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Acid-fast stain a procedure for assessing the ability of an organism to retain hot carbol fuchsin stain when rinsed with acidic alcohol.

Acidophilic ('acid-loving'):a term applied to organisms that show optimal growth in acid conditions (pH<5.5).

Activated sludge treatment a method of wastewater treatment involving aeration in tanks that have been seeded with a mixed microbial sludge.

Activation energy the energy required to initiate a chemical reaction.

Active site the part of an enzyme involved in binding its substrate; the site of catalytic action.

Active transport an energy-requiring process in which a substance is transported against an electrochemical gradient.

Adenosine triphosphate (ATP) the principal compound used for the storage and transfer of energy in cellular systems.

Aerobe an organism that grows in the presence of molecular oxygen, which it uses as a terminal electron acceptor in aerobic respiration.

Aerotolerant anaerobe an anaerobe that is able to tolerate the presence of oxygen, even though it does not use it.

Aetiology the cause or origin of a disease.

Aldose a sugar molecule that contains an aldehyde group.

Alga a photosynthetic, eucaryotic plant-like organism. It may be unicellular or multicellular.

Alternation of generations a pattern of sexual reproduction that includes both haploid and diploid mature individuals.

Ames test a test to assess the mutagenicity of a substance.

Amino acid an organic acid bearing both amino and carboxyl groups. The building block of proteins.

Amphipathic having a polar region at one end and a nonpolar region at the other.

Anabolism metabolic reactions involved in the synthesis of macromolecules, usually requiring an input of energy.

Anaerobe an organism that grows in the absence of molecular oxygen.

Anammox the formation of nitrogen gas by the anaerobic oxidation of ammonia and nitrite.

Angstrom unit one ten billionth (10-10) of a metre. Anisogamy the fusion of unequally sized gametes.

Anoxygenic photosynthesis a form of photosynthesis in which oxygen is not generated; found in the purple and green photosynthetic bacteria.

Antibiotic a microbially produced substance (or a synthetic derivative) that has antimicrobial properties.

Antibody a protein of high binding specificity produced by the immune systems of higher animals in response to infection by a foreign organism.

Anticodon the three-nucleotide sequence carried by a tRNA, that base-pairs with its complementary mRNA codon.

Antigenic shift a process by which major variations in viral antigens occur.

Antiseptic a chemical agent of disinfection that is mild enough to be used on human skin or tissues.

Archaea a group of prokaryotes that diverged from all others (see Bacteria) at an early stage in evolution, and that show a number of significant differences from them. One of the three domains of life.

Ascospore a haploid spore produced by members of the Ascomycota.

Ascus a sac-like structure possessed by members of the Ascomycota that contains the ascospores.

Aseptic technique a set of practical measures designed to prevent the growth of unwanted contaminants from the environment.

Assimilatory sulphate reduction the incorporation of inorganic sulphate into sulphur-containing amino acids.

Autoclave an appliance that uses steam under pressure to achieve sterilisation.

Atomic mass the average of the mass numbers of an element's different isotopes, taking into account the proportions in which they occur.

Atomic number the number of protons in the nucleus of an element.

Autotroph an organism that can derive its carbon from carbon dioxide.

Auxotroph a mutant that lacks the ability to synthesise an important nutrient such as an amino acid or vitamin, and must therefore have it provided (c.f. prototroph).

Axenic culture a pure culture containing one type of organism only, and completely free from contaminants.

Bacillus (pl. bacilli): a rod-shaped bacterium.

Bacteria procaryotes other than the Archaea (q.v.). Less formally, the term is frequently used to describe all procaryotes.

Bactericidal causing the death of bacteria.

Bacteriophage a virus whose host is a bacterial cell.

Bacteriostatic inhibiting the growth of bacteria, but not necessarily killing them.

Basidiocarp the fruiting body of members of the Basidiomycota.

Basidiospore a haploid spore produced by members of the Basidiomycota.

Basidium a club-shaped structure carrying the basidiospores in members of the Basidiomycota.

