The lytic cycle involves a virus infecting a host cell, using its cellular machinery to replicate itself, and then causing the cell to burst and release new virus particles. It follows 5 steps - attachment, penetration, synthesis of viral components, assembly of new viruses, and release of viruses. The lysogenic cycle involves the viral DNA integrating into the host genome without killing the cell. The viral DNA is passed on to daughter cells until it is triggered to enter the lytic cycle.

1. LYTIC & LYSOGENIC CYCLE

2. LYTIC CYCLE:
• It is commonly referred as the reproductive cycle of the
bacteriophage.
• A virus undergoes lytic and lysogenic cycles to reproduce.
• It is relatively more common, wherein a virus infects a host cell,
use its metabolism to multiply and destroy the cell completely.

3. STEPS OF THE LYTIC CYCLE
1.ATTACHMENT 2.PENETRATION
3.SYNTHESIS 4.ASSEMBLY 5.RELEASE

4. 1.ATTACHMENT
• A virus requires a host cell for multiplication.
• In a first step, a virus attaches itself onto the host cell.
• The virus may attach itself on the receptor of the cell, or simply
any other part on its surface.
• In some cases, a small part of the viruses attaches to the host,
instead of the virus itself.

5. 2.PENETRATION
• Once attached, the virus the gains access to the cell body by
breaking through the cell’s plasma membrane.
• In some cases, the cell wall tail fibres of the virus and enzymes
released by it help in breaking through the same.
• The virus then release its genetic material into the host cell.
• The cell is now said to be infected.

6. 3.SEIZURE OF CELL MECHANISM
• The infected DNA or RNA then hijacks the host cell’s genetic
material and mangles with its gene expression.
If DNA is injected:
• The virus DNA transcribes itself into mRNA molecules.
• This molecules can control the host’s ribosome.
• Thus, the virus gains control of the host cell’s mechanism.

7.  If RNA is injected:
• An enzyme called reverse transcriptase transcribes the virus’s
RNA into DNA.
• This DNA is again transcribed into mRNA molecules.
• Thus it take over the mechanism.
• The virus takes over the cell machinery to produce multiple viral
components.
• Simply put the virus infects the host to produce more virus parts.
• Also virus puts the host nucleotides to work and replicate its own
genetic material.

8. 4.VIRUS MULTIPLICATION AND CELL DESTRUCTION
• Now that the genetic material as well as viral parts are replicated,
the host metabolism assembles new viruses from scratch.
• The capsid are assembled, followed by the genetic material in the
head and finally the tail fibre is attached to the end portion.
• Eventually, the host cell is filled with viruses.
• Once the assembly is completed, the virus releases an enzyme that
disintegrates the cell wall from within.
• Thus, destructing the host cell.
• The virus are individual and free now.

10. LYSOGENIC CYCLE:
1.PENETR
ATION
2.REPLICATION
OF GENETIC
MATERIAL
3.CELL
DIVISION

11. 1.PENETRATION:
• Once the virus’s genetic material is inserted, it attaches itself to
that of the host’s.
• Some viruses may not immediately start multiplying or replicating
after infecting the cell.
• In case it does not start replicating, the virus is said to be dormant.
• The virus genetic material is known as Prophage, while it is in the
dormant stage.

12. 2.REPLICATION OF GENETIC MATERIAL
• Thereafter, the cell will fall back into its regular metabolic
activities and eventually prepare for cell division.
• The genetic material or nucleic acid replicates, and the nucleus
divided into two parts.
• Each part having the same genetic information.

13. 3.CELL DIVISION
• The cell organelles will be replicated (in some cells) followed by
division of the cell body, resulting in two daughter cells.
• Each having virus’s genetic information incorporated to their
genetic material.
• The cells have utter normally until the virus is triggered.
• This daughter cells carrying the viral genetic material are known
as Lysogenic cycle

14. REFERENCE:
1.DAVID FREIFELDER,
TEXTBOOK OF
MOLECULAR BIOLOGY,
PAGE NO: 553-560.
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15. THANK YOU
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