Transcript Viruses

The Immune System
• Objectives:
• 1) Know the difference between
viruses and bacteria.
• 2) Know the different ways that
bacteria and viruses attack the
body.
Viruses
The Structure of Viruses
How Viruses cause Disease
Virus Size
Viral Structure
• Viruses differ widely
in structure and size.
• General structure of a
virus is genetic
material, DNA or
RNA surrounded by a
protein coat called a
capsid.
How viruses enter cells
• Viruses have to bind to
receptors on the outside of
cells.
• Cells won’t knowingly let
viruses in, so the virus
tricks the cell into letting
it in by using receptors
that are meant to let in
something else. (Nutrients,
for example)
Viruses also inject their
genetic material into the cell.
• Here a
bacteriophage (a
virus that infect
bacteria) injects
its genetic
material into a
bacteria.
If viruses infect cells then how is
it that all cells are not infected?
• Viruses only infect certain types of cells. This is
known as their host range.
• Viruses can only get into cells that have the
proper receptors on the outside.
Viral Infections
Viruses need to infect cells to
reproduce.
• Lytic Infection: A virus enters a cell, uses the
cell’s “machinery” to make copies of itself and
then causes the cell to burst (Lyse)
• Lysogenic Infection: The virus’s genetic
material (DNA) bonds with the cell’s DNA and
replicates along with the cell until it enters the
lytic cycle. The viral DNA bonded in the cell’s
DNA is a prophage
Which infection do you think is
worse?
Are viruses alive?
• What are the traits of
living things?
• How many of these
traits do viruses have?
• Do you think viruses
are alive? Why or
Why not?
Characteristics of Living Things
•
•
•
•
•
•
•
•
•
Pg 18 in your text, Living Things:
1) Are based on Universal Genetic Code
2) Grow and develop
3) Respond to their environment
4) Reproduce (sexual/asexual)
5) Maintain homeostasis
6) Have a metabolism
7) Are made up of cells
8) As a group, evolve.
Are viruses alive?
• Think about what
traits viruses
have, do you
think viruses have
enough of the
traits of living
things to be
considered alive?