Batch culture a microbial culture grown in a closed vessel with no addition of nutrients or removal of waste products.

Benthic zone the sediment of mud and organic matter at the bottom of a pond or lake.

Beta-lactamase an enzyme that breaks a bond in the ^-lactam core of the penicillin molecule.

Bioaugmentation the deliberate introduction of specific microorganisms into an environment in order to assist in bioremediation.

Biochemical oxygen demand (BOD) the amount of oxygen needed by microorganisms to oxidise the organic content of a water sample.

Biodegradation the natural processes of breakdown of organic matter by microorganisms.

Biodeterioration the damage caused to materials of economic importance due to biological (mainly microbial) processes.

Biofilm a complex system of microorganisms and their surrounding polysaccharide matrix.

Biomass the total amount of cellular material in a system.

Bioreactor a fermentation vessel for the controlled growth of microoganisms.

Bioremediation the use of biological processes to improve a specific environment, such as by the removal of a pollutant.

Calvin cycle a pathway for the fixation of carbon dioxide, used by photosynthetic organisms and some chemolithotrophs.

Capsid the protein coat of a virus particle.

Capsomer a protein subunit of a viral capsid.

Capsule a clearly defined polysaccharide layer surrounding the cell of certain procaryotes.

Carcinogen an agent capable of causing cancer.

Catabolism those reactions that break down large molecules, usually coupled to a release of energy.

Catabolite repression the mechanism by which the presence of a preferred nutrient (generally glucose) has the effect of preventing the synthesis of enzymes that metabolise other nutrients.

Central Dogma of biology the proposal that information (= genetic) flow in organisms is in one direction only, from DNA to RNA to protein.

Centromere the central region of the chromosome that ensures correct distribution of chromosomes between daughter cells during cell division.

Chemotroph an organism that obtains its energy from chemical compounds.

Chloroplast a chlorophyll-containing organelle found in photosynthetic eucaryotes.

Chromosome a nuclear structure on which most of a eucaryotic cell'sgenetic information (DNA) is carried, in association with specialised proteins called histones. The nucleoid of procaryotes (q.v.) is also often referred to as a chromosome.

Cilium (pl. cilia) a short motile hair-like structure found on the surface of some eucaryotic cells.

Citric acid cycle see Tricarboxylic acid cycle.

Clamp connection a mechanism, unique to members of the Basidiomycota, for ensuring the maintenance of the dicaryotic state.

Cloning the production of multiple copies of a specific DNA molecule. The term is also used to describe the production of genetically identical cells or even organisms.

Coccus (pl. cocci) a spherically-shaped bacterium.

Codon a sequence of three nucleotide bases that corresponds to a specific amino acid.

Coenocytic containing many nuclei within a single plasma membrane.

Coenzyme a loosely-bound organic cofactor that influences the activity of an enzyme.

Cofactor a non-protein component of an enzyme (often a metal ion) essential for its normal functioning.

Commensal an organism that lives in or on another organism, deriving some benefit from the association but not harming the other party.

Commensalism an association between two species from which one participant (the commensal) derives benefit, and the other is neither benefited nor harmed.

Competence (of a bacterial cell): the state of being able to take up naked DNA from outside the cell.

Compound a substance comprising the atoms of two or more elements. Conidiophore an aerial hypha that bears conidia.

Conidium (conidiospore) an asexual spore, found in members of the Ascomycota and Actinomycetes. Often forms chains.

Conjugation a process of genetic transfer involving intimate contact between cells and direct transfer of DNA across a sex pilus.

Consumer a heterotroph that derives energy from the consumption of other organisms.

Continuous culture a microbial culture in which nutrient concentrations and other conditions are kept constant by the addition of fresh medium and the removal of old.

Contractile vacuole a fluid-filled vacuole involved in the osmoregulation of certain protists.

Cosmid a hybrid cloning vector capable of accommodating inserts of up to 50kb.

Covalent bond a bond formed by the sharing of a pair of electrons between atoms.

