Ch. 19-20 Notes
Ch. 19-20 Notes 012
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Date Created: 03/07/16
CH. 19 Single-Cell Organisms 19.1: Life Consists of Three Domains That Share a Common Ancestor All organisms have: - cell membranes (phospholipid bilayer), ribosomes (have catalytic properties) - common metabolic pathways (Ex: glycolysis) - Semiconservative DNA replication (one strand is template to be copied, other is daughter strand) - DNA that encodes proteins Three Domains of Life: Bacteria: peptidoglycan in cell wall, ester-linked membrane lipids; unbranched Archaea: ether-linked membrane lipids à enables survival in extreme conditions; branched membrane lipids (unsaturated à kinks à fluid) Eukarya: membrane-enclosed nucleus/organelles, ester-linked membrane lipids; unbranched Eukaryotes: (eukarya) unicellular or multicellular - Share a more recent common ancestor with archaea over bacteria - Mitochondria originated through endosymbiosis with a bacterium Prokaryotes: (bacteria, archaea) unicellular - Cells divide by binary fission instead of mitosis - Genetic material isn’t organized in a membrane-enclosed nucleus; circular DNA - Lack most membrane-enclosed organelles (mitochondria, Golgi apparatus, etc.) Classification of Bacteria Before DNA sequencing, classification was based on: shape, color, motility, nutritional requirements, sensitivity to antibiotics, cell wall structure Peptidoglycan: unique to bacteria; material within bacterial cell walls; meshlike structure - Antibiotics interfere w/ synthesis of peptidoglycan à “leaky” - Eukaryote cells don’t have it, so there is no harm done to human cells Gram Stain: differences in cell wall structure; used to group bacteria Gram-Positive: retains dye creating blue to purple color; larger peptidoglycan layer outside of cell membrane Gram-Negative: pink to red color; thin layer surrounded by inner/outer cell membrane Cell Shapes: - Coccus: Sphere; occur singly or in plates/blocks/clusters - Bacillus: Rods; can form chains/clusters - Spirillum: Spiral; can form chains/clusters - Others include filaments or branched filaments Sequencing of rRNA genes is used for phylogenetic studies: - rRNA was present in common ancestor of all life - All free-living organisms have rRNA - Lateral transfer of rRNA among distantly related species is unlikely - rRNA has evolved slowly Lateral Gene Transfer: genes in prokaryotes move sideways between species within a generation - Causes gene trees to not match organismal trees when sequenced - Genes causing adaptation that increases fitness are most likely to be transferred laterally - Ex: antibiotic resistance 19.2: Prokaryote Diversity Reflects the Ancient Origins of Life Bacterial Groups Low-GC Gram-Positives: (Firmicutes) low ratio of G-C to A-T nucleotide base pairs in DNA - Some are gram-negative or have no cell wall - One group produce heat-resistant resting structures called endospores, used to protect DNA (Ex: anthr - Mycoplasmas: lack cell walls, small in size/small genome High-GC Gram-Positives: (Actinobacteria) higher ratio of G-C to A-T nucleotide base pairs in DNA - G-C base pairs have triple bonds whereas A-T base pairs have double bonds; greater number of bonds translates into greater stability, helpful when under warmer environments - Branched system of filaments - Ex: most antibiotics are derived from them; tuberculosis Hyperthermophilic Bacteria: extremophiles that thrive under extreme conditions - Hadobacteria: can survive under both extreme cold/heat - Thermus aquaticus was source of thermally stable DNA polymerase that lead to the development of PCR, Taq 19.3: Ecological Communities Depend on Prokaryotes Biofilms: cells bind to surface and secrete sticky, gel-like polysaccharide matrix that traps others cells - Cells that form biofilms are increasingly difficult to kill - Pathogenic bacteria harm the immune system b/c biofilm is often impermeable to antibiotics Quorum Sensing: Prokaryotes communicate triggering activities such as biofilm formation - Secretes small molecules similar to hormones o When alone, they float away o When with others, molecule increases in proportion to cell number - Signal producing protein à signal receptor protein à group behavior of genes only successful when all cells participate in unison o Bacteria in humans first divide increasing population size then secrete hormones to talk to the