Bacteria and Archaea a The Prokaryotic Domains i Domain is broader than a kingdom Tree of Life a The tree of life has three main branches domains Eukarya Bacteria and Archaea The Bacterial Cell a b c d No organelles Single chromosome containing entire genome Plasma membrane Cell Wall i Peptidoglycan 1 Molecule distinct to bacteria 2 Antibiotics often prevent these from doing their job Although a bacterial cell is small bacteria outnumber eukaryotic cells on present day Earth by several orders of magnitude Bacteria have no membrane bound nucleus no energy producing organelles and no sex these are defining features of eukaryotic cells A bacterial cell s DNA is present as a single circular chromosome and a bacterial cell can carry additional DNA in the form of plasmids Since the DNA is not separated from the cytoplasm within a nucleus like in the eukaryotic cell transcription and translation both occur in the same location Cellular processes are carried out in the cytoplasm or in the membrane of a bacterial cell by proteins that are free floating or membrane bound The bacterial cell is supported by a cell wall made of peptidoglycan a polymer of sugars and amino acids I II III b e f g h i j k IV Prokaryotic Shapes Sizes a Most bacterial cells are small spheres rods spirals or filaments b Bacterial cells are small 200 nm 2 micrometers The reason they are so small is because they obtain nutrients by diffusion By being small the cell has a large surface area in proportion to its volume and this allows the interior parts of the cell to be close to their surrounding environment As a cell increases in size it is harder to supply it with the materials needed for growth just by diffusion alone Bacterial cells are commonly found as spheres rods spirals or filaments Volume increases much faster than surface area Cell wall is rigid Limited Surface area vs Volume ratio g h i Thiomargarita namibiensis a b Most of the cell is filled with a large vacuole One of the largest bacteria V Cytoplasm is a thin film around the periphery i The largest known bacteria cell is Thiomargarita namibiensis It s total volume is 100 million times larger than that of E coli However a large portion of its volume 98 is taken up by a vacuole so the cell s functions are restricted to a thin area around the cell s periphery similar to the same area of most other bacterial cells Typically bacteria are single celled organisms VI Myxobacterium a Some bacteria are multicellular forming simple filaments or sheets of cells b More unusual are myxobacteria which aggregate to form multicellular reproductive structures that are composed of several distinct cell types c d e f c d e f c VII Horizontal Gene Transfer reproduce asexually a Bacterial genomes are smaller than eukaryotic genomes b A process by which bacteria obtain new genes from other bacteria genetic diversity c Three methods i Conjugation ii Transformation iii Transduction Viruses d Bacterial genomes are small and lack the noncoding DNA characteristic of eukaryotic chromosomes growth e Their small size allows them to reproduce rapidly when their local environment is ideal for f Despite their small size however their genomes are diverse g This variation is possible because while most of their genes come from the parent cell they are also able to obtain new genes by horizontal gene transfer h Horizontal gene transfer allows bacterial cells to gain beneficial genes from organisms i j distributed throughout the bacterial domain and beyond Bacteria therefore are not the poor cousins of eukaryotes unable to generate genetic diversity by sexual recombination Instead bacteria have highly efficient mechanisms for adding and subtracting genes that permit them to evolve and adapt rapidly to local conditions k Perhaps the most widely discussed and worrisome manifestation of horizontal gene transfer is the rapid spread of antibiotic resistance among bacteria Chapter 48 a Antibiotic resistance genes b Used in the laboratory c Some bacteria are able to share genetic information through a process called conjugation d Here the bacterial cell synthesizes a thin strand of membrane bound cytoplasm pili that e This process can transfer plasmids from one cell to another allowing a cell to share such connects to other cells genes as antibiotic resistance VII Conjugation f g c VIV Transformation a Genes can also be transferred from one cell to another without any direct bridge between them If DNA is released into the environment by cell breakdown it can be taken up by other cells b Discovered when harmless strains of bacteria causing pneumonia could be transformed into disease causing strains through exposure to dead cells of the virulent strain I Transduction a b c Sometimes genetic material from the bacterial host is incorperated into the viral DNA upon assembly of the particles A third type of horizontal gene transfer can be found in viruses Here viruses that have infected bacterial cells can integrate their DNA into the host bacterial cell and persist within the cells as they grow and divide Before leaving the bacterial host the viral DNA removes itself sometimes taking additional host DNA with it which is then incorporated into the viral DNA Not immune to mutation e f Which type of horizontal gene transfer used by bacteria involves viruses d i ii iii Conjugation Transduction Transformation g What limits the size of cells i ii iii iv Flexibility of chromosomes Surface area to volume ratio Number of organelles it contains Number of ribosomes it contains h b c b c d II III No membrane bound organelles Single circular chromosome Cell size is limited by diffusion Characteristics of Archaea Extreme a b c d Membranes have a unique lipid composition compared to Bacteria and Eukaria e f g Many inhabit extreme environments An Expanded Carbon Cycle a No peptidoglycan Biochemistry is different Oxidation reduction chemistry i d e An extended Carbon Cycle Microbial Mats a IV Reactions in which electrons are removed from oxidation or added to reduction a molecule Reactions happen in pairs CO2 is reduced to carbohydrates ii Photosynthesis i Respiration i ii In all known photosynthetic eukaryotes photosynthesis is oxygenic O2 producing Respiration in most eukaryotic cells is aerobic uses O2 NOT ALL MOST O2 serves as an electron acceptor Carbohydrates are oxidized to CO2 The ways in which Bacteria and Archaea gather carbon and harvest energy make them indispensable parts of nature They are capable of
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