Presentation on theme: "4/22/2015 Prokaryotes. 4/22/2015 Prokaryotes 1.The World of Prokaryotes. 2.Structure, Function, and Reproduction of Prokaryotes. 3.Nutritional and Metabolic."— Presentation transcript:
4/22/2015 Prokaryotes 1.The World of Prokaryotes. 2.Structure, Function, and Reproduction of Prokaryotes. 3.Nutritional and Metabolic Diversity.
4/22/2015 The History The story of over 3.5 billion years. Dominate the biosphere. Leave in almost all conditions. Essential to all life on Earth: decompose dead organisms and return vital chemicals to the environment. Leave in symbiotic relationships (mitochondria and chloroplasts evolved from prokaryotes). Although only 5000 species are known, the estimates are in the range of about 400 000 to 4 million.
4/22/2015 Eukaryotic versus prokaryotic cells Major differences The presence of nucleus; Internal membrane – subdivision into many different organelles in eukaryotes; Simpler genome, separation of the genetic material – DNA into nucleus in eukaryotes. Cell wall of prokaryotes has different composition and structure
4/22/2015 The world of prokaryotes Carl Woese from the University of Illinois first recognized the distinction between bacteria and archaea Archae: Believed to have evolved from the earliest cells Inhabit extreme environments Bacteria: Considered the more “modern” prokaryotes, having evolved later More numerous Differ from Archae in structural, biochemical, and physiological characteristics That is how taxonomic level above kingdom called domain has appeared.
4/22/2015 The three major lineages of life Domains Eukarya and Archaea share a common ancestor that lived more recently than the ancestor common to archaea and bacteria. Molecular studies support hypothesis that the archaea are more closely related to eukaryotes than they are to bacteria.
4/22/2015 Three Domains and Five Kingdoms Monera PlantaeProtista AnimaliaFungi All prokaryotic organisms, including Bacteria and Archaea Unicellular eukaryotes and simple multicellula r relatives Domain Eukarya Domain Bacteria Domain Archaea Defined by nutritional mode, they absorb nutrients after decomposing organic material Carry out photosynthes is Multicellular eukaryotes that ingest other organisms
4/22/2015 Bacilli Rod-Shaped Bacterium, hemorrhagic E. coli, strain 0157:H7 (division) (SEM x22,810). This image is copyright of Dennis Kunkel
4/22/2015 Cocci Coccoid-shaped Bacterium (causes skin infections), Enterococcus faecium (SEM x33,370). This image is copyright of Dennis Kunkel
4/22/2015 Helices Left, Borrelia burgdorferi, the organism that causes Lyme disease; Right, Treponema pallidum, the spirochete that causes the venereal disease syphilis.
4/22/2015 Cell wall structure Cell wallsCell walls of bacteria contain peptidoglycan instead of the cellulose found in cell walls of plants and some algae. cellulose
4/22/2015 Cell wall function Maintain the cell shape Protect the cell Prevent the cell from bursting in hypotonic environment Differ in chemical composition and construction from the cell walls of protists, fungi, and plants.
4/22/2015 Cell wall Most bacterial walls contain peptidoglycan (ptg): polymers of modified sugars cross-linked by short polypeptides. Based on differences in their wall structure many members of the domain Bacteria can be separated into two groups: - gram-positive, have simpler walls, with a large amount of ptg; - gram-negative, more complex with less ptg, the outer membrane contains lipopolysacharides, carbohydrates bonded to lipids.
4/22/2015 Cell wall The outer membrane is often toxic and protect the pathogen against host defence and antibiotic penetration. Lipopolysaccharides impede entry of drugs into the cells, making gram-negative bacteria more resistant to antibiotics That is why, among disease-causing bacteria, gram- negative are more threatening. Many penicillin-like antibiotics selectively target only bacteria by preventing the cross-link in ptg.
4/22/2015 Cell wall Many prokaryotes secrete sticky substances that form an additional protection layer – capsule outside the cell wall. Some prokaryotes adhere to one another or to substrate by surface appendages called pili.
4/22/2015 Pili E. coli with fimbriae (TEM x17,250) Function in: -attaching to surfaces or to other prokaryotes; -during conjugation help to hold partners together while DNA is transferred.
4/22/2015 Many prokaryotes are motile Half of all eukaryotes are capable of directional movement. Most common mechanism of movement is flagellar action. Flagella may be scattered over entire surface or be either from both ends or from one.
4/22/2015 Difference from eukaryotic flagella Unique in structure and function; lack the “9+2” microtubular structure and rotate rather than whip back and forth like eukaryotic flagella Not covered by extension of plasma membrane Only 1/10 the width of eukaryotic flagella
4/22/2015 Many prokaryotes are motile Second – spirochetes-type of motility: bacteria has several helical filaments under the outer membrane with the basal motor attached at one or other end of the cell; rotation of the filaments forces the flexible cell to move like a corkscrew.
