prokaryotes and viruses. characteristics of prokaryotic cells single-celled bacteria and archaeans ...
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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 Structures
Typical surface structures• Cell wall• Outermost protective capsule or slime layer• One or more flagella• Pili
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)
Archaean Physiology
Halophiles (salt lovers), extreme thermophiles, and methanogens (methane makers)
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
Prion InfectionsPrions
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
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
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
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
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)
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
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