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Life is carbon based. Each carbon atom can bind to another one producing acarbon skeletonthat can be straight, branched, or ring shaped. | https://openstax.org/books/microbiology/pages/7-summary |
The same numbers and types of atoms may bond together in different ways to yield different molecules calledisomers. Isomers may differ in the bonding sequence of their atoms (structural isomers) or in the spatial arrangement of atoms whose bonding sequences are the same (stereoisomers), and their physical and chemical ... | https://openstax.org/books/microbiology/pages/7-summary |
Functional groupsconfer specific chemical properties to molecules bearing them. Common functional groups in biomolecules are hydroxyl, methyl, carbonyl, carboxyl, amino, phosphate, and sulfhydryl. | https://openstax.org/books/microbiology/pages/7-summary |
Macromoleculesarepolymersassembled from individual units, themonomers, which bind together like building blocks. Many biologically significant macromolecules are formed bydehydration synthesis, a process in which monomers bind together by combining their functional groups and generating water molecules as byproducts. | https://openstax.org/books/microbiology/pages/7-summary |
Carbohydrates, the most abundant biomolecules on earth, are widely used by organisms for structural and energy-storage purposes. | https://openstax.org/books/microbiology/pages/7-summary |
Carbohydrates include individual sugar molecules (monosaccharides) as well as two or more molecules chemically linked byglycosidic bonds.Monosaccharidesare classified based on the number of carbons the molecule as trioses (3 C), tetroses (4 C), pentoses (5 C), and hexoses (6 C). They are the building blocks for the syn... | https://openstax.org/books/microbiology/pages/7-summary |
Disaccharidessuch as sucrose, lactose, and maltose are molecules composed of two monosaccharides linked together by a glycosidic bond. | https://openstax.org/books/microbiology/pages/7-summary |
Polysaccharides, orglycans, are polymers composed of hundreds of monosaccharide monomers linked together by glycosidic bonds. The energy-storage polymersstarchandglycogenare examples of polysaccharides and are all composed of branched chains of glucose molecules. | https://openstax.org/books/microbiology/pages/7-summary |
The polysaccharidecelluloseis a common structural component of the cell walls of organisms. Other structural polysaccharides, such as N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM), incorporate modified glucose molecules and are used in the construction of peptidoglycan or chitin. | https://openstax.org/books/microbiology/pages/7-summary |
Lipidsare composed mainly of carbon and hydrogen, but they can also contain oxygen, nitrogen, sulfur, and phosphorous. They provide nutrients for organisms, store carbon and energy, play structural roles in membranes, and function as hormones, pharmaceuticals, fragrances, and pigments. | https://openstax.org/books/microbiology/pages/7-summary |
Fatty acids are long-chain hydrocarbons with a carboxylic acid functional group. Their relatively long nonpolar hydrocarbon chains make themhydrophobic. Fatty acids with no double bonds aresaturated; those with double bonds areunsaturated. | https://openstax.org/books/microbiology/pages/7-summary |
Fatty acids chemically bond to glycerol to form structurally essential lipids such astriglyceridesandphospholipids.Triglycerides comprise three fatty acids bonded to glycerol, yielding a hydrophobic molecule. Phospholipids contain both hydrophobic hydrocarbon chains and polar head groups, making themamphipathicand capa... | https://openstax.org/books/microbiology/pages/7-summary |
Biological membranes are large-scale structures based on phospholipid bilayers that provide hydrophilic exterior and interior surfaces suitable for aqueous environments, separated by an intervening hydrophobic layer. These bilayers are the structural basis for cell membranes in most organisms, as well as subcellular co... | https://openstax.org/books/microbiology/pages/7-summary |
Isoprenoidsare lipids derived from isoprene molecules that have many physiological roles and a variety of commercial applications. | https://openstax.org/books/microbiology/pages/7-summary |
A wax is a long-chain isoprenoid that is typically water resistant; an example of a wax-containing substance is sebum, produced by sebaceous glands in the skin.Steroidsare lipids with complex, ringed structures that function as structural components of cell membranes and as hormones.Sterolsare a subclass of steroids co... | https://openstax.org/books/microbiology/pages/7-summary |
