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Prokaryotes and Viruses Characteristics of Prokaryotic Cells Single-celled bacteria and archaeans No nucleus or membrane-bound organelles Smallest, most widely distributed, numerous, and metabolically diverse organisms • Autotrophs and heterotrophs Prokaryote Cell Shapes Spheres (cocci), rods (bacilli), spirals (spirilla) Prokaryote Cell Structures Typical surface structures • • • • Cell wall Outermost protective capsule or slime layer One or more flagella Pili A Prokaryotic Cell Flagella and Pili Prokaryotic Fission Prokaryotic Cell Characteristics The Bacteria The most common and diverse prokaryotes • Some are pathogens (cause disease in a host) Food Poisoning Bacterial Diversity: Cyanobacteria Oxygen-releasing photoautotrophs • Chloroplasts probably evolved from ancient cyanobacteria by endosymbiosis Bacterial Diversity: Gram-Positive Bacteria Have thick walls • Endospores resist heat, boiling, irradiation, acids and disinfectants • Some are human pathogens Bacterial Diversity: Chlamydias Chlamydias • All are intracellular parasites of animals • Obtain ATP from host cells • Some sexually transmitted diseases (C. trachomatis) Bacterial Diversity: Spirochetes Spring-shaped • Live on their own or in hosts • Some are pathogens Archaean Physiology Halophiles (salt lovers), extreme thermophiles, and methanogens (methane makers) Archaeans in Extreme Environments The Viruses Viruses are noncellular infectious particles that cannot reproduce on their own Viruses infect a host cell; their genes and enzymes take over the host’s mechanisms of replication and protein synthesis Viral Structures Prion Infections Prions Proteins that occur naturally in the vertebrate nervous system, but can cause fatal disease when they misfold Antibiotic Resistance Use of antibiotics favors antibiotic-resistant bacteria Genes that convey drug resistance can arise by mutation, may spread among members of the same or different species by conjugation Protists – The Simplest Eukaryotes An Evolutionary Road Map Protists • The simplest eukaryotes • Most are single-celled • Some are multicelled and large Protist Structure Protist cells have a nucleus (eukaryotes) Most have one or more mitochondria Many have chloroplasts that evolved from cyanobacteria or from another protist Dominant stage of life cycle: Haploid or diploid Protist Evolutionary Tree Comparing Prokaryotes and Eukaryotes Key Concepts: SORTING OUT THE PROTISTS Protists include many lineages of single-celled eukaryotic organisms and their closest multicelled relatives Gene sequencing and other methods are clarifying how protist lineages are related to one another and to plants, fungi, and animals Ancient Flagellates Flagellated protozoans • Single-celled heterotrophs with flagella • Unwalled cells, pellicle retains shape Most euglenoids live in freshwater • Some have chloroplasts that arose by secondary endosymbiosis from a green alga • Contractile vacuoles expel excess water Disease-Causing Flagellates Trichomonas vaginalis Trypanosoma brucei Shelled Amoebas Foraminiferans and radiolarians • Single-celled heterotrophs with a secreted shell • Many openings for pseudopods Alveolates All alveolates have tiny sacs (alveoli) beneath the plasma membrane • All single-celled Examples: • Ciliates, dinoflagellates, and apicomplexans Ciliates Aquatic predators and parasites with many cilia • Example: Paramecium Dinoflagellates Aquatic heterotrophs and autotrophs with a cellulose covering • Photosynthetic protists cause algal blooms in nutrient-rich water Apicomplexans Heterotrophs: Parasites living in animal cells • • • • Cell-piercing structure made of microtubules Reproduce sexually and asexually in host cells Only gametes have flagella Example: Plasmodium (malaria) Malaria Plasmodium species cause malaria Single-Celled Stramenopiles Two flagella, one with hairlike filaments Oomycotes • Heterotrophs (decomposers and parasites) that grow as a mesh of absorptive filaments • Some parasitic species are important plant pathogens Photosynthetic Stramenopiles Diatoms, coccolithophores, and golden algae • Often part of the phytoplankton • Photosynthetic cells (contain fucoxanthin) Hard parts accumulate as mineral deposits • Coccolithophores (calcium carbonate plates): Chalk and limestone • Diatoms (silica shells): Diatomaceous earth Stramenopiles of the Phytoplankton Brown Algae Multicelled, photosynthetic stramenopiles • Include microscopic strands and giant kelps (the largest protists; ecological and commercial value) Green Algae Chlorophytes (most green algae) and charophytes (closest relatives of plants) • Have chloroplasts with chlorophylls a and b • Store carbohydrates as starch grains Red Algae Most red algae are multicelled • Cultivated for commercial products Amoebozoans Amoebas (single cells) and slime molds (“social amoebas”) • Heterotrophic, free-living Slime Molds Plasmodial slime molds • Feed as a multinucleated mass