Cyanobacteria a group of mostly unicellular procaryotes that carry out oxygenic photosynthesis. Commonly known as the blue-greens.

Decimal reduction time (D value) the time needed to reduce a cell population by a factor of ten (i.e. to kill 90% of the population) using a particular heat treatment.

Decomposer an organism that breaks down the remains and waste products of producers and consumers.

Defined medium a medium whose precise chemical composition is known.

Denitrification the reduction, under anaerobic conditions, of nitrite and nitrate to nitrogen gas.

Diauxic growth a form of growth that has two distinct phases due to one carbon source being used preferentially before a second.

Dicaryon a structure formed by two cells whose contents, but not nuclei, have fused.

Differential medium a medium that allows colonies of a particular organism to be differentiated from others growing in the same culture.

Differential stain a stain that employs two or more dyes to distinguish between different cellular structures or cell types.

Dimorphic existing in two distinct forms.

Dioecious having male and female reproductive structures on separate individuals. Diploid having two sets of chromosomes.

Disaccharide a carbohydrate formed by the joining of two monosaccharides.

Disc diffusion method a method for assessing the antimicrobial properties of a substance.

Disinfection the elimination or inhibition of pathogenic microorganisms in or on an object so that they no longer pose a threat.

Dissimilatory sulphate reduction the reduction of sulphate to hydrogen sulphide by obligate anaerobes, using either an organic compound or hydrogen gas as electron donor.

DNA library a collection of cloned DNA fragments. Domain the highest level of taxonomic grouping.

Eclipse period the stage of a viral replication cycle in which no complete viral particles are present in the infected host cell.

Ecosystem the organisms of a particular habitat, together with their inanimate surroundings.

Ectoparasite a parasite that attaches to the outside of its host. Electron a subatomic particle carrying a negatively charge.

Electron transport chain a series of donor/acceptor molecules that transfer electrons from donors (e.g. NADH) to a terminal electron acceptor (e.g. O2).

Embden Meyerhof pathway see Glycolysis.

Endoparasite a parasite that fully enters its host and lives inside it.

Endoplasmic reticulum a tubular network found in the cytoplasm of eucaryotic cells.

Endospore a highly resistant spore found within certain bacteria.

Enrichment culture a culture that uses a selective medium to encourage the growth of an organism present in low numbers.

Entner-Doudoroff Pathway an alternative pathway for the oxidation of glucose, producing a mixture of pyruvate and glyceraldehyde-3-phosphate.

Enzyme a cellular catalyst (usually protein), specific to a particular reaction or group of reactions.

Epiphyte an organism that grows on the surface of a plant.

Eucaryote an organism whose cells contain a true nucleus and membrane-bound organelles such as mitochondria and endoplasmic reticulum.

Excision repair a repair mechanism in which damaged sections of DNA are cut out and replaced.

Exon a coding region of a gene. c.f. intron

Expression vector a vector that allows the transcription and translation of a foreign gene inserted into it.

Facilitated diffusion the transport of molecules across a membrane with the help of carrier proteins. Transport takes place down a concentration gradient, and energy is not required.

Facultative anaerobe an organism that can grow in the absence of oxygen, but utilises it when available.

Fastidious (of an organism): unable to synthesise a range of nutrients and therefore having complex requirements in culture.

Fatty Acid a long-chain hydrocarbon chain with a carboxyl group at one end.

Feedback inhibition a control mechanism whereby the final product of a metabolic pathway acts as an inhibitor to the enzyme that catalyses an early step (usually the first) in the pathway.

Fermentation a microbial process by which an organic substrate (usually a carbohydrate) is broken down without the involvement of oxygen or an electron transport chain, generating energy by substrate-level phosphorylation

Flagellum a long hair-like extracellular structure associated with locomotion. Found in both procaryotes and eucaryotes, although each has its own distinctive structure.

F plasmid a plasmid containing genes that code for the construction of the sex pilus, across which it is transferred to a recipient cell.

Frameshift mutation a mutation that results in a change to the reading frame, and thus an altered sequence of amino acids downstream of the point where it occurs.

