BIOL 112 1st Edition Lecture 11 Outline of Last Lecture I Problems with Earliest Divergences II LUCA III The Prokaryotic Cell IV Cell Wall Biochemistry V Gram Positive Gram Negative VI Ways to Organize the Cell Wall VII Structures Outside Cell Membrane VIII Structures Inside Cell Membrane IX Metabolism Nutrition X Autotrophy Outline of Current Lecture XI Heterotrophy XII Systematics Taxonomy XIII Three Domains XIV Domain Archaea XV Domain Bacteria XVI Recent Historical Trends XVII Distinguishing Characteristics of Eukarya XVIII Endosymbiont Theory XIX Sequence of Endosymbiotic Events These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Current Lecture I Heterotrophy Obtains energy and carbon structures from consumption of organic matter Must eat something organic Photoheterotrophs Can photosynthesize but still need organic carbon source for syntheses Chemoheterotrophs Most prokaryotes fit into this category Differ ent types depending upon source of carbon food Saprobes Decayers decomposers Absorb nutrients from enzymatic hydrolysis of dead organic matter Critical components in ecological systems recycle specific ele ments N P C S within system Symbionts Some prokaryotes live in association with other organ isms derive carbon nutrients from living organic matter host Mutualism relationship is beneficial to both partners Commensalism one symbiont benefits while the host is neither harmed nor helped Parasitism Symbiont benefits host is harmed Prokaryotic para sites are also known as pathogens disease causers II Systematics Taxonomy Prokaryotic and lower eukaryotic systematics are undergoing major revisions Consequence of lots and new molecular data that is being collected Data and new relationships are still being sorted out so present schemes will undoubtedly be revised more in coming years One consequence is development of domains reflecting fundamental ancient evolutionary divergences There are three domains III Three Domains Domain Archaea Archaebac teria Probably represent extremely ancient forms similar to life on the planet 2 3 billion years ago More similarities to eukaryotes than to bacteria Prokaryotic adapted to living in extremely harsh environments not available to other life forms but recent work indicates they might be widely distributed in common environments as well Domain Bacteria True bac teria Prokaryotic cells most classical bacterial forms Domain Eukarya Eukaryotes IV Domain Archaea Very ancient like forms have a number of fundamental differences from true bacteria which distinguish them Cell Walls variable content Many use proteins in cell wall No peptidoglycan Cell Membrane Lipid content differs some lipid moieties are branched Ribosomes and RNA polymerase more like eukaryotic forms than other prokaryotes drug sensitivity also eukaryote like Archaea are more common than originally thought Originally thought to be limited to extreme environments on Earth Extreme hot acid or anaerobic or saline conditions But now apparently more common DNA sequences identified from wide range of environments on Earth including symbiotic forms Microscopic surveys show many organisms not otherwise iden tified Culture conditions for archaeans are not understood and not eas ily defined so ability to grow them in the lab and characterize them is very limited Four Kingdoms K Euryarchaeota K Crenarchaeota K Korarchaeota K Nanoarcheota Great proliferation of knowl edge about Archaeans in the past 25 years Originally thought to be rare and found only in unusual extreme environments V Domain Bacteria True bacteria Prokaryotic but with many features that distinguish them from archaeans see comparison chart on previous page Extremely diverse group in terms of physiology biochemistry nutri tion ecology Some species are autotrophic some heterotrophic Some free living some symbiotic Etc VI Recent Historical Trends Abandonment of K Protista as a valid taxon Continued elevation of lower taxa to higher levels of Linnaean hier archy Phylum Protozoa Kingdom Protista Several Kingdoms of Protists Proliferation of taxa More and more groups with fewer species in each Movement away from morphological criteria to define taxa towards molecular biochemical dynamic criteria VII Distinguishing Characteristics of Eukarya Eukaryotic Cell Organization Single celled or colonial No more than 1 tissue type in cell mass Most species are single celled and microscopic bigger than most prokaryotes Diverse lifestyles nutrition motility At least 120 000 species VIII Endosymbiont Theory Certain major organelle types in modern eukaryotic cell have separate ancestral lineages distinct from that of other cell parts These organelles were once independent organisms but now are in a tight mutualistic symbiotic relationship comprising modern eukaryote Thus eukaryotic cell is a collection of original cell types living in rela tion to one another Evidence for Endosymbiosis Chloroplasts and mitochondria have their own distinct inheritance patterns and their own genetics Morphology and size similar to bacteria similar to gram negative forms New chloroplasts and mitochondria arise only from the division replication of existing organelles Complete removal of mitochondria or chloroplasts from cells with these organelles results in their permanent loss Host cell has no way to regenerate lost organelles Both chloroplasts and mitochondria contain their own DNA have their own full set of genetic expression enzymes and cofactors and posses ribosomes more like bacterial ribosomes DNA in these organelles is circular in most species IX Sequence of Endosymbiotic Events Ancestral eukaryotic cell could do glycolysis only anaerobic No photosynthesis or oxidative phosphorylation First event elaboration of membranes to form endomembrane system nuclear envelope endooplasmic reticulum golgi At some point urkaryote internalized an aerobic prokaryote Over time genes are transferred from symbiont to host genome lateral gene transfer so that mitochondrial genome now is of minimal size Most genes needed for mitochondrion protein array come from nuclear expression Organelles surrounded by double membranes inner membranes are unique Inner mitochondrial and chloroplast membranes are unlike other membranes in eukaryotic cell in terms of protein lipid ratio structural organization and enzyme content and are more like the membranes of bacteria than those of