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Chapter 23 Cellular organisms In one of two domains: Archaea and Eubacteria Generally smaller than eukaryotes Most are unicellular, some form colonies or filaments No membrane-enclosed organelles Ribosomes are located in the cytoplasm In some – the inner plasma membrane is extensively folded inward to provide reaction sites Most have a cell wall Cocci – spherical • Single cells • Groups of two: diplococci • Long chains: streptococci • Clumps: staphylococci Bacilli – rod-shaped • In single rods or long chains Spiral: • Spirochete – flexible spiral • Spirillum – rigid spiral Vibrio – spirillum shaped like a comma Provides shape and stability Allows the cell to inhabit hypotonic surroundings without bursting Does not help in hypertonic solutions – most bacteria do not grow well in foods preserved with high sugar or salt content In eubacteria the cell wall contains peptioglycan Gram-positive bacteria: • Appear blue or violet • Cell walls with a very thick layer of peptidoglycan • Disease causing gram-positive bacteria are easily killed by penicillin which interferes with peptidoglycan production Gram-negative bacteria: • Appear red or pink • Cell walls have two layers: a thin peptidoglycan layer and a thick outer membrane Capsule – a slime layer that surrounds the cell wall in some species • May provide pathogenic bacteria protection • May also allow some bacteria to attach to surfaces (e.g.: to cause dental plaque) Pili – short, hair-like projections of protein which allow bacteria to adhere to each other or other surfaces Flagella – longer projections found in mobile bacteria In cytoplasm, not surrounded by a membrane In most, a singular circular chromosome Most bacteria also contain smaller circular plasmids which may contain genes that code for enzymes, genetic exchange, or antibiotic resistance Asexual: • Binary fission – DNA replication followed by a transverse wall separating the two new cells • Budding – a bulge forms and matures, eventually separating from the original cell • Fragmentation – walls develop within a single cell which then separates into several different cells Genetic exchange: • Transformation – fragments of DNA released by one cell are picked up by another • Transduction – a phage (form of a virus) carries bacterial DNA from one to another • Conjugation – two different bacterial cells exchange genetic material Some bacterial form dormant, extremely durable cells in response to unfavorable environmental conditions Tetanus, gas gangrene, anthrax can all form endospores Heterotrophs – most bacteria obtain energy from surroundings: • Chemoheterotrophs – decomposers and pathogens • Photoheterotrophs – get carbon from other organisms but have chlorophyll to trap sunlight energy Autotrophs – manufacture their own organic molecules • Photoautotrophs – use photosynthesis • Chemoautotrophs – use chemosynthesis Archaea: • No peptidoglycan in cell walls • Many live in extremely harsh environments: no oxygen, high salt, or high temperatures Eubacteria: • Peptidoglycan in cell walls • Widely distributed and better known Decomposers • Recycle chemical nutrients necessary for life • Especially important in the nitrogen cycle Pathogens • Exotoxins - poisons produced by the bacteria that cause the damage • Endotoxins – components of the cell walls that affect the host only when released from the dead bacteria Food production • Microbial fermentation – yogurt, pickles, olives, sauerkraut, vinegar, soy sauce Antibiotic production Genetic engineering Bioremediation