VIRAL REPRODUCTION

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 cell2. New components of the virus are synthesized using the cells

machinery3. Virus components are assembled into new viruses4. Viruses are released from the infected cell - Lysis• Virus reproduction follows two possible pathways: The Lytic and Lysogenic Cycles

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

LYTIC CYCLE

BACTERIOPHAGE ANIMATION

FLU VIRUS ATTACK

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.

LYTIC AND LYSOGENIC CYCLE

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