Presentation on theme: " Viruses- particles of nucleic acid, protein and sometimes lipids Most viruses are so small, they can only be seen through a powerful electron microscope."— Presentation transcript:
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
They reproduce at a good rate, but only in living host cells. They can mutate.
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.
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 - 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
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
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
1. What are the two ways the two ways viruses cause infections?