1. Viruses

2. Viruses
What is a virus?
Sub-microscopic particle consisting of a single nucleic acid surrounded by a protein coat and capable of replication only within the living cells of bacteria, animals or plants.
MOST scientists would say that virus is a lifeless particle that is only capable of reproducing within living cells.
Does this by injecting is self into a host
Wait!!!!! Lifeless?
As mentioned most scientists do not consider viruses to be living organisms, but this is debatable!

3. What are the characteristics of a living organism?
Living things….
Are made up of cells
Grow and develop
Reproduce
Respond to their environment
Adapt to their environment
Obtain and use energy
Produce wastes

4. Size of a Virus Viruses are so small they are measured in units called
nanometers (nm)
10-9m – 1-billionth of a
meter.
Their sizes can range from
20nm to 400nm in diameter.
Viruses are so small that you require an electron microscope
About 5000 influenza viruses could fit on the head of a pin!

5. Shape of a virus
The shape of the virus is determined by the type and arrangement of the proteins in the capsid.
Capsid – the protein shell of a virus
The most common shapes are:
Spherical – HIV
Helical/Cylindrical – The tobacco mosaic virus
Polyhedral (20 triangular sides) – Polio virus
Complex, has a polyhedral head attached to a protein tail and several tail fibers – T4 virus

6. Structure Far less complex than a living organism
A virus consist of the following:
Nucleic Acid Core - Set of genetic instructions, either DNA or RNA, either single-stranded or double-stranded
Capsid – Protective protein coat surrounding the DNA or RNA
Accounts for 95% of the total virus and gives the virus its shape
Lipid membrane - Surrounds the protein coat (found only in some viruses, including influenza; these types of viruses are called enveloped viruses
as opposed to naked viruses)
Receptor sites – help the virus
attach to the host cell

7. Classifying Viruses
How to tell them apart

8. viruses
Viruses do not contain the chemical machinery (enzymes) needed to carry out the chemical reactions for life.
Viruses carry only one or two enzymes that decode their genetic instruct