1. Viral Replication
Subtitle

2. First a Review of Where we have gotten so far
Taxonomy and Scientific Naming
Viruses
Characterizing and Grouping Viruses based on structure
Nucleotides and Proteins
Envelope and glycoproteins
Icosohedral, spherical, complex, helical shapes
Microscopy and Scientific Drawings

3. First a Review of Virus Structure and Scientific Drawings
Provide a Scientific Drawing of a virus using the following labels:
Nucleic Acid
Capsid
Glycoprotein
Envelope

4. Viral Replication Consider what we already know/ have learned about:
We know viruses cannot reproduce independently – they need a host in order to replicate
Viruses contain DNA and RNA , and are comprised of proteins
How can Viruses utilize host cells for their own replication purposes?

5. The Bacteriophage A Virus which infects bacteria
With the ability of scientists to more easily study bacteria, bacteriophages provided a window into how Viral diseases replicate
Used to help develop gene therapy

6. Bacteriophage Structure
Icosohedral head
Contains the Viral nucleic acid
Comprised of Protein
Collar and Sheath (Tail)
Along with head makes up the capsid of the virus
Act like “syringe” – inject viral nucleic acid into the host
Tail fibers
Assist in virus attachment to cell

7. Viral Replication
Two Basic Types of Viral Replication that have been studied
Lytic Cycle
What makes viruses “viral” – cause diseases
Lysogenic Cycle
What makes a virus “temperate” – Remains dormant in host cells for extended periods of time

8. 5 Phases of the Lytic Cycle: 1. Attachment 2. Entry 3. Replication
4. Assembly
5. Release

9. 1. Attachment
Begins by virus attaching to host cell using tail fibres to attach to receptor sites on cell surface
Receptor Sites: Areas on the cell which the virus can recognize and bind to
Receptor sites are important, because if a cell doesn’t have them, viruses move to the next group of cells which do
This is how Viruses gain specificity (e.g. Hepatitis Virus only infects liver cells)

10. 2. Entry
Bacteriophage releases an enzyme which weakens the cell wall, allowing for Nucleic acid to be inserted into the cell

11. How the Viral DNA is replicated Utilizes our DNA  Protein process
3. Replication
How the Viral DNA is replicated
Utilizes our DNA  Protein process
Transcribe Viral DNA into Viral RNA, which is then translated into Viral proteins
Viral proteins form the capsid

12. Viral genes are enclosed in the newly created viral capsids
4. Assembly
Viral genes are enclosed in the newly created viral capsids
Occurs mostly in cytoplasm, can occur in nucleus in eukaryotic organisms

13. 5. Release
Bacteriophage releases enzyme which disintegrates host cells
Cell disintegration is known as LYSIS
Viruses with envelopes force themselves through the cell and “borrow” a piece of the cell as th envelope

14. To Do Now:
Using the sheet in front of you to show the Lytic Cycle in action:
Cut and paste the different stages in order of the cycle
Provide a brief description of each stage

16. 4 stages Lysogenic Cycle Attachment Injection Integration
Allows viruses to remain dormant for days, months, weeks, or even years.
“Temperate Viruses”
E.g. Human Immunodeficiancy Virus
4 stages
Attachment
Injection
Integration
Cell Multiplication

17. 1. Attachment and 2. Injection
Work in the same way as the Lytic Cycle – Tail fibers find receptor sites, and inject nucleic acid into the host cell

18. 3. Integration
After the bacteriophage has injected it’s DNA into the host cell, it integrates its DNA into the host cell’s DNA. The Viral DNA is now part of the host cells genome, and can be replicated, transcribed and translated the same way it would for the host cell’s DNA.
The Bacteriophage DNA molecule that integrates into the host genome is known as the PROPHAGE

19. 4. Replication
Once integrated into the host cells genome, the Viral DNA will replicate, and become part of cell division in the same way that our DNA does (2 copies – one per each cell in cell division)
Our cells keep replicating and replicating, containing the viral DNA each time it does.

20. Replication cont’d
Lysogenic viruses are said to be “temperate” – remain dormant, do not cause diseases.
Radiaton, or certain chemicals however can cause a temperate virus to break its lysogenic cycle, and become part of the lytic cycle (causes disease – Virulent)
It will produce viral RNA/DNA and protein, assemble into new viruses and lyse the cells, spreading the virus throughout the host

21. Lysogenic Puzzle
Like the Lytic Cycle, please cut and paste the different stages of the lysogenic cycle onto a piece of paper, and provide a brief description of each stage.
Do not worry about “e” – It is just the stage when the Lysogenic cycle becomes the Lytic Cycle. Where the Viral DNA no longer becomes part of the host genome and begins the replication step of the Lytic Cycle.

22. The Lysogenic Cycle

24. To Do Now
Work on 15.2 Review