Bacteria produce hopanoids, structurally similar to cholesterol, to strengthen bacterial membranes. Fungi and protozoa produce a strengthening agent called ergosterol. | https://openstax.org/books/microbiology/pages/7-summary |
Amino acids are small molecules essential to all life. Each has an α carbon to which a hydrogen atom, carboxyl group, and amine group are bonded. The fourth bonded group, represented byR,varies in chemical composition, size, polarity, and charge among different amino acids, providing variation in properties. | https://openstax.org/books/microbiology/pages/7-summary |
Peptidesare polymers formed by the linkage of amino acids via dehydration synthesis. The bonds between the linked amino acids are calledpeptide bonds.The number of amino acids linked together may vary from a few to many. | https://openstax.org/books/microbiology/pages/7-summary |
Proteinsare polymers formed by the linkage of a very large number of amino acids. They perform many important functions in a cell, serving as nutrients and enzymes; storage molecules for carbon, nitrogen, and energy; and structural components. | https://openstax.org/books/microbiology/pages/7-summary |
The structure of a protein is a critical determinant of its function and is described by a graduated classification:primary,secondary,tertiary, andquaternary. Thenative structureof a protein may be disrupted bydenaturation, resulting in loss of its higher-order structure and its biological function. | https://openstax.org/books/microbiology/pages/7-summary |
Some proteins are formed by several separate protein subunits, the interaction of these subunits composing thequaternary structureof the protein complex. | https://openstax.org/books/microbiology/pages/7-summary |
Conjugated proteinshave a nonpolypeptide portion that can be a carbohydrate (forming aglycoprotein) or a lipid fraction (forming alipoprotein). These proteins are important components of membranes. | https://openstax.org/books/microbiology/pages/7-summary |
Accurate identification of bacteria is essential in a clinical laboratory for diagnostic and management of epidemics, pandemics, and food poisoning caused by bacterial outbreaks. | https://openstax.org/books/microbiology/pages/7-summary |
The phenotypic identification of microorganisms involves using observable traits, including profiles of structural components such as lipids, biosynthetic products such as sugars or amino acids, or storage compounds such as poly-β-hydroxybutyrate. | https://openstax.org/books/microbiology/pages/7-summary |
An unknown microbe may be identified from the unique mass spectrum produced when it is analyzed bymatrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF). | https://openstax.org/books/microbiology/pages/7-summary |
Microbes can be identified by determining their lipid compositions, usingfatty acid methyl esters(FAME) orphospholipid-derived fatty acids(PLFA)analysis. | https://openstax.org/books/microbiology/pages/7-summary |
Proteomic analysis, the study of all accumulated proteins of an organism; can also be used for bacterial identification. | https://openstax.org/books/microbiology/pages/7-summary |
Glycoproteins in the plasma membrane or cell wall structures can bind to lectins or antibodies and can be used for identification. | https://openstax.org/books/microbiology/pages/7-summary |
Metabolismincludes chemical reactions that break down complex molecules (catabolism) and those that build complex molecules (anabolism). | https://openstax.org/books/microbiology/pages/8-summary |
Organisms may be classified according to their source of carbon.Autotrophsconvert inorganic carbon dioxide into organic carbon;heterotrophsuse fixed organic carbon compounds. | https://openstax.org/books/microbiology/pages/8-summary |
Organisms may also be classified according to their energy source.Phototrophsobtain their energy from light.Chemotrophsget their energy from chemical compounds.Organotrophsuse organic molecules, andlithotrophsuse inorganic chemicals. | https://openstax.org/books/microbiology/pages/8-summary |
Cellularelectron carriersaccept high-energy electrons from foods and later serve as electron donors in subsequentredox reactions.FAD/FADH2, NAD+/NADH,and NADP+/NADPHare important electron carriers. | https://openstax.org/books/microbiology/pages/8-summary |
