Appendixes



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The Limits of Organic Life in Planetary Systems Appendixes

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The Limits of Organic Life in Planetary Systems A Glossary Abiotic Of or relating to nonliving things; independent of life or living organisms Acidophile An organism adapted to living in highly acidic environments ADP Adenosine diphosphate Aerosol A fine aerial suspension of liquid (mist, fog) or solid (dust, fume, smoke) particles Albedo The fraction of light that is reflected by a surface; commonly used in astronomy to describe the reflective properties of planets, satellites, and asteroids Alkalophile An organism that is adapted to living in highly alkaline environments Amino acid Any organic compound containing an amino (NH2) and a carboxyl (COOH) group; there are 20 α-amino acids from which proteins are synthesized during ribosomal translation of mRNA Anaerobe An organism that lives and reproduces in the absence of dissolved oxygen, instead using oxidants such as iron and sulfur compounds in energy metabolism Anoxic Lacking oxygen Aquaporin A water channel that form pores in the membranes of cells and selectively conducts water molecules through the membrane, while preventing the passage of ions (such as sodium and potassium) and other small molecules Archaea (Archaebacteria) A group of unique microorganisms classified as bacteria that are related only distantly to eukaryotes and other prokaryotes Aromatic hydrocarbon A member of the class of hydrocarbons consisting of assemblages of cyclic conjugated carbon atoms and characterized by large resonance energies Asteroid A small, rocky body in orbit around the Sun, found mainly between the orbits of Mars and Jupiter

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The Limits of Organic Life in Planetary Systems ATP Adenosine triphosphate Autotroph An organism that can synthesize its own food—complex organic compounds—using simple inorganic sources, such as carbon dioxide Biocatalysis The process by which an enzyme expedites biochemical reactions without itself being changed Biocryosolvent A biological solvent for maintaining constant low temperature Biofilm An aggregate of microbes with a distinct architecture Biopolymer A large molecule having a repeating structural feature assembled by a living system from building blocks; proteins (built from amino acids) and DNA (built from nucleotides) are two examples Biotic Of or relating to living things; caused or produced by living organisms Bolide A detonating meteor fireball Carbohydrate A group of organic compounds that consist of carbon, hydrogen, and oxygen; carbohydrates can be simple sugars that consist of a single sugar molecule and cannot be further decomposed by hydrolysis, or complex sugars such as starch Carbonaceous chondrite A rare type of stony meteorite that is rich in carbon compounds and is thought to be relatively unaltered since the beginning of the solar system; its spectrum (and probably also its composition) closely resembles that of the C-type asteroids Carbonate mineral A mineral having the carbonate ion, such as calcite (calcium carbonate), siderite (iron carbonate), and magnesite (magnesium carbonate) Catalyst A substance that enhances the rate of reaction by providing a lower-energy alternative pathway Chemolithoautotroph An organism capable of generating metabolically useful energy by the oxidation of inorganic compounds Chirality Handedness; property of a molecule configured such that it cannot be superimposed on its mirror image Chondrite A stony meteorite that contains spherical bodies of pyroxene and olivine minerals Codon The basic unit of the genetic code; a set of any three adjacent bases in DNA or RNA Colemanite A natural white or colorless hydrated calcium borate, Ca2B6O11·5H2O Cosmic rays High-energy charged particles consisting of atomic nuclei, electrons, and protons and originating from the Sun and from energetic astrophysical processes (e.g., those associated with black holes, supernovas, and so on) Cryosolvent A solvent for maintaining constant low temperature Cryptoendolith An organism that lives within rocks on Earth’s surface Cytotoxic Producing toxic effects on cells

