Biology - Viruses

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Viruses

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Non-cellular particle made up of genetic material + protein that can invade living cells

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Structure of a Virus

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Capsid, bacteriophage

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Capsid

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Protein coat protecting nucleic acid core. Protects the genes inside core.

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Bacteriophage

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Head region composed of a capsid, nucleic acid core, and tail.

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How do viruses reproduce

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They need to invade or infect a living host cell.

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Method of replication

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Uses host materials to make thousands of copies of its own protein coat and DNA, soon the host cell is filled with viral DNA

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Methods of infection

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Lytic and Lysogenic Cycles

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Lytic Infection

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Infected cell lyses (bursts) and releases hundreds of virus particles infecting other cells.

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Lytic Cycle

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1. Bacteriophage attaches to bacterium's cell wall

2. Injects genetic material into bacterium

3. Takes over bacterium's metabolism causing synthesis of new bacteriophage proteins/nucleic acids

4. Proteins/nucleic acids assemble into complete bacteriophage

5. Enzymes lyses bacterium's cell wall releasing bacteriophages.

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Lysogenic Infection

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Virus does not reproduce and lyse host cell right away.

DNA enters cell and inserted into the DNA of the host cell instead. The viral DNA inside the host cell (called PROPHAGE) may remain part of host DNA for many generations.

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Prophage

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Viral DNA inside of host cell.

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Retroviruses

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Contain RNA as genetic information, and creates a DNA copy of its RNA to insert inside host cell (like a prophage)

Goes from RNA to DNA (backwards), responsible for types of cancer in animals/humans, AIDS.

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Parasites

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Organism that depends entirely upon another living organism for its harmful existence.