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Scope of MicroBiology

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					The Scope of Microbiology
Cell theory There are three points to modern cell theory: •Cells are the basic unit of life •All living organisms are composed of one or more cells •All cells are derived from previously existing cells These points were derived by two early cell biologists, Schleiden and Schwann, in the 1840s, and are still used as our basic definition of life. Note that this does not take into account viruses, which do not have cellular structure. Viruses were unknown when cel theory was developed. Whether viruses are "alive" depends on how strictly the first two points of cell theory are interpreted. Many biologists think that there are strong arguments for including viruses among the living, but this is still a point of debate among biologists. Cell structure In a simplistic sense, cells consist of a cell membrane surrounding cell fluid, called cytoplasm. Within the cytoplasm are structures that carry out cell functions. These structures include chromosomes, where the information needed to construct the cell is stored ribosomes where the information stored in the chromosomes is made into proteins enzymes, which are proteins that allow the cell to carry out chemical reactions structural proteins, which give shape to cells Cell function Cells obtain energy from their environment, and use it to build and maintain their internal structure. Cells use the energy to concentrate nutrients and build the components they need to grow (increase in mass) and reproduce (divide)
Prokaryotes and Eukaryotes are cells cells: produce exact copies of themselves contain genetic imaterial (DNA) obtain and use energy are surrounded by a membrane maintain internal homeostasis

Cell types Based on their internal structure, cells can be divided into two major groups: Prokaryotic cells, which have a single chromosome and no internal membrane bounded structures. These cells are structurally simple, and are represented in the earlilest fossils known. Eukaryotic cells, which have many linear chromosomes and a vast array of internal specialized membrane bounded structures, including a nucleus, mitochondria, and a acomplex internal membrane system that is involved in synthesizing and processing proteins. Classification of cells Organisms alive today are classified according to cell and gene structure into three large groups. Two of these groups are prokaryotic: the Archaea, which are believed to represent the earliest organisms on earth: and the Bacteria, which includes most of the microorganisms we will study in this course.

The Eukarya, which includes all eukaryotes, include most of the organisms with which we are familiar: plants, animals, protists, and fungi. Molecular analysis of the genes encoding a very conservative kind of RNA, called ribosomal RNA (rRNA) indicate that the Archaea are as different from the Bacteria as Eukaryotes are.
Comparison of Bacteria, Archaea, and Eukaryotes Characteristic Bacteria Archea Cell membrane ester-linked straight ether-linked branched hydrocarbons hydrocarbons Cell wall muramic acid no muramic acid Cellular organelles No No Chromosomes one, circular one, circular Funny bases in tRNA Thymine and dihydrouridine no thymine or dihydrouridine Initator amino acid formyl methionine methionine Membrane-bounded nucleus no no Protein Synthesis sensitive yes No to Chlormphenicol, erythromycin, streptomycin Ribosomes 70S 70S RNA polymerase One type, different σ subunits several types Eukaryote ester-linked straight hydrocarbons no muramic acid yes multiple, linear Thymine and dihydrouridine methionine yes No (except mitochondria and chloroplasts) 80S (70S in mitochondria and chloroplasts) several types

Nomenclature Biologists have a system for naming each type of organism. It is based on the system developed by Karl von Linne (also known by his Latin name Carolus Linnaeus) Linnaeus tried to organize organisms into groups that reflected how closely related they were to each other. Today, we recognize six major groups of organisms: Archaea Bacteria Plants Animals Fungi Protists Of these, Archaea, Bacteria, Fungi, and Protists are traditionally studied in Microbiology. Linnaeus realized that all animals had certain characteristics in common, but that they could be divided into subgroups, for example that some animals have backbones and others don't. Animals with backbones could also be divided into subgroups: fish, amphibians, birds, reptiles, and mammals. All mammals have characteristics in common that they don't share with the other groups. By making additional subdivisions, he classified organisms according to a descending order: Kingdom Division (or Phylum) Class Order Family Genus Species

Humans, for example, are classified with Kingdom all animals Phylum animals with spinal cords Class all mammals Order all primates Family all hominids Genus Homo (Man) Species sapiens (wise) The scientific name for humans, Homo sapiens, is what we would use to identify ourselves taxonomically. All organisms have such a binomial nomenclature. There are a few rules about naming organisms. First, no two bacteria, for example, can have the same genus and species name. Only one bacterium can have the name Escherichia coli. Second, The genus name, which comes first, is always capitalilzed, and the species name always begins with a lower case letter. Escherichia Coli and escherichia coli are both incorrect. Third, since the names are considered to be Latin (a foreign language) they must be italicized or underlined when written. Escherichia coli is incorrect, but Escherichia coli and Escherichia coli are both correct. Types of microorganisms
Fungi all are saprobes of 10,000s of species, only about 55 are pathogenic in humans molds- multicellular, cottony colonies; composed of long, threadlike chains of cells called hyphae yeasts- unicellular, usually egg shaped in medically important fungi, most attack superficial tissues ringworm-- extremely uncommon after puberty athlete's foot- common in moist, warm, dark places like sweaty feet Jock itch- actually more common in females. can spread into vagina Candida albicans- multiple diseases, including thrush (mouth and throat), dermatitis (skin disease), "yeast infection". Is common inhabitant of human gut. Some attack deeper tissues: Histoplasmosis carried by starlings Coccidiomycosis ("valley fever") Blastomycosis (blood and internal organs) Many are beneficial: Saccharomyces cerevisiae: bread, brewing, wine making (this was the first domesticated microorganism) Penicillium chrysogenum, Penicillium notatum-- source of penicillin Penicillium roquefortii-- gives blue cheese its flavor Protozoans these are protists most are motile can cause malaria, amebic dysentery, African sleeping sickness, schistosomaisis Algae these are also protists they contain chlorophyll and photosynthesize may be unicellular, or multicellular, but the cells are not differentiated into tissues primary source of atmospheric oxygen

may indicate pollution and cause eutrophication of lakes basis of aquatic food webs Groups of prokaryotes Eubacteria: Typical bacteria appendaged or budding bacteria actinomycetes sheathed bacteria mycoplasmas gliding bacteria myxobacteria spirochetes Rickettsia Chlamydia Cyanobacteria Archaea: extreme thermophiles halophiles methanogens


				
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