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The Limits of Organic Life in Planetary Systems Deamination Removal of an amine group, usually by hydrolysis Decarboxylation Removal of a carbonyl radical, especially from amino acids and proteins Deoxyribose A sugar, C5H10O4, that is a major constituent of DNA DNA Deoxyribonucleic acid; the genetic biopolymer of most terrean organisms Electrophile An electron-deficient ion or molecule that accepts a pair of electrons from its reaction partner to form a new bond Enantiomer One of an isometric pair of either crystalline forms or chemical compounds whose molecules are non-superimposable mirror images of each other; enantiomers are optically active and rotate the plane of polarized light Endergonic Requiring energy Endosymbiosis A mutually beneficial relationship between two organisms in which one lives inside the other Eubacteria The group of prokaryotes that are the true bacteria Eukaryote An organism having a membrane-bound nucleus and usually other organelles Exogenous Derived or originated externally; not arising within an organism Exopolymer A high-molecular-weight bipolymer, usually a carbohydrate, that is secreted by an organism into the environment Exopolysaccharide Polysaccharides that are secreted by an organism into the environment Extrasolar Being or originating outside the solar system Extremophile An organism adapted to living in conditions of extreme temperature, pressure, or chemical concentration Fractionation Separation of a complex mixture in successive stages into fractions, each of which is enriched in one of the components of the mixture Free radical A highly reactive chemical species carrying no charge and having a single unpaired electron in an orbital Fullerene Any of various cagelike molecules that constitute the third form of pure carbon (along with the forms diamond and graphite), whose prototype C60 (bucky-ball) is the roundest molecule that exists; fullerenes are a class of discrete molecules, soccerball-shaped forms of carbon with extraordinary stability (so named because their configuration suggests the shape of Buckminster Fuller’s famous geodesic dome) Gray (Gy) Unit of absorbed dose of ionizing radiation corresponding to the absorption of 1 J per kg of absorbing material; 1 gray = 100 rads; on Earth a typical mid-latitude, sea-level natural background level is ~0.3 mGy per year, whereas on the surface of Europa the level is almost 1010 times higher, enough to kill humans in one minute of exposure) Gyrase A type II topoisomerase that introduces negative supercoils (or relaxes positive supercoils) into DNA by looping the template so as to form a crossing, then cutting one of the double helices and passing the other through it before resealing the break, changing the linking number by two in each enzymatic step Halophilic Requiring a high salt concentration for optimal growth

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The Limits of Organic Life in Planetary Systems Heteroatom Atom other than carbon in the structure of a heterocyclic compound Heterocyclic compound Compound in which the structure contains one or more rings of atoms with at least one atom being an element other than carbon Heterotroph An organism that uses only organic matter for energy and growth Hydrophobicity The tendency to repel water Hyperthermophile An organism adapted to living in high temperatures of 80°C or higher Interstellar medium The dust, molecular clouds, and neutral hydrogen that lie between the stars of this galaxy, generally in the plane of the Milky Way, but whose density is highly variable Isomer One of two or more substances that have the same chemical composition but differ in structural form Isomerization The process whereby a compound is changed into a isomeric form Isosteres Molecules or ions of similar size and the same number of valence electrons Lipid An organic molecule that is not soluble in water and often forms membranes Liposome An artificial microscopic vesicle consisting of an aqueous core enclosed in one or more phospholipid layers Lysozome A membrane-bound organelle in the cytoplasm of most cells containing various hydrolytic enzymes that function in intracellular digestion Magnetotaxis Coordinated movement of certain motile microorganisms in response to their sensing a magnetic field Mesophilic Preferring moderate temperatures Metabolism The processes or chemical changes in a cell by which food is built up (anabolism) into living protoplasm and by which protoplasm is broken down (catabolism) into simpler compounds with the exchange of energy Metallicity A measure of the proportion of an object’s matter that is made up of chemical elements other than hydrogen and helium Methanogen An organism capable of producing methane from the decomposition of organic material Monomer A building block of a polymer, including a biopolymer; amino acids are monomers of polypeptides (proteins), and nucleotides are monomers of nucleic acids Murchison (meteorite) A carbonaceous chondrite, type II (CM2), suspected to be of cometary origin due to its high water content (12 percent) Nucleophile A molecule that contributes a pair of electrons to its reaction partner to form a new bond Nucleoside Glycosylamine made by attaching a nucleobase to a ribose or deoxyribose ring (for example, cytidine, uridine, adenosine, guanosine, thymidine, and inosine) Nucleosynthesis The process by which heavier chemical elements are synthesized from hydrogen nuclei in the interiors of stars Oligonucleotide A short polymer of 2 to 20 nucleotides