rest of the population - Bacteria are multi-lingual o 2 enzymes create 2 different signals enables bacteria to count amount of itself/others o inter-species detects amount of “others”; intra-species detects amount of “self” o Uses to decide task based on majority/minority of population - Scientists use behavioral modification to stop communication o Competitive inhibitor blocks signal from binding to receptor, in hope to stop the formation of biofilms Bacterial infection depends on: 1. Invasiveness: pathogens ability to multiply in host’s body 2. Toxigenicity: ability to produce toxins Endotoxins: form inside bacteria and are released when Gram-neg lyse/burst; rarely fatal, cause fever, nausea, and diarrhea Exotoxins: soluble proteins released by living bacteria; highly toxic, sometimes fatal Metabolic Pathways Obligate Anaerobes: oxygen is poisonous Facultative Anaerobes: use both anaerobic/aerobic metabolic pathways Aerotolerant Anaerobes: not damaged by oxygen, but cannot use it Obligate Aerobes: need oxygen to survive Nutritional Categories of Organisms Photoautotrophs: perform photosynthesis using CO as car2on source - Cyanobacteria: uses chlorophyll a to produce O gas 2 - Others use bacteriochlorophyll to produce sulfur, not oxygen; can absorb light of longer wavelengths than the chlorophyll molecules enabling them to use light that goes unabsorbed by algae Photoheterotrophs: obtain energy through light, obtain carbon from organic compounds created by other organisms Chemoautotrophs: obtain energy by oxidizing inorganic substances using some energy to fix carbon Chemoheterotrophs: obtain energy/carbon from complex organic compounds that have been synthesized by other organisms (Ex: humans!) Most prokaryotes are decomposers: metabolize organic compounds from dead material to return to environment as inorganic substances - Some bacteria carry out electron transport without using oxygen as an electron acceptor, instead using nitrate, nitrite, or sulfate - Nitrogen is necessary in building proteins, but is difficult to process in its gaseous form Denitrifiers: release N 2as to atmosphere + Nitrogen Fixers: covert N ga2 into ammonia (NH ) maki4g it usable by organisms Nitrifiers: oxidize ammonia à nitrite ions à nitrate ions; Metabolism is powered by energy released by this oxidation Haber-Bosch Cycle: uses chemicals/pressure to convert nitrogen gas to usable nitrate ions; dependent on finite resource of petroleum as an energy source of this process CH. 20 The Origin & Diversification of Eukaryotes 20.1: Eukaryotes Acquired Features from Both Archaea and Bacteria Protists: Eukaryotes that aren’t plants, animals, or fungi - Many are asexual - Not a taxonomic group, instead a convenience term - Therefore, not all eukaryotes classified as protists form a monophyletic taxon Origin of Eukaryotic Cell: - Flexible cell surface - Cytoskeleton - Nuclear envelope - Digestive Vacuoles - Acquisition of certain organelles via endosymbiosis Flexible Cell Surface: - Loss of cell wall allows infolding à increased SA à increased gas/nutrient exchange - Makes endocytosis possible (cell pinches off pieces of environment to bring into cell) Changes in Cell Structure: - Develops complex cytoplasm - Ribosome-studded internal membranes form - DNA enclosed in nucleus - Flagellum forms from microtubules of cytoskeleton - Digestive vacuoles evolve Simple cytoskeletons most likely evolved from prokaryotes: - Increased development of filaments/microtubules supports cell and allows it to make changes in shape, to distribute daughter chromosomes, and to move materials throughout cell - Microtubules allow some cells to develop eukaryotic flagella - Most likely evolved from proteins due to homologs of cytoskeleton protein in prokaryotes??? Nuclear Envelope: - Early in evolution - Possibly from DNA attached to inner plasma membrane - Some evidence supports this based on similar shape of infoldings Phagocytosis: the ability to engulf and digest other small molecules/cells à advanced metabolism of eukaryotes Endosymbiosis: proteobacterium was incorporated/evolved in mitochondrion - Original function of mitochondrion was to detoxify oxygen produced by cyanobacteria by reducing it to water - Later decided this process is coupled with ATP production Primary Endosymbiosis: Gram-negative cyanobacterium engulfed by a larger eukaryotic cell - Cyanobacterium has both