Transcript Prokaryote Cell Structures

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
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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
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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