Prokaryotes AP Biology Spring 2011

 Domains the two domains of prokaryotes  Describe the unique characteristics of prokaryotes and their metabolic diversity  Discuss how prokaryotes reproduce  Give examples of positive and negative impacts of bacteria on humans

Viruses

 Read chapter  Good refresher on viruses  Remember:  Structure  Viral replication iral_infection_and_replication&video_id=50887

Viroids and Prions

 Since the 1970’s about 30 viroids have been identified  A viroid is a small circle of RNA that can affect organisms  Most affect plants; only one viroid known to affect humans  Prions are misfoldings of proteins  Accumulate in nervous system cells  Cause cell death and a spongiform pathology in the brain cell

Prokaryotes- Enduring, Abundant, and Diverse

 The earliest cells were prokaryotes, cells with no nucleus

 Bacteria:  Classified based on shape, cell wall properties, metabolism, and other properties

 Automated gene sequencing has elucidated prokaryote diversity  Shortly after life began there was a branching between bacteria and Archae  Which eventually led to Eukaryote lineage  Despite estimates of millions of species of bacteria, only about 5,000 named

 Bacteria are very successful and terms of reproduction  Metabolic diversity is key to reproductive success in bacteria

 Metabolic diversity:  Photoautotrophs are photosynthetic Cyanobacteria  Chemoautotrophs use electrons that they strip from inorganic compounds and use that energy to build organic compounds from CO2 and water

 Photoheterotrophs use light energy and obtain carbon from organic compounds from their environment  Chemoautotrophs get both their carbon and their energy by breaking down organic compounds This group includes many prokaryotes, some protists, and all animals and fungi Usually parasites- get butrients from living host

Prokaryotic Structure and Function

 Modern prokaryotes include bacteria and archeans  They are unicellular and do not enclose their DNA in a nucleus  All prokaryotes have ribosomes  Some have infoldings of their membrane  Nearly all have a cell wall, some have an external slime coat that helps them adhere to surfaces

 Gram staining: can identify many bacteria species by their wall staining properties  Unknown species exposed to purple dye, then iodine, then alcohol wash, and finally a counterstain  Gram-positive: stays purple  Gram-negative: loses colour at first, then counterstain turns it pink

 Glycocalyx: sticky mesh, consists of polysaccharides, polypeptides, or both  Capsule: when highly organized and attached firmly  Slime layer: when less organized, and loosely attached

 Three basic shapes:  Coccus: Spherical  Bacillus: Rod Cylindrical  Spirillum: Helical

 Two kinds of filamentous structures may be attached to the cell wall  Bacterial flagellum: rotates like a propeller to pl the cell along  Pili: help bacteria attach to another in conjugation (exchange of DNA), or help them attach to surfaces

 Reproductive rates in prokaryotes are high, some species can reproduce every 20 minutes  Some species reproduce using a budding mechanism  More commonly, reproduce with fission that is similar to mitosis

 Some bacteria can also pass along genes without reproducing  During conjugation a plasmid, a small, self- replicating circle of DNA containing only a few genes, can be passed to another cell

 Some F (fertilty) plasmids allow bacteria to engage in bacterial conjugation in which a pilus joins two prokaryotic cells to permit the transfer of plasmid DNA

Prokaryotic Growth and Reroduction

 When a bacterium divides, each daughter cell inherits a single chromosome  Circular double-stranded DNA molecule  Bacteria reproduce by prokaryotic fission  Results in two genetically identical daughter cells  Only bacteria and archaens reproduce by this type of cell division

 A plasmid is small, self-replicating circle of DNA containing only a few genes  Some F (fertility) plasmids allow bacteria to engage in bacterial conjugation in which a pilus joins two prokaryotic cells to permit transfer of plasmid DNA

 Conjugation

The Bacteria

 Thermophiles exist in extreme environments  Members of the genus Aquifex include bacteria that live in volcanic spring, thermal vents, and hot springs

 Chloroplast-containing bacteria  Anabaena: by means of heterocysts, can fix nitrogen

 Make up largest, most diverse bacterial group (gram negative)  Theiomargarita namibiensis:  Chemeoautotroph that lives in marine environments and gets its energy from striping electrons from sulfur  Rhizobium: fixes nitrogen on roots of legumes

 E. Coli & H. Pylori:  Live in human digestive system  E. Coli 

 Some free living, chemoautotrophic proteobacteria exhibit complex behavior  Magnetoacteria: attracted by magnetic fields  Myxobacteria: move as a group and feed on soil bacteria

 Gram Positive:  Not a monophyletic group If all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group  Most are chemioheterotrophs with thick cell walls that retain gram stain

 Lactobacillus: used in dairy product conversions such as yogurt  L.acidophilus: lowers the pH of skin and vaginal linings  Some form resistant endospores that can survive harsh environmental conditions  Ex. Clostridium tetani (tetnus) Tetnus

 Spirochetes: resemble a spring  Resposible for causing Lyme disease  Free living parasites or symbionts  Clamydias: intracellular parasites that affect animal cells  Cannot make DNA, pilfer it from cells

Archaeans

 Archaeans: differ in their ribosomal DNA and cell walls  Resemble eukaryotic cells by making histones and sharing the same start codon for transcription  Some may resemble first cells on Earth  Recently this group has been subdivided into 3 major groups

 Methane makers  Inhabit swamps, mud, sewage, and animal guts  Make ATP anaerobically by converting carbon dioxide and hydrogen to methane  Free oxygen kills them

 Salt lovers  Can tolerate high salt environments such as brackish ponds, salt lakes, volcanic vents on seafloor, and the like  Most are heterotrophic aerobes, some can switch to a special photosynthesis, using bacteriorhodopsin to produce ATP  Light activating pigment embedded in plasma membrane, when it absorbs sunlight energy, changes shape and pumps H+ out from cell. H+ flows back into it, through ATP synthase and drives ATP formation

 Heat lovers  Live in hot springs and other very hot places such as thermal vents of the sea floor where temps exceed 250 degrees C  Use sulfur as source of electrons for ATP formation