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Eukaryotes • • • • • • fossil eukaryotes 2 bya “true nucleus” (prokaryote = “before nucleus”) linear chromosomes membrane bound compartments Figs 6.9, 6.6 Eukaryotes • distinctive flagella: • 9 + 2 microtubules • inserted into cytoplasm • surrounded by membrane • Fig 6.24 Independent origin of flagella • • • • Prokaryotes globular protein flagellin attached to outer membrane Fig 27.6 • note: singular of flagella is flagellum • similar to bacteria & bacterium Origin of Eukaryotic Cell Fig 25.9 Serial Endosymbiosis Theory • explains how eukaryotic cell evolved • prokaryotic symbionts evolved into mitochondria & chloroplasts • symbiont lives INSIDE host cell (intracellular symbiont) • starts as prey (not digested) or parasite (not lethal) Serial Endosymbiosis Theory • • • • • symbiont genes move to host nucleus proteins transported to symbiont symbiont & host become dependent new organism has evolved well accepted; lots of evidence: 1. Similarities between bacteria & mitochondria and plastids • • • • • Size Circular DNA w/out assoc. proteins Binary fission Ribosome size, biochemistry RNA sequence data 2. Eukaryotic cell biology • DNA from organelle in host nucleus • Some DNA still in organelle • Euk. cells deprived of mito & chlplst CANNOT reproduce them 3. Evidence of Past Symbiosis • Glaucophytes • Chlplst CANNOT live indply • Chlplst has small peptidoglycan wall 4. Modern Day Symbiosis • Paramecium bursaria • Host and symbiont CAN live indply • Remove symbionts, host re-acquires Types of Endosymbiosis Fig 28.2 • • • • • • Primary: symbiont is prok. 2 chlplst membranes Secondary: symbiont is euk. Evidence for 2ndary endosymbiosis: Extra chlplst membranes Remains of nucleus = nucleomorph (in two lineages) protist = “the very first” • Modern relatives of earliest euk. • “protists” = eukaryotes that are NOT plants, animals, or fungi • 60,000 species known • diverse lineages not closely related • heterotrophs, autotrophs in same lineage (also mixotrophs) • all w/ PS have chlorophyll a; accessory pigments vary between lineages body forms of “protists” • unicells, colonies, multicellular relatives • diversity of form within lineages • unicellular—>multicellular many times • complex unicells: all functions one cell • larger multicellular protists provide habitat ecological roles of “protists” • unicellular (chemo)heterotrophs = protozoa – Protozoology • (photo)autotrophs = algae – Phycology or Algology (includes photosynthetic protists & cyanobacteria) – primary producers, base of food web • small protists are plankton – zooplankton & phytoplankton • Fig 28.28 role of plankton in C cycle • • • • • PS: H2O + CO2 --> (CH2O) + O2 die & fall as “marine snow” C sinks resistant compounds degrade slowly CO2 removed from atmosphere phytoplankton decline • water transparency – secchi disk – since 1899 – >100 yrs of data • chlorophyll conc. • temp increase Nature July 29, 2010
