Phylogeny: The Study of Evolutionary Relationships of Living Organisms u Over 1.5 million differentorganisms have been identified to date. Chapter 10: Classification of u Many similarities among living organisms: Microorganisms u Made up of cells surrounded by a plasma membrane. u Use ATP as energy source. u Store genetic information as DNA. u Ribosomes are the site of protein synthesis. u Both differences and similarities among organisms are caused by natural selection (Darwin, 1858). u Organisms can be classified into taxonomic categories (taxa), based on the differences and similarities among them.
Phylogeny: The Study of Evolutionary Phylogeny: The Study of Evolutionary Relationships of Living Organisms Relationships of Living Organisms u Ancient Greeks classified all living organisms u In 1930s electron microscopy made it clear that into two groups bacterial cells lacked a nucleus. The term u Kingdom Plantae procaryote was introduced in 1937. u Kingdom Animalia u In 1959 Kingdom Fungi was established. u In 1850s bacteria and fungi were incorrectly placed in the Plant Kingdom. u In 1961 the current definition of the term procaryote was established. u In 1860s Kingdom Protista was proposed to include bacteria, fungi, algae, and protozoa, but u In 1968 the Kingdom Procaryotae was accepted many scientists still classified bacteria and fungi by biologists. as plants. u In 1969 Robert Whitaker proposed a five- Intense disagreement over classification of kingdom system of biological classification for bacteria and fungi persisted over 100 years. all living organisms.
Five-Kingdom System of Biological Classification Five-Kingdom Classification System Proposed in 1969 by Robert Whitaker : 1.Kingdom Procaryotae (Monera): Oldest known cells. Lived over 3.5 billion years ago. Lack a nucleus and membrane bound organelles. The other four kingdoms are eucaryotes. Have a true nucleus and membrane bound organelles. 2. Kingdom Protista: Mostly unicellular, lack tissue organization. Most have flagella during life. 3. Kingdom Fungi: May be unicellular (yeasts) or multicellular (molds). Many are saprotrophs. 4. Kingdom Plantae: Multicellular, photosynthetic. 5. Kingdom Animalia: Multicellular, heterotrophs that ingest food through a mouth or oral cavity.
1 Differences Between Eucaryotic and Procaryotes: Lack Nucleus and Procaryotic Cells Membrane-Bound Organelles Procaryotes Eucaryotes Cell size 0.2-2 um in diameter 10-100 um in diameter Nucleus Absent Present Membranous Organelles Absent Present Cell Wall Chemically complex When present, simple Ribosomes Smaller (70S) Larger (80S) in cell 70S in organelles DNA Single circular Multiple linear chromosome chromosomes (histones) Cell Division Binary fission Mitosis
Phylogeny Phylogeny: The Three Domain System The Three Domain System Domain: In 1978 Carl Woese proposed this level of Recent developments in molecular biology and classification above kingdom. biochemistry have revealed that there are two There are three domains based on the following types of procaryotic cells, based on differences in distinguishing criteria: their ribosomes, cell walls, and metabolism. u Cell wall composition 1. Eubacteria: “True bacteria”. u Membrane lipids u Cell wall contains peptidoglycan. u RNA sequence u Sensitive to antibiotics. u Protein synthesis 2. Archaeabacteria:“Ancient bacteria” u Antibiotic sensitivity u Cell walls lack peptidoglycan, resistant to antibiotics. u Live in extreme environments I. Domain Eubacteria: “True bacteria”. u Three kingdoms: II. Domain Archaeabacteria:“Ancient bacteria” 1. Methanogens: Strict anaerobes that produce methane. III. Domain Eucarya: All eucaryotes: Protista, 2. Extreme Halophiles: Require high salt concentrations. Fungi, Plantae , and Animalia. 3. Thermoacidophiles: Live in hot, acidic environments.
2 Classification of Organisms Phylogenetic Relationships of Procaryotes Scientific Nomenclature u Scientific nomenclature: Universal system for naming and classifying living organisms. Initially developed in the 18th century by Carl Linnaeus. u Binomial nomenclature: Each organism (species) has a two part name. Names are either italicized or underlined. u Genus name: Always capitalized, always a noun. May use initial. u speciesname: Always lower case, usually an adjective. u Names are usually derived from Latin (or Greek) or may have latinized endings. Examples: u Homo sapiens (H. sapiens): Human u Penicillium notatum (P. notatum): Mold that produces penicillin u Canis familiaris (C. familiaris): Domestic dog
Classification of Organisms Taxonomic Categories Hierarchy of Taxonomic Categories
DOMAIN Division (Bacteria) Kingdom u Phylum or Division (Bacteria) u Class u Order u Family u Genus species
Classification of Bacteria Scientific Nomenclature Classification of Viruses u Bacterial species: Population of cells with similar u Viruses are not considered living organisms by most characteristics. biologists, because they lack cells and their own anabolic u Bacterial strain: A subgroup of a bacterial species that machinery. has distinguishing characteristics. Identified by numbers, u Obligate intracellular parasites. Must have evolved after letters, or names that follow the scientific name. their host cell evolved. u Escherichia coli O157:H7: Strain that causes bloody diarrhea. u Viral species: Population of viruses with similar u Bergey’s Manual: Provides a reference for identifying characteristics that occupies a particular ecological niche. and classifying bacteria. u Morphology u Classification initially based on cell morphology, staining, u Genes metabolism, biochemistry, serology, etc. u Enzymes u More recently, DNA, RNA, and protein sequence analysis are being used to study evolutionary relationships.
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