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Biology Glossary - Z

Z: The factor 2.3(RT/F)

 A left-handed helical form of dsDNA (cf. DNA) first observed in oligomers of alternating deoxycytidine (dC) and deoxyguanosine (dG) in the presence of high salt concentrations or ethanol. In these oligomers the strands are connected by Watson–Crick base pairing, the sugar–phosphate backbones form an irregular zig-zag (hence Z -DNA), there are ca. 12 bp/turn, and the bases are relatively peripheral with the N7 and C8 positions of guanine exposed; there is a single very deep helical groove corresponding to the minor groove of B-DNA (see DNA). Stretches of alternating dC and dG in a plasmid can undergo transition from right- to left-handed helical form
under physiological levels of ionic strength and super helical density; the transition is driven by the torsional strain of negative super coiling and is facilitated by C5 methylation of cytidine.Whether or not Z-DNA occurs in vivo remains controversial.
Unlike B-DNA, Z-DNA is strongly immunogenic, and monoclonal antibodies have been used for its detection in cells; however, the specificity of these antibodies for Z-DNA is uncertain. The isolation of proteins which preferentially bind Z-DNA rather
than B-DNA provides circumstantial evidence for the existence of Z-DNA in vivo.

Z ring
see cell cycle (b).

Z scheme
see photosynthesis.

z value
 The increase in temperature (°C) required for a 10-fold decrease in the D Value.

Zadoks’ code
 (Zadoks, Chang and Konzak decimal code) A code, designed primarily for computer use, in which the various growth stages of cereals are represented by numbers between 0 and 100: 0–9, germination; 10–19, seedling growth; 20–29, tillering; 30–39, stem elongation; 40–49, ‘booting’ (swelling of the leaf sheath enclosing the
developing ear); 50–59, ear emergence; 60–69, flowering; 70–79, ‘milky’ stage of grain development; 80–89, ‘doughy’ stage of grain development; 90–99, grain ripening.

 see nucleoside reverse transcriptase inhibitors.

see hyphomycetes; see also textile spoilage.

An anti-influenza drug: a sialic acid analogue which can inhibit the viral
Neuraminidase in influenza virus types A and B; the drug is inhaled

Zoster-associated pain: see herpes zoster.

zaragozic acids
Metabolites of certain fungi which are potent inhibitors of the enzyme squalene synthase; they have potential uses as antifungal agents and/or as therapeutic agents for lowering the levels of plasma cholesterol.

Zidovudine (see AZT).

see zearalenone.

(F-2 toxin) A mycotoxin produced by Gibberella zeae (Fusarium graminearum) growing e.g. on damp cereal feedstuffs. It has oestrogenic activity and can cause hyperoestrogenism (manifest by vulvovaginitis and infertility) in sows;cattle and poultry can be affected, though to a lesser extent.

Zearalenone can also act as a regulatory hormone in the sexual cycle of Gibberella. Chemical reduction of zearalenone yields azearalenol,which is 4.8 times more oestrogenic than zearalenone and has anabolic properties; it is used to promote rapid weight gain in cattle and as an oestrogen substitute in postmenopausal women.

A naturally occurring Cytokinin: 6-(4-hydroxy-3-methylbut-2-enyl)-aminopurine. Its derivatives (e.g. zeatin riboside) also function as cytokinins.

see carotenoids.

zeaxanthin rhamnoside
see xanthobacter.

 (Zta) Z EBV replication activator: the protein product of (immediate-early) viral gene bzlf-1 which promotes replication of the EPSTEIN–BARR VIRUS in latently infected B lymphocytes. ZEBRA can be induced by treating latently infected B cells with e.g. anti-immunoglobulin, corticosteriods or ‘phorbol ester’ (12-O-tetradecanoylphorbol-13-acetate, TPA).The lytic cycle in latently infected B cells is also promoted by another transcription factor, Rta, encoded by the immediateearly viral gene brlf-1 ; it has been reported that the promoter of brlf-1 is activated by acetylation of histones.

See opalinata.

Zenker’s fluid (modified)
A fixative: mercuric chloride (5 g) and potassium dichromate (2.5 g) in distilled water (100 ml) supplemented immediately before use with glacial acetic acid (5 ml).

see quaternary ammonium compounds.

Zeta Plus filter
 see filtration.

(zeta potential; electrokinetic potential)
Of e.g. a bacterial cell, or a charged colloid particle: the electrical potential at the surface of shear – i.e., the surface of the cell or particle, including adherent counterions and water molecules – which tends to move relative to the surrounding medium when an external electrical field is applied; it is a determinant of the electrophoretic migration rate of a cell etc. In media of neutral or alkaline pH most bacteria carry a surface charge of negative polarity – due to the ionization of surface groups. In many cases the isoelectric point of a bacterium is ca. 3.0; at or near this pH such bacteria tend toagglutinate spontaneously.

Zetapor membrane filter
see filtration.

