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This text explores the nature of viruses, detailing their structure, including the capsid that facilitates entry into host cells and the viral genetic material (DNA or RNA). It distinguishes between the living and nonliving characteristics of viruses, as well as the processes of lytic and lysogenic infections. The role of bacteriophages and retroviruses is also highlighted, explaining how they replicate by hijacking the host cell's machinery. A comprehensive overview that encapsulates current knowledge of viral biology.
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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