Fungi a kingdom of non-photosynthetic eucaryotes characterised by absorptive heterotrophic nutrition.

Gamete a haploid reproductive cell arising from meiosis. Fuses with another gamete to form a diploid zygote.

Gametophyte the haploid, gamete-forming stage in a life cycle with alternation of generations.

Gene a sequence of DNA that usually encodes a polypeptide.

Generalised transduction the transfer of a gene from one bacterial cell to another as a result of being inadvertently packaged into a phage particle.

Generation (doubling) time the time taken for a population of cells to double in time under specific conditions.

Genetic code the 64 triplet codons and the corresponding amino acids or termination sequences.

Genome the complete genetic material of an organism. Genotype the genetic make-up of an organism.

Gluconeogenesis a series of reactions by which glucose is synthesised from compounds such as amino acids and lactate.

Glycolysis a series of reactions by which glucose is oxidised to two molecules of pyruvate with the synthesis of two molecules of ATP.

Glycosidic linkage a covalent linkage formed between monosaccharides.

Golgi apparatus an organelle of eucaryotes, comprising flattened membranous sacs.

Gram stain a differential stain that divides bacteria into Gram-positive (purple) or Gram-negative (pink). The reaction depends on the constitution of the organism'scell wall.

Group translocation a form of active transport in which a solute is modified to prevent its escape from the cell.

Haploid having only one set of chromosomes.

Haloduric able to tolerate high salt concentrations.

Halophilic showing a requirement for moderate to high salt concentrations.

Heterotroph an organism that must use one or more organic molecules as its source of carbon.

Hexose a six-carbon sugar.

Hexose monophosphate shunt see Pentose phosphate pathway

Hfr cell a bacterial cell that has a transferred F plasmid integrated into its chromosome.

Histone a basic protein found associated with DNA in eucaryotic chromosomes.

Horizontal transfer the transfer of genetic material between members of the same generation.

Human genome project an international effort to map and sequence all the DNA in the human genome. The project has also involved sequencing the genomes of several other organisms.

Hydrogen bond a relatively weak bond that forms between covalently bonded hydrogen and any electronegative atom, most commonly oxygen or nitrogen.

Hydrophilic ('water-loving'):having an affinity forwater. Hydrophobic ('water-hating'):repelled by water.

Hypha a thread-like filament of cells characteristic of fungi and actinomycetes.

Immersion oil a viscous oil used to improve the resolution of a light microscope at high power.

In vitro = 'in glass',i.e. outside of the living organism, in test tubes etc. In vivo = 'in life',i.e. within the living organism.

Inoculum the cells used to 'seed' a new culture.

Insertion vector a cloning vector based on phage X that has nonessential genes removed.

Insertional inactivation the insertion of foreign DNA within the gene sequence of a selectable marker in order to inactivate its expression.

Interrupted mating a technique in which the order of gene transfer during conjugation is determined by terminating transfer at different time intervals.

Intron a non-coding sequence within a gene. c.f. exon

Ion an atom or group of atoms that carries a charge due to losing or gaining one or more electrons.

Isogamy the fusion of morphologically identical motile gametes.

Isotope forms of an element, having the same number of protons and electrons but differing in the number of neutrons

Karyogamy the fusion of nuclei from two different cells.

Ketose a sugar molecule that contains a ketone group.

Kinetoplast a specialised structure within the mitochondria of certain flagellated protozoans.

Koch's postulates a set of criteria, proposed by Robert Koch, which must be satisfied in order to link a specific organism to a specific disease.

Krebs cycle see Tricarboxylic acid cycle.

Latent period the period in a viral replication cycle between infection of the host and release of newly synthesised viral particles.

Latent virus a virus that remains inactive in the host for long periods before being reactivated.

Lichen a symbiotic association of a fungus (usually an ascomycete) and an alga or cyanophyte (blue-green).

Limnetic zone a zone of a body of water away from the shore, and where light is able to penetrate.

Lipase an enzyme that digests lipids.

Lithotroph an organism that uses inorganic molecules as a source of electrons.

