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Non-Living Viruses Infectious AgentsWhat are they? How do they work? Where do they come from? And… What good are they? Non-viral Infectious Agents • Viroids- The smallest known particle that can replicate. – Single Strand of RNA – Disrupt plant cell metabolism – Can destroy entire crops • Prions – Abnormal forms of proteins that clump together inside cells. – Clumping eventually kills the cell – Example • Mad Cow Disease 2 • • • • • Overview of Viruses Nonliving Composed of Nucleic acid and protein Cause many diseases Virology – Study of Viruses Comparison of Viruses and Cells below Char. Of Life Virus Cell Growth Homeostasis No No Yes Yes Metabolism No Yes Mutation Yes Yes Nucleic acid DNA or RNA DNA Reproduction Only within host cell Structure Nucleic acid core, protein covering, some have envelope Independently by cell division Cytoplasm, cell membrane, etc.. Characteristics of Viruses • 2 essential features • 1. Nucleic Acid – May be DNA or RNA – Helical, closed loop, or long strand • 2. Protein Coat – called CAPSID • Some have ENVELOPE – Ex. Influenza, chickepox, herpes simplex, HIV • VIRAL SHAPE – Icosahedron – 20 triangular faces • Ex.) herpes, chickenpox, polio – Helix – Coiled spring • EX.) Rabies, measles, tobacco mosaic • Bacteriophages: like tiny little syringes that inject DNA from the virus into the cell 6 Lytic Cycle Bacteriophage 1. Attachment- Virus finds host cell Host cell DNA 2. Entry- Viral DNA injected into host 5. Lysis & Releaseviruses burst out of host (dies); Find new host 3. Replication- Host makes viral DNA & parts 4. Assembly- New viruses made Here is a non-enveloped bacteria virus inserting it’s DNA into a bacterial cell. Some virus are pushed out by the cell, taking some of the cell membrane with them. 10 Lysogenic Cycle • After Step #2 of the Lytic Cycle, the Virus may become Dormant and enter into the Lysogenic cycle • Dormant- non-active time of virus – Host is infected, but doesn’t know it – Ex: Herpes (cold sores) Person doesn’t have them all the time, but has “outbreaks” throughout year – Ex: HIV Mono Lysogenic Cycle From Step #2 Lytic cycle, enters Lysogenic cycle here 5. Cell enters back into Lytic Cycle- Assemble, Lysis & Release Many cell divisions 4. Cell Multiplication – Ho replicates with viral DNA 2. Entry- Viral DNA injected into host Provirus 3. Integration - Viral DNA becomes part of host DNA Classification of Viruses 1. By Shape 2. Host type 3. function Retroviruses attack a certain way. Animal viruses DNA viruses attack another way. Plant viruses Bacteria viruses Viruses and Human Disease • Control and Prevention of spread. – Vaccination & Antiviral drugs • Ex.) chickenpox vaccine, AZT, Acyclovir, protease inhibitors. • Emerging Viruses – exist in isolated habitats – Do not usually infect humans unless environmental conditions favor contact. • Several viruses are now linked to cancers such as leukemia, liver cancer, Burkitt’s lymphoma, cervical cancer. English physician and scientist from Berkeley, Gloucestershire, who was the pioneer of smallpox vaccine • Cowpox and smallpox are closely related, but cowpox is a much less serious disease than smallpox. • Jenner noticed milkmaids were immune to smallpox. • He used puss from a cowpox blister to inocculate an 8 year old boy • He called his method “vaccination,” from the Latin word vacca, or cow, and today we use vaccination to refer to immunization against any disease. • A vaccine contains a killed/weakened part of a germ. • When a person receives a vaccine, the body reacts by making protective antibodies. Wendell M. Stanley • Wendell M. Stanley crystallized and described the molecular structure of the tobacco mosaic virus. PAPOVAVIRUSES: Tumor causing viruses Most common: Human papillomavirus (HPV) (warts) ADENOVIRUSES: causes respiratory issues and pink eye HERPESVIRUSES: easily transmitted by direct contact with a lesion or the body fluid of an infected individual POXVIRUSES PICORNAVIRUSES The name is derived from pico, meaning small, and RNA, referring to the ribonucleic acid genome, so "picorna-virus" literally means small RNA virus. Ranges from the common cold to polio! MYXOVIRUSES RHABDOVIRUSES RETROVIRUSES: genes are encoded in RNA instead of DNA Here is a classic picture of HIV viral progeny being released from the surface of a T- cell. Notice the membrane coating they receive. Ebola Virus • Some therapies that have worked have been when patients receive blood from convalescent patients 26 28