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Lysogenic and Lytic Cycles

…When Viruses Attack

Learning Objectives

You should be able to describe lytic and lysogenic cycles of viruses

Viral Replication

• Viruses don’t reproduce on their own… they need cells!

• 2 different methods of viral replication– Lytic and Lysogenic

• Replication can involve both methods in separate phases (interchangeable)

Knock Knock….

• Before anything, viruses need to enter a cell

But how?1. Virus attaches itself to the

cell (specificity)2. Virus injects it’s DNA or RNA

into the cell

The Lytic Cycle

3. The viral DNA shuts down and takes over the host cell

4. The virus uses the materials of the host cell to make thousands of copies of its own protein coat and DNA (progeny produced)

5. The cell lyses (bursts) and releases hundreds of virus particles

The Lysogenic Cycle

3. The viral DNA is now known as a prophage

4. The prophage may remain as part of the host cell for many generations (no progeny produced)

5. Eventually the viral DNA removes itself from the DNA of the host cell and start reproducing viruses

6. The cell lyses (bursts) and releases hundreds of virus particles

Your Task…

• Visually show that you understand the difference between the lytic and lysogenic viral life cyclesAccurately portray the stages of the viral life

cycle – the process (both lytic and lysogenic)Compare and contrast the Lytic and

Lysogenic Cycles by drawing a Venn diagram on the back

• In the Lytic Cycle:• Viral DNA destroys Cell DNA, takes over cell functions and

destroys the cell.• The Virus replicates and produces progeny phages.• There are symptoms of viral infection.• Virulent viral infection takes place.

• In the Lysogenic Cycle:• Viral DNA merges with Cell DNA and does not destroy the

cell.• The Virus does not produce progeny.• There are no symptoms of viral infection.• Temperate viral replication takes place