Littoral zone the region of a body of water situated close to land where the water is sufficiently shallow for sunlight to penetrate to the bottom.

Lysogeny a form of bacteriophage replication in which the viral genome is integrated into that of the host and is replicated along with it. See prophage.

Lytic cycle a process of viral replication involving the bursting of the host cell and release of new viral particles.

Magnetosome a particle of magnetite (iron oxide) found in certain bacteria, allowing them to orient themselves in a magnetic field.

Malting the stage in beer-making in which grain is soaked in water to initiate germination and activate starch-digesting enzymes.

Mashing the stage in beer-making in which soluble material is released from the grain in preparation for fermentation.

Mass number the combined total of protons and neutrons in the nucleus of an element.

Meiosis a form of nuclear division in diploid eucaryotic cells resulting in haploid daughter nuclei.

Merodiploid a genome that is partly haploid and partly diploid.

Mesophile an organism that grows optimally at moderate temperatures (20-45°).

Messenger RNA (mRNA) a form of RNA that is synthesised as a complementary copy of the template strand of DNA.

Methanotroph a bacterium capable of using methane as a carbon and energy source.

Michaelis constant (Km) the concentration of substrate in an enzyme reaction that results in a rate of reaction equal to one half of the maximum.

Mineralisation the breakdown of organic matter to carbon dioxide and inorganic compounds.

Minimum inhibitory concentration (MIC) the lowest concentration of an antimicrobial substance that prevents growth of a given organism.

Mismatch repair a DNA repair system that replaces incorrectly inserted nucleotides.

Missense mutation a mutation that alters the sense of the message encoded in the DNA, resulting in an incorrect amino acid being incorporated.

Mitochondrion a spherical to ovoid organelle found in eucaryotes. The site of ATP generation via TCA cycle and oxidative phosphorylation.

Mitosis a form of nuclear division in eucaryotic cells, resulting in daughter nuclei each with the same chromosome complement as the parent.

Monoecious having reproductive structures of both sexes on the same individual.

Monosaccharide the simplest from of carbohydrate molecule.

Most probable number (MPN) a statistical method of estimating microbial numbers in a liquid sample based upon the highest dilution able to support growth.

mRNA see Messenger RNA

Mutagen a chemical or physical agent capable of inducing mutations.

Mutation any heritable alteration in a DNA sequence. It may or may not have an effect on the phenotype.

Mutualism an association between two species from which both participants derive benefit.

Mycelium a tangled mass of branching hyphae.

Mycorrhiza a mutualistic relationship between a fungus and a plant root. Mycosis a disease caused by a fungus.

Neutron a subatomic particle carrying neither positive nor negative charge.

Nitrification the two-step process by which ammonia is oxidised to nitrite and then to nitrate.

Nonsense codon see stop codon.

Nonsense mutation a mutation that results in a 'stop' codon being inserted into the mRNA at the point where it occurs, and the premature termination of translation.

Nosocomial infection an infection that is acquired in hospital or other healthcare setting.

Nuclear membrane the double membrane surrounding the nucleus of a eucaryotic cell.

Nucleocapsid the genome of a virus and its surrounding protein coat.

Nucleoid another name for the bacterial chromosome. The site of most of a procaryotic cell's DNA.

Nucleolus a discrete region of the eucaryotic nucleus, where ribosomes are assembled.

Nucleotide the building block of nucleic acids, comprising a pentose sugar, a nitrogenous base and one or more phosphate groups.

Nucleus the central, membrane-bound structure in eucaryotic cells that contains the genetic material. Also, the region of an atom that contains the protons and neutrons.

Obligate anaerobe an organism that is incapable of growth in the presence of oxygen.

Okazaki fragments discontinuous fragments of single-stranded DNA synthesised complementary to the lagging strand during DNA replication.

Oncogene a gene associated with the conversion of a cell to a cancerous form.

Oogamy the fusion of a small, motile sperm cell and a larger, immobile egg cell.

Operon a group of related genes under the control of a single operator sequence.

