PPT is about the virus reproduction, 2 main pathways

1. How viruses reproduce?
Chapter 6A

2. Learning objectives
• Understand what is meant by the terms lytic
and latency.

3. Virus life cycle
• Reproduce only in the host cells.
• Different ways of attacking to host cells:
bacteriophages inject their genome into the
host bacteria cells, but main part of the viral
material remains outside the bacterium. The
viral DNA forms a circle or plasmid within the
bacterium.

5. • Some viruses enter by endocytosis, host digests
the capsid, viral genetic material is released.
• Plant viruses use vectors(insects- aphids) to
penetrate cellulose cell wall.

6. • 2 different routes of infection:
1. Lysogenic pathway 2. Lytic pathway

7. Lysogenic pathway
• Many DNA viruses use this pathway.
• When enter to the host cell, do not cause the disease
immediately.
• The inserted DNA = provirus
• They repressor protein to stop the viral DNA transcription.
• Virus in this stage = latent.
• Under certain conditions viruses become active, repressor
protein decreases, they enter to lytic pathway, directly
become virulent.

9. Lytic pathway
• The viral genetic material is replicated independently
of the host DNA immediately after it enters the host.
• Mature viruses are made and eventually the host cell
bursts, releasing large numbers of new virus particles
to invade other cells.
• The virus is now disease-causing and the process of
replicating and killing cells is known as the lytic
pathway.

11. Retroviruses
• Ex.: HIV, the Rous sarcoma virus
• Make reverse transcription: RNA
to DNA by reverse transcriptase
enzyme in host cell’s cytoplasm.
• Viral DNA is inserted into the
host DNA in the nucleus.
• Later viral r. transcriptase
enzyme makes viral mRNA, and
viral genome RNA.
• Leave the host cell by exocytosis.

12. Viruses and disease
• Viruses cause the symptoms of disease by the
lysis of the host cells, by causing the host cells to
release their own lysosomes and digest
themselves from the inside or by the production
of toxins that inhibit cell metabolism.

13. • They are mostly specific, because of their markers.
• Ex.: adeno virus --- respiratory system
• Can cause different types of cancers: cervical cancer