Complete – “Characteristics of Viruses” before continuing with the notes

What are they?-submicroscopic infectious particles witha) Protein coat or capsidb) Nucleic acid (i.e. genetic material – DNA OR RNA)-much smaller than bacteria-size = 10 – 250 nm(1 nm = 10-9 m)

Diversity-infect every kingdom-most are species specific-come in many shapes and sizes-naturally occurring always cause disease -scientists investigating use of viruses for genetic engineering and gene therapy

-Mutations are common and frequent(Mutation = small change in DNA)-mutations lead to “new strains”)-may become more virulent-may jump the species barrier

Protection = Vaccinations-vaccination = dead or very weakened strain of virus is introduced into your body.-specific antibodies are made by your body to attack the virus-then, if you ever contact a live strain, your body will attack the virus quickly as your body has already produced antibodies to fight the virus

E. bola

HIV

Influenza

Measles

a. Viruses have genetic material (DNA or RNA, not both!!)

b. Viruses can mutate

2. Nonliving characteristics:

a. Viruses do not need energy – they do not grow or produce waste

b. They do not have any cellular features – no cell membrane, cell wall or organelles

c. They can only reproduce in a HOST cell

Relative Sizes and Detection Devices

http://learn.genetics.utah.edu/content/cells/scale/

Note: 1 mm = 0.001 meters (1000 mm = 1 m) (1 mm = 1000 microns)1 um = 0.000 001 m (1 000 000 micrometers(um) = 1 m) bacteria = 5 – 10 um1 nm = 0.000 000 001 m (1, 000, 000, 000 nanometers(nm) = 1 m) viruses = 10-250 nm

If a cell = the size of classroom, an average virus = size of a softball.

Are Viruses:

• Eukaryotic or Prokaryotic? NEITHER

• Unicellular or multicellular? NEITHER

• Autotrophic or heterotrophic? NEITHER

• Asexual or sexual? NEITHER

• Made of a cell membrane or cell wall? HAVE NEITHER

Viruses are infectious agents with both living and nonliving characteristics.

1. Living Characteristics:

aa.

What is a Virus?

A) Virus Structure Is made up of 2 – 3 parts:

1.Nucleic acid core (= DNA or RNA)2.Surrounded by a protein coat called a CAPSID

Capsomere = small sub units that make up the capsid The shape of the capsid can vary in shape & size

3. Some (not all) have a membrane coat = an ENVELOPE that surrounds the protein coat or capsid. Enveloped viruses are common in Animal viruses, not in plant viruses

B) What do viruses infect? Animals e.g. HIV virus causes AIDS; Influenza virus causes the fluPlantse.g. Tobacco mosaic virusBacteria

Bacteriophages (= phage for short) = viruses that infect bacteria = the most complex structure

Viral Specificity:Due to a viruses shape, size and structure, specific viruses can only infect specific organisms.

Some viruses can only infect humans Some viruses only infect mammals Some viruses only infect coldblooded animals, or plants or bacteria

This is called VIRAL SPECIFICITY. The specificity of a virus for a host occurs due to the proteins or spikes on the virus capsid “fit” and bind to receptors on the cell’s membrane, like a lock and key. If it fits, it tricks the cell and lets the virus in. If the virus doesn’t fit, it cannot enter the cell.

Structure Notes:- Nucleic acid (DNA or RNA)

is contained inside the capsid.

- Protein tail (sheath & tail fibres) used to attach to bacterium cell

HEAD

TAIL

C. How do viruses infect cells? And Reproduce?

A virus is like a parasite that infects and using living cells to reproduce in. Viruses inject their DNA or RNA into a living cell. Once inside the cell, one of two things can happen now:

o LYTIC CYCLE – viral genetic material takes over the cell, immediately making new viruses within the host cell and eventually kills (lyses) the cell OR

o LYSOGENIC CYCLE – the virus becomes DORMANT. The viral genetic material become PART of the cell’s genome, and is reproduced every time the cell reproduces.

Let’s look at both processes in more detail now. See

Viral Life Cycle Drawings

Viral Reproduction – PPT notes

Homework: Read pages 482-483 and answer the following questions.

1. A retrovirus contains RNA as its genetic material instead of DNA. Explain what happenswhen a retrovirus infects a host cell.

2. Where does the name retrovirus come from?

3. What well know disease is caused by a retrovirus?

4. Using the information in figure 19-11 and in note, explain why scientists do not consider viruses to

be living things.

Read page 490 and answer the following questions.1. Explain what a viroid is. How is it similar to a virus?

2. What is a prion? How does it cause disease?

Virus Evolution: Would viruses have evolved before or after living cells? Why?

Virus Evolution:1. Viruses may be non-cellular ancestors2. Viruses may have had cellular ancestors , but have evolved/adapted to become parasites3. Viruses may be fragments of other cells

Final Notes:• Almost all viruses cause diseases,• Scientists are using viruses for research and ways to help humans.

- Since viruses can transport DNA and RNA into cells, scientists are looking to viruses as a mechanism to do GeneTherapy

- In Gene Therapy, viral genetic material is replaced with new DNA