Outline. Viruses, Bacteria, and Archaea. Viruses Structure Classification Reproduction Prokaryotes Structure Reproduction Nutrition Bacteria Archaea

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1 Viruses, Bacteria, and Archaea Chapter 21 Viruses Structure Classification Reproduction Prokaryotes Structure Reproduction Nutrition Bacteria Archaea Outline The Viruses 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.! Nucleic acid core: DNA or RNA.

2 Fig. 21.1ba Fig. 21.1bb The Viruses The Viruses Classification is based on: Type of nucleic acid. Size and shape. Presence / absence of outer envelope.

3 Fig. 21.1c Fig. 21.1d Fig. 21.1p363ba Parasitic Nature Viruses are obligate inrtracellular parasites (cannot reproduce outside a living cell). Can infect a wide variety of cells, but are very specific.! Bacteriophages - Infect bacterial cells.

4 Viral Reproduction Viruses gain entry into host because portions of capsid adhere to a specific receptor on the host cell s outer surface. Viral nucleic acid enters the cell and once inside, the nucleic acid codes for the protein units inside the capsid.! Virus takes over metabolic machinery of the host cell. Lytic Cycle Lytic cycle may be divided into five stages: Attachment Penetration Biosynthesis Maturation Release Fig Virus Lytic Cycle 15

5 Fig. 21.3a Lysogenic Cycle Phage becomes a prophage that is integrated into the host genome. Becomes latent, and later may reenter the lytic cycle. Reproduction of Animal Viruses Reproduction of HIV-1 After animal viruses enter the host cell, uncoating releases viral DNA or RNA and reproduction occurs. If viral release occurs by budding, the viral particle acquires a membranous envelope. Retroviruses! Contain reverse transcriptase which carries out RNA " cdna transcription.

6 Viral Infections TA p362 Viruses are best known for causing infectious diseases in plants and animals. Herpes, HIV, cancer! Viruses lack enzymes; thus, antibiotics have no effect. Many crop diseases have been attributed to viroids (naked strands of RNA). Some human and other animal diseases have been attributed to prions (protein molecules).! Mad cow disease The Prokaryotes TA p368 The prokaryotes include bacteria and archaea, which are fully functioning cells. A single spoonful of earth can contain prokaryotes. Range in size from 1-10!m in length and !m in width.

7 Fig Prokaryote Structure Lack a eukaryotic nucleus. Have outer cell wall containing peptidoglycan. Some move by means of flagella. Lack membranous organelles. Contain nucleoid. May have accessory ring of DNA (plasmid). Flagella Bacterial Diversity 28

8 Reproduction in Prokaryotes Binary Fission Prokaryotes reproduce asexually by means of binary fission. Conjugation occurs between bacteria when the donor cell passes DNA to recipient cell by way of sex pilus. TA p369 Reproduction in Prokaryotes Transformation occurs when bacterium picks up free pieces of DNA from other prokaryotes. Transduction occurs when bacteriophages carry portions of bacterial DNA from one cell to another. When faced with unfavorable conditions, some bacteria form endospores.

9 Fig Prokaryotic Nutrition Obligate anaerobes are unable to grow in the presence of free oxygen. Facultative anaerobes are able to grow in either the presence or absence of gaseous oxygen. Autotrophic Prokaryotes Photoautotrophs use solar energy to reduce carbon dioxide to organic compounds. Photosynthetic Chemoautotrophs oxidize inorganic compounds to obtain the necessary energy to reduce CO 2 to an organic compound. Chemosynthetic Heterotrophic Prokaryotes Most prokaryotes are chemotrophs that take in organic nutrients. Aerobic saprotrophs decompose most large organic molecules to smaller molecules. May be free-living or symbiotic. Nitrogen fixation Commensalism

10 The Bacteria Groups of bacteria are commonly differentiated from one another using the Gram stain procedure. Gram-positive bacteria retain dye and appear purple. Gram-negative bacteria do not retain dye and appear pink. The Bacteria Bacteria can also be classified in terms of their three basic shapes. Spiral (spirilli), Rod (bacilli), and Round (cocci). Cyanobacteria Cyanobacteria 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.! In association with fungi, form lichens.

11 Fig c The Archaea Archaea were considered bacteria until Carl Woese discovered their rrna has a different sequence of bases than rrna of bacteria. Eukarya are believed to be more closely related to archaea than to bacteria. Archaea Structure and Function Plasma membranes of archaea contain unusual lipids that allow them to function at high temperatures. Some are methanogenic. Most are chemoautotrophs. None are photosynthetic. Sometimes mutualistic or commensalistic, but none are parasitic. Methanogens Types of Archaea Found in anaerobic environments.! Produce methane from hydrogen gas and carbon dioxide. Halophiles Require high salt concentrations for growth. Thermoacidophiles Reduce sulfides and survive best at temperatures above 80 o C.

12 Viruses Structure Classification Reproduction Prokaryotes Structure Reproduction Nutrition Bacteria Archaea Review