2.
TEKS
4.C Students will…
Compare the structure of viruses to cells, describe viral reproduction, and describe the role of viruses in causing diseases such as HIV and influenza

3.
About Viruses
A virus is a non-cellular, non-living particle that invades and then multiplies inside a living cell
Smaller than the smallest living cell

4. About Viruses

5. About Viruses
The only way that viruses are like other organisms is that they can multiply – but only by getting energy from a host
A host is the living organism that the virus multiplies inside of
Viruses act like parasites – organisms that live on or in a host and cause it harm
Almost all viruses destroy their host cells

6. About Viruses All viruses have 2 basic parts
A capsid (protein coat) that protects the virus
An inner core of RNA or DNA that contains the instructions for making new viruses
Eukartyotic viruses usually have protective envelopes made from the host cell membrane

7. Virus Attachment
Each virus contains unique receptor proteins on its surface
The shape of the protein allows the virus to attach to certain cells in the host.
This “lock-and-key” system allows certain viruses to attach to specific host cells
Example: most cold viruses infect cells only in the nose and throats of humans

8. Virus Attachment

9. Bacteriophages Viruses that attack bacteria
T-phages are a specific class that have icosahedral heads, double-stranded DNA, and tails
Six spikes at the base of the contractile tail are used to attach to the host cell and inject the viral DNA

10. Bacteriophages

11. Retroviruses Contain RNA, not DNA
Contain an enzyme called reverse transcriptase that is injected into the cell along with the RNA
Reverse transcriptase causes synthesis of a complementary DNA molecule (cDNA) using the virus RNA as a template
Examples: HIV and influenza

12. Retroviruses

13. Lytic Cycle
Once inside a cell, the genetic material of the virus takes over many of the cell’s functions
The genetic material instructs the cell to reproduce the virus
Active viruses take over the cell functions immediately (lytic cycle)
Examples: colds and the flu
Takes a few days to feel sick

14. Lytic Cycle Five steps Attachment to the cell
Injection of viral genetic material (DNA or RNA)
Replication (biosynthesis) of new viral proteins and nucleic acids
Assembly (maturation) of the new viruses
Release of the new viruses into the environment (cell lyses)

15. Lytic Cycle

16. Lytic Cycle

17. Lysogenic Cycle
Some viruses have the ability to become dormant once they are inside the cell
They are called latent viruses
They can remain inactive for very long periods of time (years)
Later, they activate and enter the lytic cycle in response to some external signal
Examples: HIV and herpes

18. Lysogenic Cycle Seven steps Attachment to the cell
Injection of viral genetic material (DNA or RNA)
Virus genetic material integrates into host cell genetic materia to hide
An external signal activates the viral genetic material, which separates from the host cell genetic material
Replication (biosynthesis) of new viral proteins and nucleic acids
Assembly (maturation) of the new viruses
Release of the new viruses into the environment (cell lyses)

19. Lysogenic Cycle

20. Reproduction Comparison

21. Spreading of viruses Contact with a contaminated object
Droplets of moisture in the air (cold and flu viruses)
A bite from an infected animal (rabies)
Exchange of bodily fluids (ex: blood, semen, or vaginal secretions)
Vectors – an organism that transmits a disease without being affected by that disease (ex: mosquitos)

22. Treating Viruses No cures currently exist for viral diseases
The best treatment for a virus is a lot of rest, drinking plenty of fluids, and well-balanced meals
Over-the-counter medications can help to relieve symptoms
Some viruses can be treated with anti-viral drugs (anti-virals do NOT destroy the virus, simply inhibit development)
Antibiotics do NOT help in getting over a virus

23. Preventing Viral Disease
Vaccine: a substance that is introduced into the body which causes the body to produce chemicals that kill the virus (immune response)
Vaccines are made from either weakened or heat-killed viruses (attenuated)
The killed virus does not cause the viral disease, but it still causes the body to produce chemicals that destroy the virus
The body is able to “remember” the virus so that if it invades again it will be immediately destroyed

24. Influenza Virus (Flu)

25. Influenza

26. Influenza Retrovirus (RNA) Lytic
Spread via droplets (sneezing, coughing, etc)
Yearly vaccines due to the rate of mutation that changes the surface proteins of the virus (so they are no longer recognized by the immune system)

27. Human Immunodeficiency Virus (HIV)

28. HIV

29. HIV
Retrovirus (RNA)
Spreads through exchange of bodily fluids (blood; semen and vaginal secretions)
Lysogenic
Destroys helper T-cells of the immune system, which causes the immune system be unable to defend against pathogens
The virus is HIV; the disease is AIDS (autoimmune deficiency syndrome)