Chapter 1 – Properties of life
Growth and development
Viruses do not
Infect cells and use the cell to make more viruses
Cause disease in many organisms
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
Viruses with RNA
Human immunodeficiency virus (HIV)
Viruses with DNA
Rodlike with capsid proteins winding around the core in a spiral
Tobacco Mosaic Virus
Has many sides
Most polyhedral capsids have 20 sides and 12 corners
Polyhedral capsid attached to a helical tail.
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.
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.