Organotroph an organism that uses organic molecules as a source of electrons.

Outer membrane the outermost part of the Gram-negative cell wall, comprising phospholipids and lipopolysacchride.

Oxidation a chemical reaction in which an electron is lost.

Oxygenic photosynthesis a form of photosynthesis in which oxygen is produced; found in algae, cyanobacteria (blue greens) and also green plants.

Parasitism an association between two species from which one partner derives some or all of its nutritional requirements by living either in or on the other (the host), which usually suffers harm as a result.

Pasteurisation a mild heating regime used to destroy pathogens and spoilage organisms present in food and drink, especially milk.

Pathogen an organism with the potential to cause disease.

Pellicle a semi-rigid structure composed of protein strips found surrounding the cell of certain unicellular protozoans and algae.

Pentose a five-carbon sugar.

Pentose phosphate pathway a secondary pathway for the oxidation of glucose, resulting in the production of pentoses that serve as precursors for nucleotides.

Peptide bond the bond formed between the amino group of one amino acid and the carboxyl group of another.

Peptidoglycan a polymer comprising alternate units of N-acetylmuramic acid and N-acetylglucosamine that forms the major constituent of bacterial cell walls.

Phagemid a hybrid cloning vector, comprising elements of plasmid and phage.

Phagocytosis the ingestion and digestion of particulate matter by a cell, a process unique to eucaryotes.

Phenol coefficient a measure of the efficacy of a disinfectant against a given organism, compared to that of phenol.

Phenotype the observable characteristics of an organism.

Phospholipid an important constituent of all membranes, comprising a triacylglycerol in which one fatty acid is replaced by a phosphate group.

Phosphorylation the addition of a phosphate group.

Photophosphorylation the synthesis of ATP using light energy.

Photoreactivation a DNA repair mechanism involving the light-dependent enzyme DNA photolyase.

Photosynthesis a process by which light energy is trapped by chlorophyll and converted to ATP, which is used to drive the synthesis of carbohydrate by reducing CO2.

Phototroph an organism that is able to use light as its source of energy.

Phylogenetic relating to the evolutionary relationship between organisms.

Phytoplankton the collective term used to describe the unicellular photosynthesisers, including cyanobacteria, dinoflagellates, diatoms and single-celled algae.

Pilus (pl. pili) a short, hair-like appendage found on surface of procaryotes and assisting with attachment. Specialised sex pili (q.v.) are involved in bacterial conjugation.

Plankton the floating microscopic organisms of aquatic systems. Plasma membrane the membrane that surrounds a cell.

Plasmid a small, self-replicating loop of extrachromosomal DNA, found in bacteria and some yeasts. Specially engineered forms are used as vectors in gene cloning.

Plasmodium a mass of protoplasm containing several nuclei and bounded by a cytoplasmic membrane.

Plasmogamy the fusion of the cytoplasmic content of two cells.

Plasmolysis the shrinkage of the plasma membrane away from the cell wall, due to osmotic loss of water from the cell.

Point mutation a mutation that involves the substitution of one nucleotide by another.

Polar having unequal charge distribution, caused by unequal sharing of atoms.

Polymerase chain reaction (PCR) a technique that selectively replicates a specific DNA sequence by means of in vitro enzymatic amplification.

Polypeptide a chain of many amino acids joined together by peptide bonds.

Polyribosome (polysome) a chain of ribosomes attached to the same molecule of mRNA.

Polysaccharide a carbohydrate polymer of monosaccharide units.

Primary producer an autotroph that obtains energy from the sun or chemical sources.

Primer a short sequence of single-stranded DNA or RNA required by DNA polymerase as a starting point for chain extension.

Prion a self-replicating protein responsible for a range of neurodegenerative disorders in humans and mammals

Procaryote an organism lacking a true nucleus and membrane-bound organelles.

Profunda! zone the deepest part of a body of water, where the sun is unable to penetrate

Promoter a sequence upstream of a gene, where RNA polymerase binds to initiate transcription.

