1. Viral Infectious Cycles – Lytic (pkt pg 12) AND Lysogenic (pkt pg 13)
Virus -
protein coat (capsid)
nucleic acid
(DNA or RNA)
attachment proteins

2. Lytic Cycle Step 1 – Adsorption Step 2 – Entry
Attachment proteins “connect” by fitting the shape of plasma membrane receptor proteins; “tricking” the cell
Step 2 – Entry
Can be EITHER the whole virus OR the nucleic acid injected
Virus is invading the host cell

3. Lytic Cycle
Virus immediately takes over metabolic activity of the cell (host)
Cell no longer functions normally
Organism feels “sick”
Homeostasis is NOT being maintained

4. Lytic Cycle Step 3 – Replication Protein synthesis at ribosomes
Use AA’s from host cell
Nucleic acid synthesis
Use host’s nucleotides
Controlled by VIRAL DNA or RNA
Uses host cell’s - nutrients, enzymes,
and ATP

5. Lytic Cycle Step 4 – Assembly Step 5 – Release
Put viruses together by inserting nucleic acid into protein coat
Step 5 – Release
Lysis – cell is destroyed by being broken open to release newly formed viruses (100’s or even 1000’s)
Can now infect new cells => Cycle

6. Lytic Cycle - Summary Host gets “sick” right away
DNA or RNA activated right away
Short (usually days)
Uses cell’s metabolism
Examples: flu, cold, H1N1

7. Lysogenic Cycle Step 1 – Attachment and Entry
Same as Steps 1 and 2 of Lytic Cycle
Step 1 – Adsorption
Attachment proteins “connect” by fitting the shape of plasma membrane receptor proteins; “tricking” the cell
Step 2 – Entry
Can be EITHER the whole virus OR the nucleic acid injected
Virus is invading the host cell

8. Provirus – host DNA with viral DNA Host – bacteria (prokaryote)
Lysogenic Cycle
Step 2 – formation of provirus
Viral DNA becomes incorporated into the host cell’s DNA
Host does NOT feel “sick”
Cell continues to function NORMALLY
Homeostasis is NOT disrupted YET!!!
DNA
Provirus – host DNA with viral DNA
Host – bacteria (prokaryote)

9. Lysogenic Cycle Step 3 – Mitosis/Cell division
Host grows and functions NORMALLY
Host undergoes mitosis
Host unknowingly copies the viral DNA along with it’s own and passes them to daughter cells – infecting other cells
Host STILL NOT “SICK”!!!

10. Lysogenic Cycle HOST is sick!!!!!
Steps 4 through 6 – Viral DNA becomes “activated” and enters the Lytic Cycle
Viral DNA takes over metabolism of host cell
Viral genes and proteins are synthesized
Viruses are assembled
Lysis occurs and viruses are released
HOST is sick!!!!!

11. Lysogenic Cycle Summary
Host is able to function normally (for a while) – may not know they are infected
Viral RNA will first be converted to DNA
Provirus
Uses cells metabolism to do mitosis
Longer & more complicated
MORE DANGEROUS
Examples: HIV, cold sores