The Structure of Viruses

CHARACTERISTICS IN COMMON THAT YOU NEED TO UNDERSTAND. ALL LIVING THINGS HAVE 5 CHARACTERISTICS IN COMMON THAT YOU NEED TO UNDERSTAND.

1. All living things are made of cells A cell is the building block of all life. It is the smallest structure that can be classified as living.

2. All living things metabolize nutrients Metabolism is the set of chemical reactions that occur inside of living cells. Glucose metabolism

3. All living things reproduce themselves

DNA stands for deoxyribonucleic acid 4. All living things contain genetic material in the form of DNA. DNA stands for deoxyribonucleic acid A DNA molecule is a long repeating chain of nucleotides.

5. All living things maintain a steady balance of water, nutrients and energy known as homeostasis. Photo by W.J.Pilsak

Viruses are NOT made of cells and viruses CANNOT metabolize nutrients. Computer reconstruction by Graham Colm Viruses are NOT considered to be alive because they cannot do all 5 of these things. Viruses are NOT made of cells and viruses CANNOT metabolize nutrients.

Image of smallpox patient courtesy of CDC/ World Health Organization; Stanley O. Foster M.D., M.P.H. Viruses do not have a metabolism to keep balanced, and they actually disrupt the homeostasis of organisms as they reproduce themselves inside of their host’s cells.

Genetic Material (DNA or RNA) Viruses do contain genetic material. This is usually in the form of DNA, but some viruses actually carry their genetic material in the form of RNA.

Viruses also reproduce themselves, but as we will learn, they can only do this with the help of a host cell.

How do viruses compare to eukaryotic and prokaryotic cells in size? The Size of Viruses How do viruses compare to eukaryotic and prokaryotic cells in size? Click on the image to travel to the web site.

The Structure of Viruses All viruses contain genetic material in the form of DNA or RNA. Genetic Material (DNA or RNA)

The Structure of Viruses This genetic material is stored inside of a protein shell. This protein shell is known as the capsid.

The Structure of Viruses Viral capsids can take a few different shapes. Most are helical or icosohedral. Some viruses known as bacteriophages have very complex structures. Image by Adenosine Image by Arionfx

The Structure of Viruses Chicken Pox Virus with Envelope Some viruses are even surrounded by a layer of cell membrane known as the envelope. Viral envelopes are pieces of membrane taken directly from the host cell that made the virus. Chicken Pox Virus with Envelope

The Structure of Viruses Viruses often have protein surface markers surrounding their capsid. These proteins are critical to how the virus attaches to its host cell before an infection. Computer reconstruction by Graham Colm

These surface markers are usually specific to the receptor proteins of a particular cell type. Because of this, specific viruses only attach to the few cells that have these specific receptors.

Virtually all viruses do is reproduce themselves Virtually all viruses do is reproduce themselves. To do this, they must utilize a host cell. The reason that this makes you sick is because in the process of reproducing themselves, viruses destroy the host cells that they use.

Discuss the following question with your classmates about what you learned today. 1. What are 2 reasons that viruses are considered to be nonliving? They are not made of cells and they cannot metabolize nutrients. enzyme

Discuss the following question with your classmates about what you learned today. 2. What 2 things do viruses and cells have in common? They both have genetic material and they both reproduce themselves.

Discuss the following question with your classmates about what you learned today. 3. What do viruses need in order to replicate? Viruses need a host cell in order to replicate. This can be any type of cell: animal, plant, protist, fungus or bacteria. H.I.V. uses T Helper cells as host cells.

Discuss the following question with your classmates about what you learned today. 4. What do you call the protein coating around a virus? The protein coat is called the capsid. ?

Discuss the following question with your classmates about what you learned today. 5. What do viruses do that is harmful to host organisms? They destroy the host’s cells at they reproduce.