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 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