Viral reproduction

1. VIRAL REPRODUCTION

2. VIRAL REPRODUCTION
• Viruses are obligate intracellular parasites
• There are four stages of viral reproduction
1. Virus attaches to host cell and nucleic acid enters the cell
2. New components of the virus are synthesized using the cells
machinery
3. Virus components are assembled into new viruses
4. Viruses are released from the infected cell - Lysis
• Virus reproduction follows two possible pathways: The Lytic and
Lysogenic Cycles

4. LYTIC CYCLE
• Virus attacks cell and immediately takes over and produces more
viruses.
• Host cell bursts and viruses are released to infect other cells
• Symptoms of the viral disease occur right after infection
• All viruses go through the stages of lytic cycle
•Virulent: How quickly a virus replicates and is spread. More virulent
viruses tend to follow the lytic cycle

5. LYTIC CYCLE

6. BACTERIOPHAGE ANIMATION

7. FLU VIRUS ATTACK

8. LYSOGENIC CYCLE
• “Latent” cycle – allows virus to stay dormant in the
cell for several generations
•Only occurs with some viruses
• Virus attaches to cell and viral genetic material
enters the cell
• Viral DNA is incorporated with host DNA forming a
prophage (host DNA + virus DNA)
• Cells continues replicating as normal, producing
daughter cells each containing the prophage
• After many generations the virus is activated or
triggered and causes the disease by entering the
lytic cycle
• Triggers include time, other illness, stress etc.

9. LYTIC AND LYSOGENIC CYCLE

10. RETROVIRUS
• Most often DNA in a cell is transcribed into RNA which is translated
to form proteins ( DNA → RNA → Protein )
• Some viruses have RNA which they are able to convert into DNA for
insertion into the host genome using an enzyme carried by the
virus called reverse transcriptase
• Follows the lysogenic pathway before transcription to RNA and
translation to proteins
( RNA → DNA → RNA → Protein )
• Retroviruses mutate easily, therefore, hard to develop vaccines
• Most commonly infects animal cells
•Examples: HIV, Influenza