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19-2 Viruses. By: Katelyn, Rose and Ashley . What is a Virus?. Viruses- particles of nucleic acid, protein and sometimes lipids Most viruses are so small, they can only be seen through a powerful electron microscope.
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19-2 Viruses By: Katelyn, Rose and Ashley
What is a Virus? • Viruses- particles of nucleic acid, protein and sometimes lipids • Most viruses are so small, they can only be seen through a powerful electron microscope. • A typical virus is composed of a core of DNA or RNA surrounded by a protein coat. • The more complex the virus is the more genes it contains • They enter a living cell and once inside, use machinery of infected cell to produce more viruses
Living characteristics of viruses: • They reproduce at a good rate, but only in living host cells. • They can mutate.
Nonliving characteristics of viruses Nonliving characteristics of viruses • They are acellular, that is, they contain no cytoplasm or cellular organelles. • viruses don't grow and divide. Instead, new viral components are synthesized and assembled within the infected host cell. • They possess DNA or RNA but never both.
What is a Capsid? • Capsid- a protein coat • The capsid enable’s host cells to enter the virus • The capsid proteins “trick” the virus by binding the surface of the cell allowing the capsid to come inside the cell • The cell transcribes and translates the viral genetic information into viral capsid proteins. • Sometimes it causes the host cell to make copies of the virus, and it causes the host cell to be destroyed
Bacteriophages- viruses that infect bacteria • Once the virus is inside the host cell two different process may occur • In a lytic infection, a virus enters a cell and replicates itself and causes the cell to burst. • In the lysogenic infection the virus replicates itself in a way that doesn’t kill the host cell immediately.
Prophage and Viral Infections Prophage - viral DNA that is embedded in the host cell’s DNA Prophage may remain part of the DNA for many generations before being active A virus may not always stay in the prophage Eventually one factor will activate the DNA of a prophage causing it to remove itself form the host cell DNA and direct the synthesis of a new virus particles
What are Retroviruses? • Retroviruses- viruses that contain RNA as their genetic information • When retroviruses infect a cell they produce a DNA copy of their RNA • The DNA is then inserted into the DNA of the host cell
Viruses and Living Cells • In order for a virus to grow it must infect a living cell • Viruses are parasites • After infecting living cells viruses can reproduce • Viruses are borderline of living and none living things • Viruses are smaller and simpler than cells
Review : • What are the two ways the two ways viruses cause infections?
Answer: 1.Lysogenic and lytic
Review: 2. What are typical viruses composed of?
Answer: • Core of DNA or RNA surrounded by protein coat
Review: • What is the viruses protein coat called?
Answer: • capsid
Review: • How do viruses “reproduce”?
Answer: • They enter a living cell and once inside, use machinery of infected cell to produce more viruses