Adenosine triphosphate (ATP)serves as the energy currency of the cell, safely storing chemical energy in its twohigh-energy phosphate bondsfor later use to drive processes requiring energy. | https://openstax.org/books/microbiology/pages/8-summary |
Enzymesare biologicalcatalyststhat increase the rate of chemical reactions inside cells by lowering the activation energy required for the reaction to proceed. | https://openstax.org/books/microbiology/pages/8-summary |
In nature,exergonic reactionsdo not require energy beyond activation energy to proceed, and they release energy. They may proceed without enzymes, but at a slow rate. Conversely,endergonic reactionsrequire energy beyond activation energy to occur. In cells, endergonic reactions are coupled to exergonic reactions, makin... | https://openstax.org/books/microbiology/pages/8-summary |
Substratesbind to the enzymeâsactive site. This process typically alters the structures of both the active site and the substrate, favoring transition-state formation; this is known asinduced fit. | https://openstax.org/books/microbiology/pages/8-summary |
Cofactorsare inorganic ions that stabilize enzyme conformation and function.Coenzymesare organic molecules required for proper enzyme function and are often derived from vitamins. An enzyme lacking a cofactor or coenzyme is anapoenzyme;an enzyme with a bound cofactor or coenzyme is aholoenzyme. | https://openstax.org/books/microbiology/pages/8-summary |
Competitive inhibitorsregulate enzymes by binding to an enzymeâs active site, preventing substrate binding.Noncompetitive (allosteric) inhibitorsbind toallosteric sites, inducing a conformational change in the enzyme that prevents it from functioning.Feedback inhibitionoccurs when the product of a metabolic pathway n... | https://openstax.org/books/microbiology/pages/8-summary |
Glycolysisis the first step in the breakdown of glucose, resulting in the formation of ATP, which is produced bysubstrate-level phosphorylation; NADH; and two pyruvate molecules. Glycolysis does not use oxygen and is not oxygen dependent. | https://openstax.org/books/microbiology/pages/8-summary |
After glycolysis, a three-carbon pyruvate is decarboxylated to form a two-carbon acetyl group, coupled with the formation of NADH. The acetyl group is attached to a large carrier compound called coenzyme A. | https://openstax.org/books/microbiology/pages/8-summary |
After the transition step, coenzyme A transports the two-carbon acetyl to theKrebs cycle, where the two carbons enter the cycle. Per turn of the cycle, one acetyl group derived from glycolysis is further oxidized, producing three NADH molecules, one FADH2, and one ATP bysubstrate-level phosphorylation, and releasing tw... | https://openstax.org/books/microbiology/pages/8-summary |
The Krebs cycle may be used for other purposes. Many of the intermediates are used to synthesize important cellular molecules, including amino acids, chlorophylls, fatty acids, and nucleotides. | https://openstax.org/books/microbiology/pages/8-summary |
Most ATP generated during the cellular respiration of glucose is made byoxidative phosphorylation. | https://openstax.org/books/microbiology/pages/8-summary |
Anelectron transport system (ETS)is composed of a series of membrane-associated protein complexes and associated mobile accessory electron carriers. The ETS is embedded in the cytoplasmic membrane of prokaryotes and the inner mitochondrial membrane of eukaryotes. | https://openstax.org/books/microbiology/pages/8-summary |
Each ETS complex has a different redox potential, and electrons move from electron carriers with more negative redox potential to those with more positive redox potential. | https://openstax.org/books/microbiology/pages/8-summary |
To carry outaerobic respiration, a cell requires oxygen as the final electron acceptor. A cell also needs a complete Krebs cycle, an appropriate cytochrome oxidase, and oxygen detoxification enzymes to prevent the harmful effects of oxygen radicals produced during aerobic respiration. | https://openstax.org/books/microbiology/pages/8-summary |
Organisms performinganaerobic respirationuse alternative electron transport system carriers for the ultimate transfer of electrons to the final non-oxygen electron acceptors. | https://openstax.org/books/microbiology/pages/8-summary |
Microbes show great variation in the composition of their electron transport systems, which can be used for diagnostic purposes to help identify certain pathogens. | https://openstax.org/books/microbiology/pages/8-summary |