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The Limits of Organic Life in Planetary Systems Oligotroph A microorganism specifically adapted to grow under conditions of low nutrient supply Oligotrophic Term used to describe lakes or oceans that lack carbon and energy sources for photosynthetic organisms Organic Of or relating to any covalently bonded compound containing carbon atoms; derived from living systems; more recently, given the fact that all known living systems contain carbon in reduced form (i.e., not carbonate), “organic” has come to mean “containing reduced carbon” Oxaloacetate A salt or ester of oxaloacetic acid Oxidation/reduction The change in the oxidation state of atoms or ions due to the “loss” or “gain” of electrons Panspermia The theory that microorganisms or biochemical compounds from outer space are responsible for originating life on Earth and possibly in other parts of the universe where suitable atmospheric conditions exist PCR Polymerase chain reaction Peptide Any of various natural or synthetic compounds containing two or more amino acids linked by the carboxyl group of one amino acid and the amino group of another Peptidoglycan A polymer found in the cell walls of prokaryotes that consists of polysaccharide and peptide chains in a strong molecular network Peridotite Any of a group of igneous rocks composed mainly of olivine and various pyroxenes and having a granitelike texture Phosphide A compound of phosphorus and a more electropositive element or radical Phosphorylation Chemical process in which a phosphate group is added to an organic molecule Photolysis The decomposition of a substance into simpler units as a result of the action of light Phylogenetic Relating to evolutionary history Piezophile An organism adapted to living in high-pressure environments, such as hydrothermal vents Pigment A colored molecule Polycyclic aromatic hydrocarbons (PAHs) A class of very stable organic molecules that are made up of only carbon and hydrogen; are flat, with each carbon having three neighboring atoms, much like graphite; and are a standard product of combustion Polyelectrolyte An electrolyte, such as a protein or polysaccharide, that has a high molecular weight Polysaccharides A class of high-molecular-weight carbohydrates that can be broken down to monosaccharides on hydrolysis Prebiotic Occurring before life appeared on Earth Protein Any of a group of complex organic compounds, consisting essentially of com-

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The Limits of Organic Life in Planetary Systems binations of amino acids in peptide linkages, that contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur Protonated Having protons added to a base Protoplanetary disk The disk of dust and gas surrounding a star out of which planets form Psychrophilic Requiring low temperatures for growth Radiolysis The breakdown of molecules as a result of exposure to ionizing radiation Retrotransposon A transposon copied from RNA with the use of reverse transcriptase Ribosome A minute, round particle composed of RNA and protein found in the cytoplasm of living cells and active in the synthesis of proteins RNA Ribonucleic acid rRNA Ribosomal RNA Serpentinization reaction A hydrothermal reaction by which magnesium-rich silicate minerals are converted into or replaced by serpentine minerals Siderophore A molecular receptor that binds and transports iron Silane Any of a group of silicon hydrides having the general formula SiH that are analogous to the paraffin hydrocarbons Sphalerite The primary ore of zinc, occurring in usually yellow-brown or brownish-black crystals or cleavage masses, essentially ZnS with some cadmium, iron, and manganese Stereochemistry The branch of chemistry concerned with the study of how atoms or molecules are affected by their three-dimensional spatial arrangement, e.g., the study of stereoisomers Synthetic biology Engineering of biological components or systems that are not known to nature or the reengineering of existing biological components Tagish Lake (meteorite) A unique carbonaceous chondrite collected very soon after falling to Earth in a remote part of northwestern Canada in January 2001 Thermophile An organism adapted to living in high-temperature environments Thioester Compound resulting from the bonding of sulfur with an acyl group with the general formula R-S-CO-R′ Tholin A term used in planetary science to refer generally to organic heteropolymers; the reddish tar-like organic residue created in simulations of the action of ultraviolet radiation on gases typically found in planetary environments Thymidine A nucleoside, C10H14N2O5, composed of thymine and deoxyribose Vesicle A microscopic volume defined by a boundary structure; examples include self-assembled vesicles bounded by a membranous lipid bilayer, and small cavities formed in volcanic rock by entrapment of a gas bubble during solidification Vitrification The process of liquid water moving directly into the glassy state without ice crystal formation