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4/6/2015 Brief history of life on Earth 4.6 Billion Years ago: Earth forms 3.6 Billion Years ago : First life on the planet (Prokaryotes = Bacteria) 2.8 Billion Years ago : First eukaryotic life (also microbial – algae/protozoa) 0.4 Billion Years ago: First animals and plants (Fossil evidence indicates that modern humans originated in Africa about 200,000 years ago) Fossilized stromatolite * Stromatolites - layered rock-like structures formed in shallow water by the trapping/binding/cementation of sedimentary grains by microbes; Represent the most ancient records of life on Earth. 1 4/6/2015 Two types of Cellular Organization • Eukaryotic cells – DNA surrounded by a membrane/envelope =>cell nucleus • Prokaryotic cells – DNA not surrounded by an envelope Prokaryotic Structure Relatively simple structure: DNA, ribosomes, cell membrane, cell wall, plus a few other parts (not shown) 2 4/6/2015 Eukaryotic Structure By comparison, “euks” are much more complex, containing specialized organelles to perform particular functions Prokaryotes and eukaryotes: universal vs. distinct structures Universal: Both have DNA, ribosomes (to make proteins), and cell membranes “EUK” Eukaryotes have energy organelles (mitochondria / chloroplasts), an endomembrane system (ER/GOLGI) to package and sort materials, cytoskeleton (fibers that move materials around and help with cell division), and a nuclear membrane “PROK” 3 4/6/2015 How did we get from prok to euk ??? • Lynn Margulis “Endosymbiotic theory” • Euks came from proks ingesting other proks, but instead of digesting them they began to use them as organelles • Evidence shows that mitochondria and chloroplasts have bacterial origins “TAXONOMY” Biology attempts to catalog organisms 1. Aristotle: described 500 plants and animals 2. Linnaeus: described 1000’s of plants and animals, devised the binomial system (Genus/Species), part of the hierarchal system of nomenclature 3. Whittaker: 5 Kingdom system (Animals/Plants/Fungi/Protista/Bacteria) 4. Woese: 3 Domain System 4 4/6/2015 Nomenclature gives scientific names to organisms • Linnaeus’ Binomial system: everything has two names based on genus and species (e.g. homo sapiens) • His groupings were based upon shared physical characteristics. Quoted as saying “GOD CREATES, LINNAEUS NAMES” Whittaker’s Five Kingdom System 1. 2. 3. 4. Animals Plants Fungi Protists (algae/protozoa/ + “lower fungi”) 5. Monera (prokaryotes) Note that 4 out of 5 are eukaryotic organisms, only 1/5 prokaryotic 5 4/6/2015 The three-domain system places the Monera in separate lineages Classification is based on differences in ribosomal RNA (and/or the DNA genes that encode these RNAs) Carl Woese Recall that all life forms have ribosomes, so by comparing how similar the ribosomes are to each other we can see how closely they are related to one another Comparison of rRNA genes from diverse organisms Note that certain regions of the sequences vary from each other, so that the more similar they are, the more closely related are the organisms (more differences = more distant relationship) 6 4/6/2015 Relationship between diverse organisms based on sequences of rRNA genes Organisms A and B have only 2 differences between them, whereas both A+B have 6 differences from C: thus it is inferred that A+B should be closer together on a family tree than either should be to organism C (note that “X” is the universal ancestor of all three other organisms) Three Domain System THE THREE DOMAINS ARE: EUBACTERIA, ARCHAE, and EURKARYA (thus 2/3 PROKS and 1/3 EUKS) 7 4/6/2015 Eubacteria COMPARISON OF Eubacteria Archae Eukaryotes THIS HIGHLIGHTS THE DIFFERENCES BETWEEN THE 3 DOMAINS Source: S. Finkel, 2002 Eubacterial vs. Archaeal cytoplasmic membranes ARCHAE cell membrane is much stronger with more molecules and tighter bonding than EUBACTERIA -- this helps them to survive extreme environments 8 4/6/2015 Bacteria: Shapes and Arrangements Bacilli Cylinder shape Can be singles or form chains Examples: E. coli, Shigella, Salmonella, Anthrax, etc. 9 4/6/2015 Cocci CUBE OF 8 = Sarcina Examples: “Staph” infections, Strep throat bacteria, etc. Spirals and other shapes Spirilla are thick and rigid, with a single flagellum at each end; Spirochetes are thin and flexable, with an internal flagella called an “axial filament” that