As electrons are passed from NADH and FADH2through an ETS, the electron loses energy. This energy is stored through the pumping of H+across the membrane, generating aproton motive force. | https://openstax.org/books/microbiology/pages/8-summary |
The energy of this proton motive force can be harnessed by allowing hydrogen ions to diffuse back through the membrane bychemiosmosisusingATP synthase. As hydrogen ions diffuse through down their electrochemical gradient, components of ATP synthase spin, making ATP from ADP and Piby oxidative phosphorylation. | https://openstax.org/books/microbiology/pages/8-summary |
Aerobic respiration forms more ATP (a maximum of 34 ATP molecules) during oxidative phosphorylation than does anaerobic respiration (between one and 32 ATP molecules). | https://openstax.org/books/microbiology/pages/8-summary |
Fermentation uses an organic molecule as a final electron acceptor to regenerate NAD+from NADH so that glycolysis can continue. | https://openstax.org/books/microbiology/pages/8-summary |
Fermentation does not involve an electron transport system, and no ATP is made by the fermentation process directly. Fermenters make very little ATPâonly two ATP molecules per glucose molecule during glycolysis. | https://openstax.org/books/microbiology/pages/8-summary |
Microbial fermentation processes have been used for the production of foods and pharmaceuticals, and for the identification of microbes. | https://openstax.org/books/microbiology/pages/8-summary |
During lactic acid fermentation, pyruvate accepts electrons from NADH and is reduced to lactic acid. Microbes performinghomolactic fermentationproduce only lactic acid as the fermentation product; microbes performingheterolactic fermentationproduce a mixture of lactic acid, ethanol and/or acetic acid, and CO2. | https://openstax.org/books/microbiology/pages/8-summary |
Lactic acid production by the normal microbiota prevents growth of pathogens in certain body regions and is important for the health of the gastrointestinal tract. | https://openstax.org/books/microbiology/pages/8-summary |
During ethanol fermentation, pyruvate is first decarboxylated (releasing CO2) to acetaldehyde, which then accepts electrons from NADH, reducing acetaldehyde to ethanol. Ethanol fermentation is used for the production of alcoholic beverages, for making bread products rise, and for biofuel production. | https://openstax.org/books/microbiology/pages/8-summary |
Fermentation products of pathways (e.g., propionic acid fermentation) provide distinctive flavors to food products. Fermentation is used to produce chemical solvents (acetone-butanol-ethanol fermentation) and pharmaceuticals (mixed acid fermentation). | https://openstax.org/books/microbiology/pages/8-summary |
Specific types of microbes may be distinguished by their fermentation pathways and products. Microbes may also be differentiated according to the substrates they are able to ferment. | https://openstax.org/books/microbiology/pages/8-summary |
Collectively, microbes have the ability to degrade a wide variety of carbon sources besides carbohydrates, including lipids and proteins. The catabolic pathways for all of these molecules eventually connect into glycolysis and the Krebs cycle. | https://openstax.org/books/microbiology/pages/8-summary |
Several types of lipids can be microbially degraded. Triglycerides are degraded by extracellularlipases, releasing fatty acids from the glycerol backbone. Phospholipids are degraded byphospholipases, releasing fatty acids and the phosphorylated head group from the glycerol backbone. Lipases and phospholipases act as vi... | https://openstax.org/books/microbiology/pages/8-summary |
Fatty acids can be further degraded inside the cell throughβ-oxidation, which sequentially removes two-carbon acetyl groups from the ends of fatty acid chains. | https://openstax.org/books/microbiology/pages/8-summary |
Protein degradation involves extracellularproteasesthat degrade large proteins into smaller peptides. Detection of the extracellular proteases gelatinase and caseinase can be used to differentiate clinically relevant bacteria. | https://openstax.org/books/microbiology/pages/8-summary |
Heterotrophs depend on the carbohydrates produced by autotrophs, many of which are photosynthetic, converting solar energy into chemical energy. | https://openstax.org/books/microbiology/pages/8-summary |
