Viruses Virus: A biological particle composed of nucleic acid and protein pathogen: anything that causes sickness or disease

Viral Structure Figure 19-9 Virus Structures Tobacco Mosaic T4 Bacteriophage Influenza Virus RNA Capsid proteins Head/Capsid Tail sheath DNA RNA Tail fiber RNA Capsid Surface proteins Membrane envelope

Are viruses alive? No Yes Not made of cells or organelles Can’t reproduce on own (without a cell) Don’t metabolize energy Don’t perform cellular processes Reproduce Have nucleic acid Adapt to surroundings Have organization

All Have: 1) Capsid: coat of protein that surrounds nucleic acid 2) Nucleic Acid: RNA or DNA Some Have: Tail Fibers: Used for attachment (not legs) Shapes vary Virus Parts

The Lytic Cycle 1st Step: Attachment Virus attaches to a cell receptor No attachment = No infection

The Lytic Cycle 2nd Step: Entry Virus enzyme weakens cell membrane Genetic material (DNA or RNA) enters host cell

The Lytic Cycle 3rd Step: Replication Virus DNA/RNA makes virus proteins by transcription/ translation

The Lytic Cycle 4th Step: Assembly New virus proteins are assembled into new viruses

The Lytic Cycle 5th Step: Release Virus enzyme causes host to burst Viruses are released to find new host…Cycle repeats

The Lysogenic Cycle 1) Attachment: Virus attaches to host cell Host cell DNA Pro-phage 2) Entry: Virus nucleic acid enter the cell, but combines with host cell DNA.

The host cell divides by mitosis, making a copy of the prophage each time. Two infected cells.

Two cells divide by mitosis to make 4 infected cells. Pro-phage Pro-phage

Four infected cells divide by mitosis to make 8…and so on….

Virus DNA eventually becomes active and starts to create viruses following the stages of the lytic cycle. All infected cells burst, releasing many more viruses to restart the cycle.

Lytic and Lysogenic Infections

Disease caused by specific viruses Common Diseases Caused by Viruses Disease caused by specific viruses Section 19-3 Type of Virus Nucleic Acid Disease Oncogenic viruses Retrovirus Adenoviruses Herpes viruses Pox viruses DNA RNA Cancer Cancer, HIV Respiratory infections Chickenpox Smallpox

Vaccines Injection of a weakened or dead pathogen Causes an immune response Allows your body to make antibodies and memory cells against the disease