4/22/2015 Many prokaryotes are motile Third, some prokaryotes secrete slimy chemicals and move by gliding motion that may result from the presence of flagellar motors that lack flagellar filaments.
4/22/2015 Many prokaryotes are motile Many prokaryotes are capable of taxis, movement toward or away from a stimulus. Chemotaxis – response to chemical stimuli, toward food or oxygen (a positive chemotaxis) or away from some toxic substances (a negative chemotaxis).
4/22/2015 The cellular and genomic organisation Bacteria lack a nuclear membrane and membrane-bound organelles. Biochemical processes that normally occur in a choloroplast or mitochondrion of eukaryotes will take place in the cytoplasm of prokaryotes. choloroplastmitochondrion
4/22/2015 The cellular and genomic organisation Bacterial DNA is circular and arrayed in a region of the cell known as the nucleoid.nucleoid Scattered within bacterial cytoplasm are numerous small loops of DNA known as plasmids.plasmids Bacterial genes are organized in by gene systems known as operons.
4/22/2015 EM of Neisseria gonorrhoeae Note the nucleoid region (n) where DNA is located as well as the electron dense areas of the cytoplasm (dark areas) on these two cells of Neisseria gonorrhoeae.
4/22/2015 Rapid growth and adaptation Asexual reproduction – binary fission leads to the formation of a colony of identical offspring. Without meiosis prokaryotes loos an important source of genetic variation.
4/22/2015 Rapid growth and adaptation However, they have three different mechanisms of genetic recombination: - transformation – genes are taken from the surrounding environment; - conjugation – direct gene transfer from one prokaryote to another; - transduction – the gene transfer by viruses. All these are unilateral DNA transfer.
4/22/2015 Rapid growth and adaptation Mutation is the major source of genetic variation in prokaryotes. Because of the short generation time favourable mutation would be propagated to a large number of the offspring. Without limiting resources, the growth of prokaryotes is geometrical 2 – 4 – 8 – 16 - … They stand extreme conditions and many of them release antibiotics to inhibit the growth of the other microorganisms and to compete for space and nutrients.
4/22/2015 Endospore formation Certain bacteria will form a spore within their cell membrane (an endospore) that allows them to wait out deteriorating environmental conditions. Certain disease causing bacteria (such as the one that causes the disease Anthrax) can be virulent (capable of causing an infection) 1300 years after forming their endospore!
4/22/2015 Nutritional and Metabolic Diversity Nutrition for bacteria is the way of obtaining energy and source of carbon for synthesis of organic compounds. Phototrophs use light as energy source. Chemotrophs obtain their energy from chemicals taken from the environment. Autotrophs use only inorganic CO 2 as a carbon source. Heterotrophs requires at least one organic nutrient – glucose.
4/22/2015 Nutritional and Metabolic Diversity Combination of the phototroph-versus-chemotroph (energy source) and autotroph-versus-heterotroph (carbon source) allows grouping prokaryotes to four major modes of nutrition: 1. Photoautotrophs – photosynthetic organisms that use light energy to synthesize organic compounds from CO 2 – cyanobacteria and plants.
4/22/2015 Nutritional and Metabolic Diversity 2. Chemoautotrophs – need only CO 2 and obtain energy by oxidizing inorganic substances (H 2 S, NH 3, Fe 2+ ) – unique to prokaryotes. 3. Photoheterotrophs – use light energy to obtain their carbon from organic form – unique to certain prokaryotes. 4. Chemoheterotrophs – consume organic molecules for both energy and carbon – wide range of prokaryotes, fungi, animals, plants.
4/22/2015 Chemoheterotrophs are the majority This category includes saprobes, decomposers that absorb their nutrients from dead organic matter, and parasites, which absorb their nutrients from body fluids of living hosts. Some of them are very strict in the requirements of the conditions: fool complex of amino acids, several vitamins, organic compounds – genus Lactobacillus; some of them are less particular, like E. coli which can grow basically on everything if only glucose is present.
4/22/2015 Nitrogen metabolism Diverse prokaryotes are able to metabolise most nitrogenous compounds. Nitrosomonas convert NH 3 into NO 2+. Pseudomonas convert NO 2+ or NO 3+ into N 2 gas. Some cyanobacteria are able to use N 2 from the air as a source of nitrogen – nitrogen fixation (N 2 to NH 3 ). They require CO 2, N 2, H 2 O and some minerals in order to grow.
4/22/2015 Oxygen metabolism Obligate aerobes use O 2 for cellular respiration and can not grow without it. Facultative anaerobes use O 2 but also can grow by fermentation in anaerobic environment. Obligate anaerobes are poisoned by O 2. Some of them live exclusively by fermentation, another extract chemical energy by anaerobic respiration.
4/22/2015 Reading Campbell et al. Biology. Ch. 27 (556-565)