESTIONS

Describe the typical structure of a virus. What is a virus made of? What biomolecules would you find in a virus?

A typical virus contains DNA or RNA surrounded by a protein coat called a capsid. Some viruses even have a lipid membrane covering the protein coat called an envelope. Viruses with RNA are called retroviruses. Viruses are not considered living due to the fact that they aren't made of cellulose. The biomolecules you would find in a virus are nucleic acids, proteins, and in some viruses, lipids. Nucleic acids are the DNA or RNA you would find controlling all viruses. Proteins are found in the capsid surrounding the DNA or RNA. Some viruses have lipids in the envelope covering the protein coat.

Discuss the different ways viruses gain entry into a cell.

There are several ways a virus enters a cell which depends on which type of virus it is and the cell it is entering (animal, plant, fungi). These are membrane fusion, endocytosis, and genetic injection. Membrane fusion works when the viruse's envelope "blends" with the cellular membrane and injects its contents into the cell. Viruses with no viral envelope enter during the cell's endocytosis, tricking the cell into letting it in and infecting the cell. Genetic injection works when the virus attaches itself to the cell's surface and injects just the genome into the cell, leaving the rest on the surface. This usually happens with bacteriophages.

Explain why the Ebola virus would not infect a tobacco plant.

The ebola virus would not infect a tobacco plant because the ebola virus can only infect human cells. Viruses are very specific with which types of cells they infect and cannot just go and infect any type of cell on any organism.

Name five viruses and the type of cell that they attack.

Human metapneumovirus - Animal cells

Herpes B virus - Animal cells

Measles virus - Animal cells

Tobacco necrosis virus - Plant cells

Flu virus - Animal cells

You have been diagnosed with the flu. Explain why a doctor will not provide you with a prescription for antibiotics in order to cure your infection.

A doctor could not cure the flu with antibiotics because the flu is a virus and antibiotics kill bacteria. Antibiotics would do nothing to a virus, they only kill bacteria.

How is it that a person can be infected with a virus such as HIV and not exhibit symptoms?

It is because HIV just weakens the immune system. If a person comes in contact with no bacteria or illnesses, it doesn't matter if they have no immune system. That is why it can take a few weeks for any symptoms to show up.