1. VIRUSES
Viruses – are segments of nucleic acids contained in a protein coat; they are not cells; they are smaller than prokaryotes and range in size from 20nm to 250 nm

2. Is A Virus Alive? NO, viruses do not have all the properties of life, so biologists do not consider them to be living; viruses do not grow, do not have homeostasis, and do not metabolize
Viruses are pathogens – agents that cause disease; they replicate by infecting cells and using the cell to make more viruses

3. Viral Structure:
capsid– the virus protein coat; may contain either RNA or DNA, but not both
envelope – viral membrane; it helps the virus enter cells; it consists of protein, lipids, and glycoproteins
nucleic acid – DNA or RNA
RNA viruses: HIV (Human
Immunodeficiency Virus), Influenza, rabies
DNA viruses: warts, chickenpox,
mononucleosis

4. Viral Structure
Glycoprotein
used to attach to surface of cell

5. Viral Shapes
Rod
Helix
Polyhedral
Sphere
Complex

6. Viral Reproduction:
Viruses lack enzymes necessary for metabolism and have no structures to make proteins.
Viruses must rely on living cells (host cells) for replication.
*How do viruses enter a cell?
Plant cell – through tiny tears in the cell wall
Animal cell - by endocytosis
Bacteria – it punches a hole in the bacterial wall and injects its DNA into the cell

7. Once inside a cell, the virus can take one of two different paths: the lytic cycle or the lysogenic cycle.
lytic cycle – is the cycle of viral infection, replication, and cell destruction
lysogenic cycle – the viral gene is inserted into the host chromosome and whenever the cell divides, the viral gene is copied resulting in 2 infected host cells; a change in the environment can cause the viral gene to begin the lytic cycle
ex: cold sores/fever blisters – the virus hides deep in the nerves of the face; when conditions in the body became favorable, such as when a person is under stress, the virus begins to cause tissue damage

8. Lytic vs. Lysogenic Cycle