Prophage the DNA of a temperate phage that has integrated into the host genome. It remains inactive whilst in this form.

Prostheca a stalked structure formed by an extension of the cell wall and plasma membrane of certain bacteria.

Prosthetic group a non-polypeptide component of a protein, such as a metal ion or a carbohydrate.

Protease an enzyme that digests proteins.

Protista a eucaryotic kingdom, comprising mostly unicellular organisms.

Protocooperation a form of mutualistic relationship that is not obligatory for either partner.

Proton a positively-charged subatomic particle. Protoplast a cell that has had its cell wall removed. Prototroph the normal, nonmutant form of an organism.

Protozoa a group of single celled eucaryotes with certain animal-like characteristics.

Pseudomurein a modified form of peptidoglycan found in some archaean cell walls.

Pseudopodium a projection of the plasma membrane of the amoebas that causes the cell to change shape and allows movement.

Psychrophile an organism that grows optimally at low temperatures (<15°).

Psychrotroph an organism that is able to tolerate low temperatures, but grows better at more moderate values.

Reading frame the way in which a sequence of nucleotides is read in triplets, depending on the starting point.

Real image an image that can be projected onto a flat surface such as a screen.

Recombinant DNA DNA that comprises material from more than one source.

Recombination any process that results in new combinations of genes.

Redox potential (Eo) the tendency of a compound to lose or gain electrons.

Reduction a chemical reaction in which an electron is gained.

Refractive index the ratio between the velocity of light as it passes through a substance and its velocity in a vacuum.

Regulatory gene a gene whose protein product has an effect in controlling the expression of other genes.

Replacement vector a cloning vectors based on phage X, in which a central section of nonessential DNA is replaced by the insert DNA.

Replication fork a Y-shaped structure formed by the separating strands of DNA during replication.

Repressor protein a protein that prevents transcription of a gene by binding to its operator.

Resolution the capacity of an optical instrument to discern detail.

Restriction endonuclease an enzyme of microbial origin that cleaves DNA at a specific nucleotide sequence.

Reverse transcriptase an enzyme found in retroviruses that can synthesise DNA from an RNA template.

Rhizosphere the region around the surface of a plant's root system.

Ribosomal RNA (rRNA) a form of RNA that forms part of the structure of ribosomes.

Ribosome an organelle made up of protein and RNA, found in both procaryotes and eucaryotes. The site of protein synthesis.

rRNA see Ribosomal RNA

Saprobe an organism that feeds on dead and decaying organic materials. Previously termed saprophyte.

Saturated fatty acid a fatty acid that has only single covalent bonds between adjacent carbon atoms. (c.f. unsaturated)

Secondary metabolite a substance produced by a microorganism after the phase of active growth has ceased.

Selectable marker a gene that allows cells containing it to be identified by the expression of a recognisable characteristic.

Selective medium a medium that favours the growth of a particular organism or group of organisms, often by suppressing the growth of others.

Semi-conservative replication the process of DNA replication by which each strand acts as a template for the synthesis of a new complementary strand. Each resultant double stranded molecule thus comprises one original strand and one new one.

Septate separated by septa or cross-walls.

Sex pilus a narrow extension of the bacterial cell, through which genetic material is transferred during conjugation.

Shuttle vector a cloning vector that can replicate in both bacterial and yeast host cells.

Silent mutation a mutation that has no effect on the amino acid encoded by the triplet.

Single-cell protein (SCP) bacteria and yeast grown in bulk for use as a protein-rich food supplement.

Slime layer a diffuse and loosely attached polysaccharide layer surrounding the cell of certain procaryotes.

Specialised transduction the transfer of a limited selection of genes due to imprecise excision of a prophage in a lysogenic infection cycle.

Sporangiophore a specialised aerial hypha that bears the sporangia.

Sporangium a structure inside which spores develop.

Spore a resistant, non-motile reproductive cell.

Sporophyte the diploid, spore-forming stage in a life cycle with alternation of generations.

Sporozoite a motile infective stage of members of the Sporozoa that gives rise to an asexual stage within the new host.

