Viral ReplicationSubtitle

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

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

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?

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

Bacteriophage Structure

• Icosohedral head• Contains the Viral

nucleic acid• Comprised of Protein

• Collar and Sheath (Tail) • Comprised of Protein• 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

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

The Lytic Cycle

▪ 5 Phases of the Lytic Cycle:1. Attachment2. Entry3. Replication4. Assembly5. Release

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)

2. Entry

▪ Bacteriophage releases an enzyme which weakens the cell wall, allowing for Nucleic acid to be inserted into the cell

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

4. Assembly

▪Viral genes are enclosed in the newly created viral capsids–Occurs mostly in cytoplasm, can occur in nucleus in eukaryotic organisms

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

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

Lysogenic Cycle

▪ Allows viruses to remain dormant for days, months, weeks, or even years.–“Temperate Viruses”▪ E.g. Human Immunodeficiancy Virus

▪ 4 stages1. Attachment2. Injection3. Integration4. Cell Multiplication

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

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

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.

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

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.

The Lysogenic Cycle

To Do Now

▪Work on 15.2 Review