Different photosynthetic organisms use different mixtures ofphotosynthetic pigments, which increase the range of the wavelengths of light an organism can absorb. | https://openstax.org/books/microbiology/pages/8-summary |
Photosystems(PSI and PSII) each contain alight-harvesting complex, composed of multiple proteins and associated pigments that absorb light energy. Thelight-dependent reactionsof photosynthesis convert solar energy into chemical energy, producing ATP and NADPH or NADH to temporarily store this energy. | https://openstax.org/books/microbiology/pages/8-summary |
Inoxygenic photosynthesis, H2O serves as the electron donor to replace the reaction center electron, and oxygen is formed as a byproduct. Inanoxygenic photosynthesis, other reduced molecules like H2S or thiosulfate may be used as the electron donor; as such, oxygen is not formed as a byproduct. | https://openstax.org/books/microbiology/pages/8-summary |
Noncyclic photophosphorylationis used in oxygenic photosynthesis when there is a need for both ATP and NADPH production. If a cellâs needs for ATP outweigh its needs for NADPH, then it may carry outcyclic photophosphorylationinstead, producing only ATP. | https://openstax.org/books/microbiology/pages/8-summary |
Thelight-independent reactionsof photosynthesis use the ATP and NADPH from the light-dependent reactions to fix CO2into organic sugar molecules. | https://openstax.org/books/microbiology/pages/8-summary |
The recycling of inorganic matter between living organisms and their nonliving environment is called abiogeochemical cycle. Microbes play significant roles in these cycles. | https://openstax.org/books/microbiology/pages/8-summary |
In thecarbon cycle, heterotrophs degrade reduced organic molecule to produce carbon dioxide, whereas autotrophs fix carbon dioxide to produce organics.Methanogenstypically form methane by using CO2as a final electron acceptor during anaerobic respiration; methanotrophs oxidize the methane, using it as their carbon sour... | https://openstax.org/books/microbiology/pages/8-summary |
In thenitrogen cycle, nitrogen-fixing bacteria convert atmospheric nitrogen into ammonia (ammonification). The ammonia can then be oxidized to nitrite and nitrate (nitrification). Nitrates can then be assimilated by plants. Soil bacteria convert nitrate back to nitrogen gas (denitrification). | https://openstax.org/books/microbiology/pages/8-summary |
Insulfur cycling, many anoxygenic photosynthesizers and chemoautotrophs use hydrogen sulfide as an electron donor, producing elemental sulfur and then sulfate; sulfate-reducing bacteria and archaea then use sulfate as a final electron acceptor in anaerobic respiration, converting it back to hydrogen sulfide. | https://openstax.org/books/microbiology/pages/8-summary |
Human activities that introduce excessive amounts of naturally limited nutrients (like iron, nitrogen, or phosphorus) to aquatic systems may lead to eutrophication. | https://openstax.org/books/microbiology/pages/8-summary |
Microbialbioremediationis the use of microbial metabolism to remove or degradexenobioticsand other environmental contaminants and pollutants. Enhanced bioremediation techniques may involve the introduction of non-native microbes specifically chosen or engineered for their ability to degrade contaminants. | https://openstax.org/books/microbiology/pages/8-summary |
Most bacterial cells divide bybinary fission.Generation timein bacterial growth is defined as thedoubling timeof the population. | https://openstax.org/books/microbiology/pages/9-summary |
Cells in a closed system follow a pattern of growth with four phases:lag,logarithmic (exponential),stationary, anddeath. | https://openstax.org/books/microbiology/pages/9-summary |
Cells can be counted bydirect viable cell count. Thepour plateandspread platemethods are used to plateserial dilutionsinto or onto, respectively, agar to allow counting of viable cells that give rise tocolony-forming units.Membrane filtrationis used to count live cells in dilute solutions. Themost probable cell number ... | https://openstax.org/books/microbiology/pages/9-summary |
Indirect methods can be used to estimateculture densityby measuringturbidityof a culture or live cell density by measuring metabolic activity. | https://openstax.org/books/microbiology/pages/9-summary |
Other patterns of cell division include multiple nucleoid formation in cells; asymmetric division, as inbudding; and the formation of hyphae and terminal spores. | https://openstax.org/books/microbiology/pages/9-summary |
