How fast can you find your match?

1. How fast can you find your match? • You picked up a cut piece of construction paper on your way in. • Someone in this classroom has your match! • They should fit together like puzzle pieces. • You have 30 seconds to find your match! Once you find each other, stand next to each other until the time is up. • First pair to find each other gets a prize!

2. Viral Infections • Once a virus enters a host cell, one of two processes will occur: • Lysogenic Cycle • Lytic Cycle

3. The Lytic Cycle

4. The Lytic Cycle • Viral nucleic acid is injected into the host cell. • Host cell begins to make mRNA from the viral DNA. • Viral proteins shut down the host cell’s regular functions. • Cell is used to make thousands of viruses. • Host cell bursts (lyses) & releases viruses to infect other cells. This is a cell lysing with new viruses. Viruses that cause a host cell to burst are referred to as virulent viruses.

6. The Lysogenic Cycle

7. The Lysogenic Cycle • Viral nucleic acid is injected into the host cell. • DNA is integrated (joined) into the host DNA. • Host cell continues dividing with the virus DNA. • Eventually, the viral DNA can be triggered to enter the Lytic Cycle! Cold sores are caused by a strain of Herpes virus. This virus enters the Lysogenic Cycle, but can enter the Lytic Cycle if your immune system is weakened. This is when you get a cold sore! Viruses that use the lysogenic cycle are referred to as temperate viruses.

9. Which cycle will spread viral DNA to other cells? • Lytic Cycle • Lysogenic Cycle • Both Both!

10. Which cycle can cause disease? • Lytic Cycle • Lysogenic Cycle • Both Both!

11. Which cycle stops the host cell’s functions? • Lytic Cycle • Lysogenic Cycle • Both The Lytic Cycle!

12. Which cycle is more sneaky? • Lytic Cycle • Lysogenic Cycle • Both The Lysogenic Cycle! Even if the cold sore goes away, the virus never does…

13. What is the correct sequence of events of the Lytic Cycle? Try to do this without looking at your notes. Use logic! • Injection, Transcription, Translation, Assembly, Lysis • Injection, Assembly, Translation, Transcription, Lysis • Lysis, Assembly, Injection, Transcription, Translation • Assembly, Transcription, Translation, Lysis, Injection A. Injection, Transcription, Translation, Assembly, Lysis

14. DNA vs. RNA Viruses • DNA viruses don’t mutate frequently, because they utilize the host cell’s DNA polymerase. Remember! DNA polymerase can proofread & correct errors during DNA replication. • This is why you only need a vaccine for a DNA virus once! (smallpox, HPV)

15. DNA vs. RNA Viruses • RNA viruses have high mutation rates, because when the cell copies RNA for new viruses, the enzyme cannot fix mutations. • You need new vaccines for RNA viruses every year, because they evolve so quickly! (the flu)

16. RNA Viruses AKA Retroviruses • RNA viruses do not have built in proofreading, so they mutate & evolve QUICKLY! • Some cancers & AIDS are caused by retroviruses! • We know RNA is made from DNA, but not the other way around. How can a virus that contains RNA take over a host cell’s DNA? Human Immunodeficiency Virus

17. Retroviruses • Retroviruses also need to inject reverse transcriptase. • Enzyme that makes double-stranded DNA copy of viral RNA to incorporate into the host cell’s DNA • Lysogenic cycle then proceeds normally

19. Before you leave… • Answer the following question on the back of your handout: Which cycle do you consider to be more dangerous? Lytic or Lysogenic? Defend your answer!