Transcript Chapter 26
CHAPTER 26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Origins of Life • Cell is the basic unit of life • Today all cells come from pre-existing cells • The Earth formed as a hot mass of molten rock about 4.5 billion years ago (BYA) – As it cooled, chemically-rich oceans were formed from water condensation • Life arose spontaneously – Ocean’s edge, hydrothermal deep-sea vents, or elsewhere 2 Fundamental Properties of Life • • • • • • • • Cellular organization Sensitivity Growth Development Reproduction Regulation Homeostasis Heredity 3 • Panspermia – Earth may have been “infected” with life from some other planet – Meteor or cosmic dust may have carried complex organic molecules to earth – Kicked off evolution of life • Frozen water found on Mars 4 Conditions on Early Earth • Seems likely that Earth’s first organisms emerged and lived at very high temperatures • First organisms emerged between 3.8 and 2.5 BYA • Early atmosphere composition not agreed on – May have been a reducing atmosphere – Would have made it easier to form carbon-rich molecules 5 • In 1953, Miller and Urey did an experiment that reproduced early atmosphere – Assembled reducing atmosphere rich in hydrogen with no oxygen gas – Atmosphere placed over liquid water – Temperature below 100ºC – Simulate lightning with sparks 6 7 • Found within a week that methane gas (CH4) converted into other simple carbon compounds – Compounds combined to form simple molecules and then more complex molecules • Later experiments produced more than 30 carbon compounds including amino acids – Adenine also produced 8 • RNA may have been first genetic material • Amino acids polymerized into proteins • Metabolic pathways emerged – Primitive organisms may have been autotrophic – built what they needed • Lipid bubbles could increase the probability of metabolic reactions – Leads to cell membranes 9 Classification of Organisms • More than 2000 years ago, Aristotle divided living things into animals and plants • Later, basic units were called genera – Felis (cats) and Equus (horses) • In the 1750s, Carolus Linnaeus instituted the use of two-part names, or binomials – Apis mellifera the European honeybee – Genus name capitalized, all in italics 10 • Taxonomy is the science of classifying living things – A classification level is called a taxon • Scientific names avoid the confusion caused by common names 11 • 6-kingdom system – 4 eukaryotic kingdoms • • • • Plantae Each fundamentally different Fungi Animalia Protista – did not fit into 3 other kingdoms – 2 prokaryotic kingdoms • Archaea • Bacteria 12 Copyright © The McGraw-Hill Companies, Inc. 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Domain Bacteria (Bacteria) Domain Archaea (Archaebacteria) Domain Eukarya (Eukaryotes) Common Ancestor a. • 3 domain system – Domain Archaea – Domain Bacteria – Domain Eukarya 13 Bacteria • Most abundant organisms on Earth • Key roles in biosphere – Extract nitrogen from the air, and recycle carbon and sulfur – Perform much of the world’s photosynthesis • Responsible for many forms of disease • Highly diverse 14 Archaea • Shared characteristics – Cell walls lack peptidoglycan (found in bacteria) – Membrane lipids are different from all other organisms • Divided into three general categories – Methanogens – Extremophiles – Nonextreme archaea 15 • Methanogens – Use H2 to reduce CO2 to CH4 – Strict anaerobes that live in swamps and guts • Extremophiles – Thermophiles – High temperatures (60–80ºC) – Halophiles – High salt – Acidophiles – Low pH (pH = 0.7) • Nonextreme archaea – Grow in same environments as bacteria – Nanoarchaeum equitens – Smallest cellular genome 16 Eukarya • Prokaryotes ruled the earth for at least one billion years • Eukaryotes appeared about 2.5 BYA • Their structure and function allowed multicellular life to evolve • Eukaryotes have a complex cell organization – Extensive endomembrane system divides the cell into functional compartments 17 • Mitochondria and chloroplasts most likely gained entry by endosymbiosis • Mitochondria were derived from purple nonsulfur bacteria • Chloroplasts from cyanobacteria 18 Key Eukaryotic Characteristics • Compartmentalization – Allows for increased subcellular specialization – Nuclear membrane allows for additional levels of control of transcription and translation • Multicellularity – Allows for differentiation of cells into tissues • Sexual reproduction – Allows for greater genetic diversity 19 Viruses • Are literally “parasitic” chemicals – DNA or RNA wrapped in protein • Cannot reproduce on their own • Not considered alive – cannot be placed in a kingdom 20 Copyright © The McGraw-Hill Companies, Inc. 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Vaccinia virus (cowpox) Herpes simplex virus Rhinovirus (common cold) Influenza virus T4 bacteriophage HIV-1 (AIDS) Tobacco mosaic virus (TMV) Adenovirus (respiratory virus) Poliovirus (polio) 100 nm Ebola virus 21 Making Sense of the Protists • Represents tension between traditional classification and use of evolutionary relationships • Eukaryotes diverged rapidly as atmosphere shift from anaerobic to aerobic – May never be able to sort out relationships during this time • Protist is a catchall for eukaryotes that are not plant, fungus, or animal 22 • Land plants arose from an ancestral green alga only once during evolution 23 Sorting Out the Animals • Origins of segmentation – Used in the past to group arthropods and annelids close together – rRNA sequences now suggest that these two groups are distantly related – Segmentation likely evolved independently in these two groups, as well as in chordates 24 • Division based on embryonic development – Protostomes develop the mouth before the anus in embryonic development • Annelids and arthropods among others – Deuterostomes develop the anus first • Chordates including humans • Protostomes divided further into – Lophotrochozoans • Flatworms, mollusks, and annelids – Ecdysozoans • Roundworms and arthropods 25 • Segmentation is regulated by the Hox gene family – Hox ancestral genes already present in ancestor to all groups – Members were co-opted at least three times 26 Within the arthropods, insects have traditionally been separated from the crustaceans – Uniramous vs. biramous appendages However, molecular data is questioning this classification – Distal-less, a Hox gene, initiates development of both types of appendages 27 The Mammalian Family Tree • Over 90% of mammals are eutherians or placental mammals – Now divided into four major groups • First major split occurred 100 MYA when Africa split from South America 28