Biofilmsare communities of microorganisms enmeshed in a matrix ofextracellular polymeric substance. The formation of a biofilm occurs whenplanktoniccells attach to a substrate and becomesessile. Cells in biofilms coordinate their activity by communicating throughquorum sensing. | https://openstax.org/books/microbiology/pages/9-summary |
Biofilms are commonly found on surfaces in nature and in the human body, where they may be beneficial or cause severe infections. Pathogens associated with biofilms are often more resistant to antibiotics and disinfectants. | https://openstax.org/books/microbiology/pages/9-summary |
Aerobic and anaerobic environments can be found in diverse niches throughout nature, including different sites within and on the human body. | https://openstax.org/books/microbiology/pages/9-summary |
Microorganisms vary in their requirements for molecular oxygen.Obligate aerobesdepend on aerobic respiration and use oxygen as a terminal electron acceptor. They cannot grow without oxygen. | https://openstax.org/books/microbiology/pages/9-summary |
Obligate anaerobescannot grow in the presence of oxygen. They depend on fermentation and anaerobic respiration using a final electron acceptor other than oxygen. | https://openstax.org/books/microbiology/pages/9-summary |
Facultative anaerobesshow better growth in the presence of oxygen but will also grow without it. | https://openstax.org/books/microbiology/pages/9-summary |
Althoughaerotolerant anaerobesdo not perform aerobic respiration, they can grow in the presence of oxygen. Most aerotolerant anaerobes test negative for the enzymecatalase. | https://openstax.org/books/microbiology/pages/9-summary |
Microaerophilesneed oxygen to grow, albeit at a lower concentration than 21% oxygen in air. | https://openstax.org/books/microbiology/pages/9-summary |
Optimum oxygen concentrationfor an organism is the oxygen level that promotes the fastest growth rate. Theminimum permissive oxygen concentrationand themaximum permissive oxygen concentrationare, respectively, the lowest and the highest oxygen levels that the organism will tolerate. | https://openstax.org/books/microbiology/pages/9-summary |
Peroxidase,superoxide dismutase, andcatalaseare the main enzymes involved in the detoxification of thereactive oxygen species. Superoxide dismutase is usually present in a cell that can tolerate oxygen. All three enzymes are usually detectable in cells that perform aerobic respiration and produce more ROS. | https://openstax.org/books/microbiology/pages/9-summary |
Acapnophileis an organism that requires a higher than atmospheric concentration of CO2to grow. | https://openstax.org/books/microbiology/pages/9-summary |
Bacteria are generallyneutrophiles. They grow best at neutral pH close to 7.0. | https://openstax.org/books/microbiology/pages/9-summary |
Acidophilesgrow optimally at a pH near 3.0.Alkaliphilesare organisms that grow optimally between a pH of 8 and 10.5. Extreme acidophiles and alkaliphiles grow slowly or not at all near neutral pH. | https://openstax.org/books/microbiology/pages/9-summary |
Microorganisms grow best at theiroptimum growth pH. Growth occurs slowly or not at all below theminimum growth pHand above themaximum growth pH. | https://openstax.org/books/microbiology/pages/9-summary |
Microorganisms thrive at a wide range of temperatures; they have colonized different natural environments and have adapted to extreme temperatures. Both extreme cold and hot temperatures require evolutionary adjustments to macromolecules and biological processes. | https://openstax.org/books/microbiology/pages/9-summary |
Psychrophilesgrow best in the temperature range of 0â15 °C whereaspsychrotrophsthrive between 4°C and 25 °C. | https://openstax.org/books/microbiology/pages/9-summary |
Mesophilesgrow best at moderate temperatures in the range of 20 °C to about 45 °C. Pathogens are usually mesophiles. | https://openstax.org/books/microbiology/pages/9-summary |
Thermophilesandhyperthemophilesare adapted to life at temperatures above 50 °C. | https://openstax.org/books/microbiology/pages/9-summary |
Adaptations to cold and hot temperatures require changes in the composition of membrane lipids and proteins. | https://openstax.org/books/microbiology/pages/9-summary |
Halophilesrequire high salt concentration in the medium, whereashalotolerantorganisms can grow and multiply in the presence of high salt but do not require it for growth. | https://openstax.org/books/microbiology/pages/9-summary |
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