rotates beneath the cell wall (moves like a “cork screw”) 10 4/6/2015 Bacteria: Structure From the outside to the inside of the cell…………… Bacterial flagella Provide motility Rotate (clockwise/countercwise) Embedded in cell wall, extend out from there Allow bacteria to move toward nutrients, or away from repellants (e.g. antibiotics, white blood cells) – this is called “chemotaxis” 11 4/6/2015 Structure of bacterial flagella Basal body = “motor” embedded in the cell wall and membrane; Rotates, which then drives the external filament Bacterial motion mediated by flagella If the flagella rotate counterclockwise, the bacterium moves in a straight path (“run”) if they rotate clockwise, the bacterium will tend to stay in place (“tumble”) 12 4/6/2015 “Chemotaxis” For example: If bacteria encounter food, the organisms stay around the same area (see “A” above). However, if food is sensed somewhere nearby, they’ll move toward it (see “B”). Movement of Shigella within and between cells Note that these organisms invade intestinal cells and then move from one cell to another, causing “water loss” = extreme diarrhea 13 4/6/2015 TYPES OF FLAGELLA Monotrichous: one flagellum at one end Amphitrichous: flagella at both ends Lophotrichous: two or more flagella clustered at one end only Peritrichous: many flagella all around the cell Pili Protein fibers Help bacteria to attach to surfaces (e.g. urethra in Urinary tract infections) Special pili (conjugation pili) are used for bacteria “intercourse” where they move DNA between cells Enhance ability to cause disease 14 4/6/2015 Binding of pili to host cells Note that the tips of pili contain proteins that dock down and lock on to receptor molecules on host cell surfaces Glycocalyx Sticky, sugary layer around cells Not all bacteria have it, but the ones that do are more dangerous! Attachment is easier (sticky) Retain water, so they don’t dry out Repel the white blood cells of the immune system as WBCs are keyed to look for foreign proteins so these sugars help hide the cell 15 4/6/2015 Two types: Cell wall 1. Gram-positive: thick layer of peptidoglycan (surrounds cells and protects them); also contains teichoic acid; Retains the primary (purple) gram stain in spite of gram alcohol (destaining) treatment. 2. Gram–negative: thin layer of peptidoglycan, lose the gram stain when gram alcohol (destainer) is applied. ** Also have an extra membrane outside the cell wall called LPS (lipopolysaccharide) layer – contains endotoxin, an ‘internal’ poison that makes these cells dangerous (re: septic shock) Structure of Gram-positive cell envelope Note the thick peptidoglycan and the Teichoic acid that binds together the cell wall components 16 4/6/2015 Structure of gram-negative cell envelope Note the thin peptidoglycan sandwiched between two membranes, as well as the lack of teichoic acid This part contains endotoxin Cell envelope of Gram-Positive vs. Gram-Negative Bacteria Hint: Make sure you can compare and contrast these two for an exam ! 17 4/6/2015 Structure of E. coli peptidoglycan Synthesis of peptidoglycan 18 4/6/2015 b-lactam antibiotics Prevent new cell walls from being formed so bacs burst apart (below) ! Cell membrane Permeability barrier (cellular materials separate from environment); imports specific nutrients, exports waste, site of ATP production in bacs Chemical composition: 40% phospholipids 60% embedded proteins … Both move (Fluid mosaic model) Action of disinfectants/drugs: alcohols dissolve this layer; some Anti-biotics poke holes in it 19 4/6/2015 Cytoplasm Is the center of biochemical activity Structures within the cytosol --Ribosomes --Inclusion bodies: store nutrients (Phosphate/Sulfur/Glycogen) --DNA: two forms A. Chromosome(s) B. Plasmids = molecules of DNA separate from chromosome that can carry genes for toxins or antibiotic resistance Spores Are designed for dormancy Spore formation: when nutrients are limited Chemical composition: chromosome + small amount of cytoplasm surrounded by thick layers of peptidoglycan Resistance: little water so heat resistant; Dipicolinic Acid stabilizes the DNA Can survive alcohol, boiling water, etc for many years Many Pathogenic bacteria form spores including Anthrax, Botulism, and Tetanus bacteria 20 4/6/2015 Bacterial Spore Formation When nutrients are available, the spore will germinate back to a normal cell again 21