Prokaryotes and Viruses. Characteristics of Prokaryotic Cells Single-celled bacteria and archaeans No nucleus or membrane-bound organelles Smallest,

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 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

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