1. Viruses

2. What to Know: Learning Objectives
Overview:
What are some basic facts about viruses?
Structure:
What are the shapes?
Reproduction:
What is the lytic & lysogenic pathways?
Infection:
How do they get into cells and then get reproduced?
Describe a few common or well-known virus.
AIDS, the common cold, hepatitis, influenza
What are viroids & prions?

3. Viruses Infectious particles (not cells)
Contain Genetic information and protein coat (capsid)
Some may contain RNA
Grouping is determined by the type of nucleic acid (DNA or RNA)
Typically named after the disease they cause or the tissues they infect

4. Virus Structure Simple virus structure
Genetics… this is the direction to make more virus
Surrounded by proteins (capsid)
May or may not have an additional covering (envelope)
Each have their own form but can be categorized:
Helical
Polyhedral
Enveloped
Other.

5. Helical
Polyhedral
Enveloped
Others

6. Viruses: Living or Not? Considered to be non-living (debated)
Does not meet all of the characteristics of life
Living
Non-Living
-Contains genetic material (RNA/DNA)
-Reproduce (in host)
-Has organization
-Do not have cells
-Do not respond to stimuli
-Do not use energy
-Do not grow & develop
-Cannot reproduce on their own

7. Viral Reproduction Viruses must have a living host cell to reproduce
Example: Bacteriophages infect bacteria
Insert their genetic information inside the host cell and use the host cell to make more virus particles

8. Viral Replication Lytic cycle Viral DNA is injected into host cell
Contains instructions needed to make more viruses
Host cell replicates viral DNA and makes the viral capsids (protein coats)
New viruses are assembled inside host cell
Cell bursts open releasing new viruses

9. Lytic Cycle

10. Viral Replication Lysogenic cycle
Viral DNA is injected into the host cell
Viral DNA inserts itself into the host’s DNA
Remains inactive for days, months, or years
As the cell reproduces, more cells are produced that have the viral DNA in them
Eventually, when the conditions are favorable (like when your immune system is weakened) the virus will enter the lytic cycle

11. Lysogenic Cycle

12. Lytic Pathway Lysogenic Pathway
A Virus particle binds, injects genetic material.
Lytic Pathway
A1 Viral DNA is inserted into host chromosome by
viral enzyme action.
Lysogenic Pathway
E Lysis of host cell
lets new virus particles escape.
A2 Chromosome and integrated viral DNA are replicated.
B Host replicates viral genetic material, builds viral proteins.
A3 Cell
divides; recombinant DNA in each daughter cell.
D Accessory parts are attached to viral coat.
C Viral proteins self-assemble into a coat around viral DNA.
A4 Viral enzyme excises viral DNA from chromosome.
Figure 21.4
Pathways in the multiplication cycle of a bacteriophage.

14. Transmission of Viral Disease
Virus are pathogenic and carcinogenic.
They cannot reproduce unless they attack another cell.
Once in the cell the have a tendency to cause irreparable damage that can lead to cancer.
HPV & Cervical cancer
Possible ways to become infected are
Bites
Physical contact
Body fluid
Mother to child
Contact in the air
Sexual contact

15. Video clip Write 5 facts from the video
Get into groups, divide the chapter up into sections, read through and gather information, answer the questions.

16. Here's a better, longer answer than the one in the video
Here's a better, longer answer than the one in the video. First, some new viruses get caught in mucus and other fluids inside your body and are destroyed. Other viruses get expelled in coughs and sneezes. Second, lots of those new viruses are lemons. They don't work that well. Some don't have the right "keys" to invade healthy cells so they can't spread the infection. And third, as the animation shows, your immune system is busy attacking the viruses whenever and wherever possible.