Viruses, Bacteria & Archaea Chapter 21

Viruses, Bacteria & Archaea 2OutlineViruses  Structure  Classification  Reproduction Prokaryotes  Structure  Reproduction  Nutrition BacteriaArchaea

Viruses, Bacteria & Archaea 3 The Viruses Viruses are noncellular and thus cannot be classified with cellular organisms Generally smaller than 200 nm in diameter Each type has at least two parts  Capsid: Outer layer composed of protein subunits ­Some enveloped by membrane ­Others “naked”  Nucleic acid core: DNA or RNA Vary in shape from thread-like to polyhedral

4 Viruses

Viruses, Bacteria & Archaea 5 Parasitic Nature Viruses are:  Obligate intracellular parasites  Cannot reproduce outside a living cell  Can be cultured only inside living cells ­Chicken egg ­Tissue culture

Viruses, Bacteria & Archaea 6 The Bacteriophages: Reproduction Bacteriophages – Viruses that infect bacterial cells Portions of capsid adhere to specific receptor on the host cell Viral nucleic acid enters the cell Once inside, the virus takes over metabolic machinery of the host cell

Viruses, Bacteria & Archaea 7 Bacteriophages: The Lytic Cycle Lytic cycle may be divided into five stages:  Attachment  Penetration  Biosynthesis  Maturation  Release

Viruses, Bacteria & Archaea 8 The Bacteriophages: The Lysogenic Cycle Phage becomes a prophage  Becomes integrated into the host genome  Becomes latent  May later reenter the lytic cycle

9 Lytic and Lysogenic Cycles in Prokaryotes

Viruses, Bacteria & Archaea 10 Reproduction of Animal Viruses Animal virus enters the host cell Uncoating releases viral DNA or RNA  Budding: ­Viral particles released in a bud ­Acquires a membranous envelope  Retroviruses (AIDS) ­Contain reverse transcriptase ­Carries out RNA  cDNA reverse transcription ­cDNA becomes integrated into host DNA

11 Reproduction of the Retrovirus HIV-1

Viruses, Bacteria & Archaea 12 Viral Infections 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 ­Many crop diseases  Prions ­Protein molecules with contagious tertiary structure ­Some human and other animal diseases - Mad cow disease

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Emerging Diseases 14

Viruses, Bacteria & Archaea 15 The Prokaryotes Include bacteria and archaea, which are fully functioning cells  A single spoonful of earth can contain >1000 prokaryotes  Range in size from 1-10 µm in length and µm in width

16 Pasteur’s Experiment

Viruses, Bacteria & Archaea 17 Prokaryote Structure Lack a membrane-bounded nucleus (DNA in nucleoid region) Outer cell wall containing peptidoglycan Some move by means of flagella Lack membranous organelles May have accessory ring of DNA (plasmid)

Viruses, Bacteria & Archaea 18 Reproduction in Prokaryotes Asexual  Prokaryotes reproduce asexually by means of binary fission Methods of genetic recombination  Conjugation ­Sex pilus forms between two cells ­Donor cell passes DNA to recipient cell through pilus  Transformation  Transduction

Viruses, Bacteria & Archaea 19 Reproduction in Prokaryotes Transformation  Occurs when bacterium picks up free pieces of DNA from other prokaryotes  Becomes incorporated into genome Transduction  Occurs when bacteriophages carry portions of bacterial DNA from one cell to another  Serve as vectors Some bacteria form resistant endospores under unfavorable conditions

Viruses, Bacteria & Archaea 20 Prokaryotic Nutrition Oxygen requirements:  Obligate aerobes – unable to grow in the absence of free oxygen  Obligate anaerobes – unable to grow in the presence of free oxygen  Facultative anaerobes – able to grow in either the presence or absence of free oxygen

Viruses, Bacteria & Archaea 21 Autotrophic Prokaryotes Photoautotrophs  Use solar energy to reduce carbon dioxide to organic compounds  Photosynthetic Chemoautotrophs  Oxidize inorganic compounds to obtain the necessary energy  Use it to reduce CO 2 to an organic compound  Chemosynthetic

Viruses, Bacteria & Archaea 22 Heterotrophic Prokaryotes Most prokaryotes are chemoheterotrophs that take in organic nutrients  Aerobic saprotrophs decompose most large organic molecules to smaller molecules  Essential components of healthy ecosystem May be free-living or symbiotic  Nitrogen fixation  Commensalism  Parasites

Viruses, Bacteria & Archaea 23 The Bacteria Bacteria are commonly diagnosed using the Gram stain procedure When washed after staining:  Gram-positive bacteria retain dye and appear purple  Gram-negative bacteria do not retain dye and appear pink

24 Diversity of Bacteria

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Viruses, Bacteria & Archaea 26Cyanobacteria Formerly called the Blue-Green algae (Cyanophyta) Cyanobacteria are Gram-negative bacteria that photosynthesize Believed to be responsible for introducing oxygen into the primitive atmosphere  Lack visible means of locomotion  Can live in extreme environments  When commensals with fungi, form lichens

27 Diversity Among the Cyanobacteria

Viruses, Bacteria & Archaea 28 The Archaea Archaea were earlier considered bacteria Carl Woese discovered that the base sequence of their rRNA differs from Bacteria Other differences:  Archaea do not have peptidoglycan in their cell walls like the Bacteria  Archaea biochemical more like Eukarya than Bacteria Archaea now thought to be more closely related to Eukarya than to Bacteria

Viruses, Bacteria & Archaea 29 Archaea Metabolism Most are chemoautotrophs Some mutualistic Some commensalistic None known to be parasitic None are photosynthetic Many live in harsh conditions

Viruses, Bacteria & Archaea 30 Types of Archaea Many live in harsh conditions:  Anaerobic marshes ­Methanogens ­Produce methane from hydrogen gas and carbon dioxide  Salty lakes ­Halophiles ­Require high salt concentrations for growth, and  Hot sulfur springs ­Thermoacidophiles ­Reduce sulfides and survive best at temperatures above 80ºC ­Plasma membranes contain unusual lipids convey tolerance of high temperatures

31 Thermoacidophile Habitat and Structure

Viruses, Bacteria & Archaea Ending Slide Chapter 21