Life 103 2nd week
Life 103 2nd week LIFE 103
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This 5 page Class Notes was uploaded by Caroline Hurlbut on Friday January 29, 2016. The Class Notes belongs to LIFE 103 at Colorado State University taught by Jennifer L Neuwald; Tanya Anne Dewey in Fall 2016. Since its upload, it has received 18 views. For similar materials see Biology of Organisms-Animals and Plants in Biology at Colorado State University.
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Date Created: 01/29/16
Bacteria & Archaea • Laguna Salada de Torrevieja in Spain can reach a salt concentration of ~32% and appears pink —color due to prokaryotic halobacteria with red membranes that photosynthesize in the salty water • domains bacteria and archaea are entirely prokaryotes and can thrive in extreme environments —most abundant organisms —can live in pH <1 or >12 and at temps >100˚C —earth’s ﬁrst organisms likely prokaryotes —eukarya and archaea most closely related domains • we know so little about prokaryotes because they are so small —99% of bacteria and archaea are not culturable —we learn about uncultured diversity by studying DNA from different environments • common shapes of prokaryotic cells —cocci (spheres) —bacilli (rods) —spirals • components in all bacterial cells —nucleoid —cytoplasm —plasma membrane —cell wall • some bacterial cells have —capsules: polysaccharide or protein layer that provides protection and a means of attachment —ﬂagella —sex pili: for horizontal gene transfer • prokaryotic DNA —much less DNA than eukaryotes —most of genome consists of circular chromosome located in nucleoid —some species have smaller rings of DNA called plasmids • cell surface structure —cell wall maintains shape, protects cell, and protects it from bursting in hypotonic environments —while eukaryotic cell walls are made of cellulose or chitin, bacterial cell walls contain peptidoglycan, a rigid network of sugars and polypeptides —target of many antibiotics (ex. penicillin) is to disrupt cell wall—>lysis (rupture of cell) • bacterial endospores —dormant bodies of genetic material used by vegetative cells of Bacillus and Clostridium to continue life in case of harsh conditions, most resistant of all life forms —depletion of nutrients triggers calcium covering of endospores • motility —taxis: ability to move toward or away from a stimulus using embedded tails called ﬂagella • factors of prokaryotic reproduction —asexual reproduction by binary ﬁssion —very small —short generation times • diverse nutritional and metabolic adaptations have evolved in prokaryotes • prokaryotes can be categorized by how the obtain energy and carbon —phototrophs: obtain energy from light —chemotrophs: obtain energy from chemicals —autotrophs: “self-feeders” that require CO2 as carbon source —heterotrophs: require organic nutrients to make organic compounds • prokaryotic metabolism varies with respect to O2 —obligate aerobes: require O2 for cellular respiration —obligate anaerobes: use fermentation or anaerobic respiration —facultative anaerobes: can survive with or without O2 (ex. muscle cells) • what traits allow such diversity and high adaptiveness? —small size —rapid generation time —endospores: durable resting stage and easily dispersible —genetic recombination • genetic recombination - combining of DNA from two sources • prokaryotic DNA from different individuals can be brought together by —transformation: gathering of naked DNA fragments —transduction: transfer of DNA by bacteriophage —conjugation: transfer of DNA between bacteria through the sex pilus (piece of DNA called the F factor required to produce pili), also called horizontal gene transfer • causes of horizontal gene transfer —exchange of transposable elements and plastids —viral infection —fusion of organisms • differences between prokaryotes and eukaryotes • archaea are extremophiles —halophiles (saline environments) —thermophiles (hot environments) —methanogens (anoxic environments, produce methane as waste) • pathogens - disease causing organisms —positive and negative interactions with humans —bacteria cause about half of all human diseases —some bacterial diseases are transmitted by other species —Yersinia pestis—>bubonic plague spread by ﬂeas through rodents Phylogeny & the Tree of Life geologic record - standard time scale for presence of life on earth over the last 3.5 • billion years • types of classiﬁcation —Linnaeus: binomial classiﬁcation —phylogenies: use of molecular and morphological traits to infer evolutionary relationships —domains: reorganization of kingdoms using endosymbiotic theory • Linnaeus classiﬁcation —created “bins” of similar organisms—>taxonomy —hierarchal system: kingdom, phylum, class, order, family, genus, species —binomial nomenclature is the scientiﬁc two-name system for naming organisms (Genus, species) • accurate taxonomy should reﬂect evolutionary relatedness and individuals within a bin should contain all the organisms that share a common ancestor • phylogeny - evolutionary history of a group of organisms, represented by branching diagram called phylogenic tree • systematics classiﬁes organisms and determines evolutionary relationships • nodes on a phylogenic tree point to a common ancestor between organisms • homology - phenotypic and genetic similarities due to shared ancestry • analogy - similarity due to convergent evolution • convergent evolution occurs when similar environmental pressures and natural selection produce similar adaptations in organisms from different evolutionary lineages • an organism’s evolutionary history is documented in its genome —DNA that codes for rRNA changing slowly over time is an example of a conserved gene, which is used to explore ancient evolutionary events —mitochondrial DNA evolving rapidly is an example of what is used t explore recent evolutionary events • 3-domain system adopted —bacteria (prokarytes) —archaea (prokaryotes) —eukarya (eukaryotes) • endosymbiotic theory —Lynn Margulis proposed that mitochondria/chloroplasts in eukaryotes came from symbiotic bacteria —probably led to development of heterotrophic and autotrophic organisms • advent of mitochondria led to explosion in diversity —aerobic respiration gives considerable energy advantage • horizontal gene transfer - movement of genes between genomes, has played a key role in evolution of prokaryotes and eukaryotes • 3D “web” of life is a more accurate description of the history of life, with a tangled network of connected branches instead of an organized tree Protists & Algae • protist - historic term unrelated to evolutionary history; anything that isn’t a plant, animal, fungus, or prokaryote; “junk drawer” of taxonomy • DNA sequencing has eliminated the kingdom Protista • most protists are unicellular • 4 supergroups within Eukarya —Excavata —“SAR” clade —Archaeplastida —Unikonta • protists arose due to endosymbiosis, when an ancestral bacterium engulfs another and they develop a mutually beneﬁcial relationship —proteobacteria—>mitochondria —cyanobacteria—>chloroplasts • Excavata - “excavated” groove on body; 3 monophyletic groups —diplomonads: lack plastids and have unique mitochondria (mitosomes) —parabasalids: lack plastids and have unique mitochondria (mitosomes) —euglenozoans • SAR clade - deﬁned by DNA similarities; recently organized by whole genome data; 3 major clades —*stramenophiles: hairy ﬂagella (ex. diatoms, gold/brown algae), some of the most important photosynthetic organisms on earth —*alveolates: membrane sacs (ex. plasmodium - cause of malaria) —*rhizarians: pseudopodia and cilia (ex. amoebas) • Archaeplastida - parent group of modern land plants, all descended from co-opted cyanobacteria —red/green algae: closest relatives of land plants —2 subgroups of green algae A. *charophytes - most closely related to land plants B. chlorophytes • Unikonts - includes animals, fungi, and some protists; 2 major groups —amoebazoans —*opisthokonts: contain the protists most closely related to fungi and animals • why do we care about protists? —symbiotic protists —photosynthetic protists are producers and make up the foundation of food webs —algae form base of aquatic food web
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