The Cell: Basic Unit of Life Prokaryotes and the Evolution of Eukaryotes

Universe is billion years old Atmosphere H first then other gases Earth solidifies 4.1 bya 1st photosynthetic prokaryotes 3.5 bya Figure 16.1C = 500 million years ago Earliest animals; diverse algae Earliest multicellular eukaryotes? Earliest eukaryotes Accumulation of atmospheric O 2 from photosynthetic cyanobacteria Oldest known prokaryotic fossils Origin of life? Formation of Earth Billions of years ago Early earth and the origin of life

Universal Cell Components cell membrane cytoplasm genetic material (DNA) ribosomes –for protein synthesis Campbell Fig. 7.4

Figure 16.2a-0 Cocci Bacilli Spirochete Bacteria The Smallest, Simplest Cells ALL BACTERIA ARE PROKARYOTES  m

Prokaryotic Features DNA is in a single-stranded loop –No chromosomes, mitosis, or meiosis –Lack a membrane-bound nucleus No mitochondria, chloroplasts, or other organelles Cell walls are chemically unlike any eukaryote cell walls

Bacterial Cell Features Campbell Fig. 7.4

Advanced Prokaryote Features Campbell Fig Campbell Fig compare Campbell Fig interior membranes bacterial flagellum some are photo-autotrophic

Bacteria are Important Pathogens (“disease-causing”) are parasites on living cells and organisms Decomposers rot dead material, recycling essential nutrients Mutualists with - –plants: root-knot rhizobia fix nitrogen –fungi: cyanobacteria are part of lichens –animals: intestinal bacteria digest cellulose

Commercial Bacteria Lactose-users make yogurt and cheese Soil bacteria make many antibiotics Intestinal bacteria used as “lab rats” in cell biology Cyanobacteria are important for marine and freshwater food chains

3 Domains of Life Archaea are also prokaryotes Recently separated from Bacteria –Cell wall chemistries are different –Archaea genes more like eukaryotes’ Only Eukarya have a proper nucleus

Phylogeny of Domains BacteriaArchaeaEukarya prokaryotes

Archaea unusual environmental tolerances: –extreme halophiles –extreme thermophiles –methanogens Campbell Fig

true cell nucleus: –nuclear membrane –linear DNA, organized into chromosomes –replicate by mitosis and meiosis Plants, animals, and fungi are eukaryotes. Many unicellular algae and protozoans are also eukaryotes. Eukaryotes

Evolution of Eukaryotic Cells Campbell Fig Step 1: Nuclear and endo- plasmic membranes (kingdom Archezoa) Step 2: Organelles acquired by symbiosis (remaining 7 kingdoms)

Organelles Bacteria that were parasites, became mutualists –mitochondria burn sugars, etc., for energy –chloroplasts photosynthesize more energy –chloroplasts were lost during evolution of many living eukaryotes, such as animals and fungi

Mitochondrion Campbell Fig Chloroplast Campbell Fig External and internal membranes (compare to early stages of eukaryote cell evolution)

Cytoplasmic Movements microfilaments in cell Campbell Fig. 7.27

Eukaryote Locomotion All is based on contractile fibers mitotic spindle and centrioles eukaryote flagellum and cilia ameboid movement and cytoplasmic streaming double fibrils

Campbell Fig FlagellumCilia

Early earth and the origin of life Universe is billion years old Atmosphere H first then other gases Earth solidifies 4.1 bya 1st photosynthetic prokaryotes 3.5 bya