Biology Sylvia S. Mader Michael Windelspecht Chapter 20 Viruses, Bacteria, and Archaea Lecture Outline See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 1

20.1 Viruses, Viroids, and Prions Biology, 9th ed,Sylvia Mader 20.1 Viruses, Viroids, and Prions Chapter 21 Viruses, Bacteria & Archaea Virus Associated with a number of plant, animal, and human diseases noncellular May have a DNA or RNA genome. Invention of the electron microscope allowed these infectious agents to be first seen French chemist Louis Pasteur suggested that something smaller than a bacterium was the cause of rabies

Viruses, Viroids, and Prions Biology, 9th ed,Sylvia Mader Chapter 21 Viruses, Viroids, and Prions Viruses, Bacteria & Archaea Viral Structure and Classification: Viruses are characterized by Size and shape 10–400 nm in diameter Type of nucleic acid core Single stranded or double stranded? DNA or RNA? Capsid or no capsid (outer layer composed of protein subunits): Some are enveloped by membrane Others “naked”

Viruses, Viroids, and Prions Biology, 9th ed,Sylvia Mader Chapter 21 Viruses, Viroids, and Prions Viruses, Bacteria & Archaea Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Capsid (protein) Covering Envelope (not found in all viruses) Virus particle Nucleic acid molecule (DNA or RNA) Inner core Various proteins (enzymes)

Viruses, Viroids, and Prions Biology, 9th ed,Sylvia Mader Viruses, Viroids, and Prions Chapter 21 Viruses, Bacteria & Archaea Viruses: Are obligate intracellular parasites Are either active or inactive, instead of living or non-living Can be cultured only inside living cells Chicken egg Tissue culture Three hypotheses about viral origin and evolution Proteins and nucleic acids, organic molecules in viruses, evolved and viruses may have arisen from these two basic polymers when cells did. Viruses may have evolved backwards from living cells. Viruses degenerated from living cells.

Viruses, Viroids, and Prions Biology, 9th ed,Sylvia Mader Viruses, Viroids, and Prions Chapter 21 Viruses, Bacteria & Archaea Reproduction of Viruses: 1. Attachment: Virus gains entry into specific host cell based on host-specific match between virus surface molecules and host cell receptors. 2. Penetration: Host cell engulfs virus or virus injects its genome into the cytoplasm. 3. Biosynthesis: New viral components are synthesized using host cell’s machinery and energy. 4. Maturation: 5. Release: New viruses exit host cell through lysis or budding in order to infect new host cells.

Viruses, Viroids, and Prions Biology, 9th ed,Sylvia Mader Viruses, Viroids, and Prions Chapter 21 Viruses, Bacteria & Archaea Bacteriophages – Viruses that infect bacterial cells There are two types of bacteriophage life cycles. The lytic cycle Viral reproduction occurs Hundreds of virus particles are released The lysogenic cycle Viral reproduction does not occur immediately but may occur in the future. Virus becomes integrated into the host genome and may reenter lytic cycle. Diphtheria is caused by a prophage-carrying bacterium, which produces a toxin that damages the lining of the upper respiratory tract, restricting breathing.

Viruses, Viroids, and Prions Biology, 9th ed,Sylvia Mader Chapter 21 Viruses, Viroids, and Prions Viruses, Bacteria & Archaea Reproduction of Animal Viruses: Animal virus enters the host cell Uncoating releases viral DNA or RNA Budding: Acquires a membranous envelope Retroviruses (HIV, the virus that causes AIDS) Contain reverse transcriptase Carries out RNA  cDNA reverse transcription cDNA becomes integrated into host DNA HIV may remain latent for years Viral DNA is transcribed; new viruses are produced

Biology, 9th ed,Sylvia Mader Flu Virus Chapter 21 Viruses, Bacteria & Archaea A flu virus has an H (hemagglutinin) spike and an N (neuraminidase) spike H spike allows the virus to bind to the receptor 16 different types N spike attacks host plasma membranes Allows mature viruses to exit the cell 9 different types Our immune system only recognizes H spikes and N spikes it has been exposed to. Currently the H7N9 and H5N1 subtypes of flu virus are of great concern because they can potentially become pandemics (global outbreaks).

Biology, 9th ed,Sylvia Mader Chapter 21 Emerging Viruses Viruses, Bacteria & Archaea Emerging viruses are new or previously uncommon illnesses. Examples are AIDS, West Nile encephalitis, hantavirus pulmonary syndrome (HPS), severe acute respiratory syndrome (SARS), Ebola, hemorrhagic fever, and avian influenza Several types of events can cause emergence of viruses A virus may extend its range. A genetic mutation may occur. Example: Influenza strains H5N1, H1N1, and H7N9 were created through mutation of flu viruses which only infected animals It is necessary to obtain flu vaccine each year due to the rapidly mutating flu virus

Viruses, Viroids, and Prions Biology, 9th ed,Sylvia Mader Viruses, Viroids, and Prions Chapter 21 Viruses, Bacteria & Archaea Viruses are best known for causing infectious diseases in plants and animals. Herpes, HIV, cancer Viruses lack metabolism; thus, antibiotics have no effect Viroids Naked strands of RNA Prions Protein molecules with contagious tertiary structure TSEs are neurodegenerative diseases which destroy nerve tissue in the brain They are untreatable and fatal Some practices, including eating brains of cattle, transmitted the cattle disease (BSE or bovine spongiform encephalopathy) to humans.