Chapter 21 Viruses Bacteria Archaea 2 Outline Viruses

Chapter 21 Viruses, Bacteria & Archaea

2 Outline Viruses Structure Classification Reproduction Prokaryotes Structure Reproduction Nutrition Bacteria Archaea

3 The 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

Viruses 4

5 Viral Categorization Classification is based on: Type of nucleic acid Size and shape Presence / absence of outer envelope

6 Parasitic Nature Viruses are: Obligate intracellular parasites Cannot reproduce outside a living cell Can be cultured only inside living cells Chicken egg Tissue culture

“Growing” Viruses 7

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 8

Bacteriophages: The Lytic Cycle Lytic cycle may be divided into five stages: Attachment Penetration Biosynthesis Maturation Release 9

The Bacteriophages: The Lysogenic Cycle Phage becomes a prophage Becomes integrated into the host genome Becomes latent May later reenter the lytic cycle 10

Lytic and Lysogenic Cycles in Prokaryotes 11

12 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 c. DNA reverse transcription c. DNA becomes integrated into host DNA

Reproduction of the Retrovirus HIV-1 13

14 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

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 0. 7 -1. 5 µm in width

Pasteur’s Experiment 16

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)

Flagella 18

19 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

Fimbriae and Sex Pilus 20

Binary Fission 21

22 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

The Endospore of Clostridium tetani 23

24 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

25 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

26 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

Nodules of a Legume 27

28 The 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

29 The Bacteria Structure of cell wall also of diagnostic use Bacteria can be further classified in terms of their three basic shapes Spiral (spirilli), Rod (bacilli), and Round (cocci)

Diversity of Bacteria 30

31 Cyanobacteria 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

Diversity Among the Cyanobacteria 32

33 The Archaea were earlier considered bacteria Carl Woese discovered that the base sequence of their r. RNA 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

34 Archaea Metabolism Most are chemoautotrophs Some mutualistic Some commensalistic None known to be parasitic None are photosynthetic Many live in harsh conditions

35 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