Viruses are microscopic particles that contain genetic material but are not living organisms. They invade host cells to reproduce and are made up of a protein coat that surrounds a core of nucleic acid. To reproduce, viruses must recognize, attach to, and inject their genetic material into a living host cell, where they assemble new viral particles that cause the host cell to burst and release the new viruses. There are two main types of viral reproduction: lytic viruses immediately replicate and kill the host cell, while lysogenic viruses integrate their DNA into the host's genome and remain dormant until activating to produce new viruses.

1. What is a virus?
•Microscopic particles
(microbe) that invade the
cells of living organisms.

2. Viral Characteristics…
Viruses are not living
organisms!
Living Characteristics
Contain genetic
information –DNA or RNA
Heredity- do pass
genetic information to
next generation
Can reproduce
Non-Living
Characteristics
Not cells- can’t make
proteins.
Can’t make or use
energy.
Can’t survive or
reproduce without a host.

3. What does a virus look like?
• Viruses have many different shapes
and sizes, but all viruses are smaller
than bacteria cells.

5. Basic Structure of Virus
• Core-
nucleic acid (DNA or RNA)
• Capsid-
protein coat surrounds core

6. In order to exist and
reproduce,
a virus must invade
a living cell.
This living cell is referred
to as a host.

7. Viral Reproduction
Steps of viral reproduction:
• Recognition
• Attachment
• Injection
• Assembly
• Lysis

12. Lytic Viruses
• This type of virus replicates immediately and kills the
host cell.
• Virus enters host, replicates, causes host to burst= lysis.

13. Lysogenic Virus
Virus does NOT kill host
immediately.
Viral nucleic acid “fuses” with
the host cell nucleic acid.
Lysogenic viruses have a
“dormant” period.
Results in many cells being
“infected.”

14. Lysogenic Virus
PROPHAGE
(VIRAL DNA)