inner/outer membrane à original chloroplasts had two membranes - Remnants of peptidoglycan-containing cell wall are present in between chloroplast membranes of glaucophytes - Gave rise to the chloroplasts of red algae, green algae & land plants Secondary Endosymbiosis: - Eukaryote engulfed a small eukaryotic organism, green alga cell which became a chloroplast - Euglenoid chloroplasts have three membranes, same pigments as land plants/green algae Tertiary Endosymbiosis: Dinoflagellate lost its chloroplast and took up another protist that acquired its chloroplast through secondary endosymbiosis 20.2: Major Lineages of Eukaryotes Diversified in the Precambrian Eight major clades of eukaryotes à Five major groups of protist eukaryotes (w/ great diversity) - Microbial Eukaryotes: Unicellular species of protists - Some are multicellular/large (Ex: Giant kelp) Multicellularity has arisen many times in eukaryotes - Artificial selection for multicellularity can produce repeated, convergent evolution of multicellular forms in normally unicellular species - Many unicellular species retain individual identities while associating in larger multicellular colonies - There’s a continuum from unicellular to fully multicellular species Protists classified based on life histories/reproductive features - Today, electron microscopy/gene sequencing reveal more evolutionary patterns - Lateral gene transfer complicates efforts to reconstruct evolutionary history of protists Alveolates: sacs called alveoli lie beneath cell membrane that helps support cell surface - All are unicellular, most photosynthetic - Include dinoflagellates, apicomplexans, and ciliates Dinoflagellates: mostly marine, photosynthetic, primary producers of organic matter in oceans - Some species cause red tides - Some are endosymbionts w/ invertebrates, live within cells of another (Ex: corals) - Some are nonphotosynthetic parasites w/ various marine organisms Apicomplexans: obligate parasites w/ apical complex (mass of organelles at tip of cell that help invade host tissue) - Elaborate life cycles including asexual/sexual reproduction in different hosts Ciliates: numerous hair-like cilia (similar to eukaryotic flagella) - Complex body forms w/ two types of nuclei - Heterotrophic; few have photosynthetic endosymbionts - Provide precise locomotion - Contractile Vacuoles: freshwater protists use them to excrete excess water that is taken in through osmosis - Digestive Vacuoles: digests solid food protists ingest by endocytosis Stramenopiles: rows of tubular hairs on the longer of its two flagella Diatoms: unicellular, some associate in filaments, carotenoids give them a yellow/brown color - Only male gametes have flagella - Deposit silicon dioxide in two-piece cells walls w/ intricate patterns unique to each species - Reproduce sexually & asexually - Abundant in oceans/fresh waters & are major photosynthetic producers Brown Algae: brown color comes from carotenoid - All multicellular, marine - Composed of either branched filaments or leaflike growths - Attached forms develop holdfasts w/ acid to glue them to rocks (Alginic acid is an emulsifier used in ice cream/cosmetics) Oomycetes: water molds, downy mildews - Used to be classified as fungi (but they have cellulose in cell walls) - Absorptive Heterotrophs: secrete enzymes that digest large food molecules into smaller ones that can be absorped - All are aquatic & saprobic (feed on organic dead matter) Rhizaria: unicellular & mostly aquatic; long thin pseudopods; large component of ocean sediments Cercozoans: soil/aquatic organisms; one group has chloroplasts derived from green algae by secondary endosymbiosis (chloroplasts contain trace of alga’s nucleus) Foraminiferans: Secrete external shells of calcium carbonate - Threadlike branched pseudopods extend through holes in the shell and form a sticky net to catch smaller plankton - Accumulations of shells produced most of the world’s limestone Radiolarians: radial symmetry; thin stiff pseudopods reinforced by microtubules; marine - Secrete glassy endoskeletons - Pseudopods increase SA of cell helping it stay afloat Excavates: Diverse groups that split soon after origin of eukaryotes Diplomonads & Parabasalids: unicellular & lack mitochondria (derived condition) - Parabasalids have undulating membranes that aid in locomotion Heteroloboseans: amoeboid body form - Naegleria has two stages: one w/ amoeboid cells, one w/ flagellated cells - Some species enter human body and cause fatal diseases of the nervous system Euglenids & Kinetoplastids: mitochondria w/ disc shaped cristae & flagella w/ crystalline rod - Mostly reproduce asexually - Some euglenids are always heterotrophic; some photosynthetic but can lose pigments/feed on organic matter - Kinetoplastids are parasites w/ two flagella & mitochondrion w/ kinetoplast that has multiple circular DNA molecules - Trypanosomes are pathogens that change cell surface recognition molecules making them hard to control/kill Amoebozoans: amoeboid body w/ lobe shaped pseudopods Loboseans: feed on small organisms/particles of dead matter by engulfing them w/ pseudopods - Many live on bottoms of lakes/ponds - Most exist as predators, parasites or scavengers Plasmodial Slime Molds: multinucleate mass formed when nucleus of amoeba undergoes rapid mitotic division increasing cytoplasm/organelles - During vegetative state it exists as a wall-less mass of cytoplasm w/ multiple diploid nuclei - Coenocyte: many nuclei enclosed in a single cell membrane - Moves by cytoplasmic streaming while engulfing food particles by endocytosis - In unfavorable conditions, it becomes a hardened mass or a spore-bearing fruiting structure Cellular Slime Molds: (myxamoeba) single haploid nuclei; engulfs bacteria by endocytosis; reproduce by mitosis/binary fission - Amoeboid cells are the vegetative state - In unfavorable conditions, aggregates into slug or pseudoplasmodium which can migrate to form fruiting structure; individual myxamoebas retain cell membranes/identity 20. 3: Protists Reproduce Sexually and Asexually Asexual reproduction among protists: - Equal splitting of a cell into two by mitosis then cytokinesis - Splitting of one cell into multiple cells - Budding: outgrowth of new cell from surface of an old one - Sporulation: formation of specialized cells that can develop into new individuals Clonal Lineages: Offspring from asexual reproduction are genetically identical to parents Reproduction in Paramecium: - Two types of nuclei (one macronucleus, several micronuclei) - During asexual reproduction, all nuclei are copied before division of cell - Conjugation: two individuals fuse and exchange micronuclei; sexual process but not reproductive being that two cells begin process and two cells exist at the end of the process Alternation of Generations: life cycle found in multicellular protists, all land plants & some fungi - Multicellular diploid spore-producing organism gives rise to a multicellular, haploid, gamete- producing organism - Haploid organism, diploid organism, or both can also reproduce asexually - Heteromorphic: two generations differ morphologically - Isomorphic: two generations are similar (Both types occur among brown algae) - Gamete producing organism is already haploid and doesn’t undergo meiosis - Specialized cells of diploid organism (sporocytes) divide meiotically producing four haploid spores which eventually divide mitotically producing multicellular haploid generation which then produces gametes by mitosis/cytokinesis - Gametes fuse to produce diploid organism 20.4 Protists Are Critical Components of Many Ecosystems Phytoplankton are important Primary producers: - Diatoms performs 1/5 all carbon fixation on Earth - Gateway for energy from the sun to the rest of living world - Autotrophs eaten by heterotrophs Some microbial eukaryotes are pathogens - Plasmodium: parasites in red blood cells of humans; cause malaria; extracellular parasite in mosquito; intracellular parasite in human host - Some phytoplankton species of diatoms and dinoflagellates reproduce greatly under favorable conditions à Red Tide, toxins produced by them can kill vertebrates Many microbial eukaryotes live as endosymbionts in animal cells/radiolarians - Coral Bleaching: Some photosynthetic dinoflagellates are endosymbionts in corals; when dinoflagellates die the color becomes bleached; if corals don’t acquire new endosymbionts they will die or are damaged due to reduced food supply Reliance on remains of ancient marine protists: - Diatoms store energy as oil after dying and sinking to ocean floor - Diatomaceous earth is sedimentary rock composed on silica walls of diatoms; can be used for installation, filtration, metal polishing, to kill insects
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