Chapter 27 Bacteria and Archaea 1 Chapter 27 Bacteria and Archaea Masters of Adaptation of seawater In the summer parts of Utah s Great Salt Lake turns pink and the salt concentration can reach 32 nearly ten times that The pink color in the Great Salt Lake comes from trillions of prokaryotes in the domains Archaea and Bacteria including the archaea in the genus Halobacterium Halobacterium are species that thrive in salinities that dehydrate and kill other cells It compensates for water lost through osmosis by pumping potassium ions into the cell until the ionic concentration inside the cell matches the concentration outside Prokaryotic specie are also very well adapted to more normal habitats the lands and waters in which most other Their ability to adapt to a broad range of habitats helps explain why prokaryotes are the most abundant organisms on species are found earth Concept 27 1 Structural and functional adaptations contribute to prokaryotic success The first organisms to inhabit Earth were likely prokaryotes Most prokaryotes are unicellular although the cells of some species remain attached to each other after cell division They are well organized achieving all an organism s life functions within a single cell A key feature of nearly all prokaryotic cells is the cell wall which maintains cell shape protects the cell and prevents it Cell Surface Structures from bursting in a hypotonic environment inhibit cell reproduction polypeptides in cell wall composition dye In a hypertonic environment most prokaryotes lose water and shrink away from their wall Water loss can In eukaryotes that have cell walls such as plants and fungi the walls are usually made of cellulose or chitin Most bacterial cell walls contain peptidoglycan a polymer composed of modified sugars cross linked by short Archaea cell walls contain a variety of polysaccharides and proteins but lack peptidoglycan Using a technique called Gram stain scientists can classify many bacterial species into two groups based on differences Samples are first stained with crystal violet dye and iodine rinsed with alcohol and finally stained with a red Gram positive bacteria have simpler walls with a relatively large amount of peptidoglycan Gram negative bacteria have less peptidoglycan and are structurally more complex with an outer membrane that contains lipopolysaccharides carbohydrates bonded to lipids Gram negative bacteria tend to be more resistant than gram positive species to antibiotics because the outer membrane impedes entry of the drugs However certain gram positive species have virulent strains that are resistant to one or more antibiotics The cell wall of many prokaryotes is surrounded by a sticky layer of polysaccharide or protein this layer is called a capsule if it dense and well defined or a slime layer if it is less well organized Chapter 27 Bacteria and Archaea 2 These sticky layers allow prokaryotes to adhere to their substrate or to other individuals in the colony Some capsules and slime molds protect against dehydration or shield pathogenic prokaryotes from attacks by their host s immune system Some prokaryotes stick to one another using hair like appendages called fimbriae Fimbriae are usually shorter and more numerous than pili appendages that pull two cells together prior to DNA transfer from one cell to another Motility About half of all prokaryotes are capable of taxis a directed movement toward or away from a stimulus Among prokaryotes bacterial and archaeal flagella are similar in size and rotation mechanism but they are composed of different proteins Since the flagella of organisms in the three domains perform similar functions but probably are not related by common descent it is likely that they are analogous not homologous structures Evolutionary Origins of Bacterial Flagella kinds of proteins Bacterial flagellum have three main parts the motor hook and filament that are composed of 42 different Only half of the flagellum s protein components appear to be necessary for it to function the others are inessential or not encoded in the genomes of some species Of the 21 proteins required by all species studied to date 19 are modified versions of proteins that perform other tasks in bacteria The two other proteins in the motor are homologous to proteins that function in ion transport The proteins that comprise the rod hook and filament are all related to each other and are descended from an ancestral protein that formed a pilus like tube This suggests that bacterial flagellum evolved as other proteins were added to an ancestral secretory system descent with modification Exaptation is a process in which existing structures take on new functions through Internal Organization and DNA Prokaryotic cells lack the complex compartmentalization found in eukaryotic cells Some prokaryotic cells have specialized membranes that perform metabolic functions these membranes are In the majority of prokaryotes the genome consists of a circular chromosome with many fewer proteins than that found usually infoldings of the plasma membrane in the linear chromosome of eukaryotes Prokaryotes lack a membrane bounded nucleus their chromosome is located in the nucleoid a region of cytoplasm that appears lighter than the surrounding cytoplasm A typical prokaryotic cell may also have much smaller rings of independently replicating DNA molecules called plasmids most carrying only a few genes DNA replication transcription and translation are fundamentally similar processes in prokaryotes and eukaryotes Prokaryotic ribosomes are slightly smaller and differ in their protein and RNA content compared to Chapter 27 Bacteria and Archaea 3 eukaryotes Reproduction and Adaptation Prokaryotes are highly successful in part because of their potential to reproduce quickly in a favorable environment By binary fission a single prokaryotic cell divides into 2 cells then 4 8 16 and so on The cells eventually exhaust their nutrient supply poison themselves with metabolic wastes face competition from other microorganisms or are consumed by other organisms Reproduction in prokaryotes draws attention to three key features in their biology They are small They reproduce by binary fission They have short generation times Some prokaryotes are able to withstand harsh conditions making them more successful Certain bacteria develop resistant cells called endospores when they lack an essential nutrient The original cell produces a copy of its chromosome and