Viruses are non-living particles that can only reproduce inside living cells. They come in various shapes and sizes, with diameters ranging from 20-200 nanometers. Viruses are classified as parasites because they destroy the host cell during reproduction. They have either a protein coat containing genetic material or a protein coat surrounding an inner core and genetic material. Viruses attach and enter host cells using unique proteins that match receptors on certain host cell types. Once inside, the virus takes over the cell's functions to produce more viral proteins and genetic material, filling the cell until it bursts and releases new viruses. Some viruses remain dormant inside the host cell's DNA until certain triggers cause them to become active again.

1. Types of Microbes 1
VIRUSES

2. WHAT IS A VIRUS?
• A tiny, NON-LIVING particle that enters
and then reproduces inside a living cell.
• No organisms or cells are safe from
viruses. All can be infected by a virus.

3. Characteristics of Viruses
Viruses are NON-LIVING because:
1. They do not use their own energy to
grow or respond to the environment.
2. They cannot make food, eat food, or
produce waste.

4. Characteristics of Viruses
• Viruses can ONLY multiply inside of a
living cell.
• A HOST is an organism that provides a
source of energy for a virus or another
organism.
• A PARASITE is an organism that lives on
or in a host and causes it harm.

5. Characteristics of Viruses
• A virus is a parasite because almost all
viruses destroy the cell in which it
multiplies. It causes the host harm and
that is the definition of a parasite.

6. Virus Shapes
• Some of the shapes of viruses are:
round, rod-shaped, brick shaped, thread
shaped, bullet shaped, robot shaped.

7. Virus Shapes
Round
virus
Thread
virus
Rod
virus
Bullet
virus
Robot
virus
Called a
Bacteriophage

8. Virus Shapes
• A BACTERIOPHAGE is a virus that
infects bacteria. The word itself means
“bacteria eater”

9. Virus Sizes
• A virus is smaller than a cell (animal, plant
or bacteria)
• A NANOMETER (nm) = 1 billionth of a
meter.
• Diameter of the smallest virus = 20 nm
• Diameter of the largest virus = 200 nm

10. DIAMETER
Virus
The DIAMETER is the length of the
dashed red line.

12. Naming Viruses
Scientists name viruses a number of ways:
1. Named after the disease they cause
2. Named after the organisms they infect
3. Named after the place where it was first
found
4. Named after people

13. The Structure of Viruses
The 2 basic parts of a virus are:
1. PROTEIN COAT that protects the virus
2. INNER CORE made of genetic material
(DNA)
Some viruses are surrounded by an outer
membrane or envelope.

14. The Structure of Viruses
• The proteins in a virus help to invade the
host cell.
• Viruses only connect to certain host cells
because each virus has unique proteins
that allow it to attach to only certain host
cells. Its like a key (virus surface proteins)
that only fit a certain lock (host cell surface
proteins). Viruses won’t fit the lock on all
host cells, only a specific few.

15. The Structure of Viruses
KEY
LOCK
HOST
CELL
BRICK
SHAPED
VIRUS
Virus surface
protein
Host cell’s surface protein

16. The Structure of Viruses

17. HOW VIRUSES MULTIPLY
• Once a virus attaches to a host cell, it
enters the cell.
• Once inside the host cell, the virus’s
genetic material takes over the cell’s
functions. It tells the cell to produce the
virus’s proteins and genetic material so
that more viruses can be made.

18. Active Viruses
Once inside the host cell, an Active Virus starts
taking over:
1. The virus’s DNA takes over the cell’s
functions
2. The host cell makes more of the virus’s proteins
and DNA
3. New Viruses are made.
4. This continues over and over again until…. The cell
fills up with viruses and bursts.
5. Hundreds of new viruses are free to find more cells.

19. Active Virus

20. Hidden Viruses
Once inside the host cell, a Hidden virus hides for
awhile inside the host:
1. The virus’s DNA becomes part of the host cell’s
DNA
2. The virus hides out, not doing anything sometimes
for years.
3. Every time the host cell divides, the virus’s DNA is
copied along with the host cell’s DNA
4. Under certain circumstances, the virus’s DNA
becomes active.
5. Then the Hidden Virus becomes an Active Virus
and does the same thing an Active Virus does.
6. After an active period, it becomes a Hidden Virus
again.

21. Hidden Virus