Sterilisation the process by which all microorganisms present on or in an object are destroyed or removed.

Steroid a member of a group of lipids based on a four-ring structure. Stop codon use definition below.

Substrate level phosphorylation the synthesis of ATP by the direct transfer of a phosphate group from a phosphorylated organic compound to ADP.

Symbiosis a close physical association between two species from which special benefits may accrue for one or both parties.

The term is sometimes used specifically to describe such a relationship in which both parties derive benefit (see mutualism).

Tautomerism the ability of a molecule such as a nucleotide base to exist in two alternative forms.

Taxonomy the science of naming and classifying living (and once-living) organisms.

Temperate phage a bacteriophage with a lysogenic replication cycle.

Terminator a sequence of DNA that indicates transcription should stop.

stop codons one of the three triplet sequences (also called nonsense codons) that indicate translation should stop.

Thallus a simple vegetative plant body showing no differentiation into root, stem and leaf.

Therapeutic index a measure of the selective toxicity of a chemotherapeutic agent.

Thylakoid a photosynthetic membrane found in chloroplasts or free in the cytoplasm (in cyanobacteria). It contains photosynthetic pigments and components of the electron transport chain.

Total cell count a method that enumerates all cells, living and dead.

Trace element an element required in minute amounts for growth.

Transamination a reaction involving the transfer of an amino group from one molecule to another.

Transcription the process by which single-stranded mRNA is synthesised from a complementary DNA template.

Transduction the bacteriophage-mediated transfer of genetic material between bacteria.

Transformation the uptake of naked DNA from the environment and its integration into the host genome.

Transposable elements a sequence of DNA that is able to relocate to another position on the genome.

Transition a mutation in which a purine replaces a purine or a pyrimidine replaces a pyrimidine.

Translation the process by which the message encoded in mRNA is converted into a sequence of amino acids.

Transfer RNA (tRNA) a form of RNA that carries specific amino acids to the site of protein synthesis.

Transversion a mutation in which a purine replaces a pyrimidine, or a pyrimidine replaces a purine.

Triacylglycerol a lipid formed by the joining of three fatty acids to a molecule of glycerol.

Tricarboxylic acid cycle a series of reactions that oxidise acetate to CO2, generating reducing power in the form of NADH and FADH2 for use in the electron transport chain. Also known as citric acid cycle or Krebs cycle.

Triose a three-carbon sugar.

tRNA see Transfer RNA

Tyndallisation a form of intermittent steam sterilisation.

Undefined or complex medium a medium whose precise chemical composition is not known.

Unsaturated fatty acid a fatty acid that contains one or more double bonds between adjacent carbon atoms.

Vaccination inoculation with a vaccine to provide protective immunity.

Vaccine a preparation of dead or inactivated living pathogens or their products used to provide protective immunity.

Vector a self-replicating DNA molecule used in gene cloning. The sequence to be cloned is inserted into the vector, and replicated along with it.

Viable cell count a method that enumerates only those cells capable of reproducing to form a visible colony.

Virtual image an image that has no physical existence in space, and cannot be projected onto a screen.

Virion a complete, intact viral particle

Viroid a plant pathogen that comprises only ssRNA and does not code for protein product.

Virulent phage a bacteriophage with a lytic replication cycle.

Virus a submicroscopic, noncellular parasite, comprising protein and RNA or DNA.

Wildtype the normal, nonmutant form of an organism or gene.

Wobble the degree of flexibility allowed in the third base in a codon when pairing with tRNA. The wobble hypothesis explains how a single tRNA can pair with more than one codon.

Yeast artificial chromosome (YAC) a cloning vector able to accommodate inserts of several hundred kb in size.

Z value the increase in temperature required to reduce the D value (q.v.) by a factor of ten.

Zoonosis a disease normally found in animals, but transmissible to humans under certain circumstances.

Zoospore a flagellated, asexual spore.

Zygospore a thick-walled resistant diploid structure formed by members of the Zygomycota.

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10 Ways To Fight Off Cancer

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