Viruses and HIV

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Viruses

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Is a Virus a Living Organism?

Chapter 1 – Properties of life

Cellular Respiration

Reproduction

Metabolism

Homeostasis

Heredity

Responsiveness

Growth and development

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Viruses are not living organisms

Viruses do not

Grow

Have homeostasis

Metabolize

Viruses do

Infect cells and use the cell to make more viruses

Cause disease in many organisms

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Parts of a Virion (a virus particle)

Nucleic Acid – RNA or DNA

Capsid – protein coat that surrounds the DNA or RNA in a virus

Lipid Membrane – a membrane around the capsid in many kinds of viruses; helps the virus enter cells (“enveloped” viruses; without the membrane, the virus is “naked”)

Made of proteins, lipids, and glycoproteins

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RNA or DNA?

Viruses with RNA

Human immunodeficiency virus (HIV)

Influenza viruses

Rabies

Viruses with DNA

Warts

Chickenpox

mononucleosis

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Virus Shapes

Helical

Rodlike with capsid proteins winding around the core in a spiral

Tobacco Mosaic Virus

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Virus Shapes

Polyhedral

Has many sides

Most polyhedral capsids have 20 sides and 12 corners

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Virus Shapes

Polyhedral capsid attached to a helical tail.

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How do viruses replicate?

2 methods of replication:

1. Lytic Cycle – the virus enters the cell, replicates itself hundreds of times, and then bursts out of the cell, destroying it.

2. Lysogenic Cycle – the virus DNA integrates with the host DNA and the host’s cell helps create more virus DNA. An environmental change may cause the virus to enter the Lytic Cycle.

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In the lytic cycle, the virus reproduces itself using the host cell's chemical machinery. The red spiral lines in the drawing indicate the virus's genetic material. The orange portion is the outer shell that protects it.

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