 An early term for a cell or structure in which karyogamy ends dikaryophase.

see laver.

Syn. AZT (q.v.).

Ziehl–Neelsen’s stain
 An acid-fast stain. A heat-fixed smear is flooded with concentrated carbolfuchsin, heated and kept steaming (not boiling) for 5 min, allowed to cool, and rinsed in running water; the slide is then passed through several changes of acid-alcohol (e.g. 3% v/v conc. HCl in 95% ethanol), washed in water, and counterstained with e.g. 0.5% aqueous malachite green. After a final washing in water the smear is dried and examined by microscopy. Acid-fast organisms stain red, others green.

Ziemann’s dots
In erythrocytes infected with Plasmodium malariae: fine dots sometimes observed on heavy staining with Romanowsky stains.

Zika virus
see flaviviridae.

(a) (microbial requirement) zinc is a heavy metal which is needed, in trace amounts, for the activity of a number of microbial enzymes – e.g. Alcohol dehydrogenase; de-acetylase (encoded by gene 1pxc in escherichia coli, and involved in lipid A synthesis); some b-lactamases and superoxide dismutases; the uvr a protein involved in dna repair; the zinc-endopeptidase tetanospasmin; and carbonic anhydrase.

(b) (as an antimicrobial agent) In effective concentrations, zinc, and certain of its compounds, are useful antimicrobial agents. For example, zinc undecylenate  and zinc oxide have been used for treating certain superficial mycoses (e.g. athlete’s foot), and zinc oxide is used as a mould inhibitor in paints. Zinc naphthenate can replace copper naphthenate as a wood preservative but is apparently less effective. Zinc dimethyldithiocarbamate has been used as a preservative in rubber (it also serves as a vulcanization catalyst) and as an agricultural antifungal agent (ziram – see also ZINEB). The precise mechanism of antimicrobial action may vary with organism; thus, e.g. zinc appears initially to cause membrane damage in Saccharomyces cerevisiae but may act by inhibiting intracytoplasmic proteins in another yeast, Sporobolomycesroseus.

(c) (zinc chelation) The mammalian protein calprotectin is a zinc-chelating agent whose bacteriostatic action presumably reflects its ability to sequester zinc ions

see tetanospasmin.

zinc sulphate flotation
 see flotation.

zinc undecylenate
see undecylenic acid.

 see azole antifungal agents.

(dithane z-78) zinc ethylenebisdithiocarbamate; this important agricultural antifungal agent is used to control a wide range of plant pathogens, e.g. botrytis spp, fulvia fulva (cladosporium fulvum), peronospora spp, phytophthora infestans; it may be prepared as a wettable powder – or may beprepared in the field by mixing nabam, zinc sulphate and lime.

zipa protein
 see cell cycle (b).

 see food poisoning (yersinia).


In coccidia: any of a range of stages in the life cycle – e.g.cystozoite, endozoite, sporozoite etc.

zonal centrifugation
 see centrifugation.

 see phaeophyta.

zone centrifugation
 See centrifugation.

zone lines
 In decaying wood: dark lines which are the edges of sheets of pigmented fungal tissues in the wood.In wood rotted by e.g. Phellinus weirii the coloration is due to a melanin-like pigment which apparently inhibits the growth of microorganisms
antagonistic to P. Weirii

zoned reserve systems
Habitat areas that are protected from human alteration and surrounded by lands that are used and more extensively altered by human activity.

an animal symbiont. (cf. phycozoan.)

Green endosymbiotic algae present in various phycozoan associations. For example, chlorella occurs e.g. In certain protozoa (e.g. Foraminifera, mayorella viridis, paramecium bursaria, stentor polymorphus), the freshwater sponge spongilla sp, the coelenterate hydra viridis, the freshwater flatworm dalyellia viridis, and the freshwater clam anodonta. The phycobiont generally supplies the zoobiont with products of photosynthesis (e.g. Maltose in hydra and Paramecium, glucose in spongilla), although the zoobiont may continue to feed. (see also elysia; cf. Zooxanthellae.)

 Flagellates of the zoomastigophorea.

 (zooglea) A mass or film of cells embedded in a slimy matrix; zoogloeae are formed e.g. by Zoogloea ramigera.

 A genus of gram-negative, aerobic, chemoorganotrophicbacteria (family pseudomonadaceae) which occur e.g. In organically polluted freshwater habitats, and in aerobically treated sewage .
 (microbiol.) (1) A motile spore. (2) Of a stalked ciliate(e.g. Vorticella): the cell body, as opposed to the stalk.

[Gk. zoe, life + logos, a discourse]
The study of animals.

[Gk. zoe, life + plankton, wanderer]
A collective term for the nonphotosynthetic organisms present in plankton.

zoom microscope
 A compound microscope in which magnification can be varied continuously over a range of values.

 A class of flagellate protozoa (subphylum mastigophora) which lack chloroplasts and which are non-photosynthetic.

 Any infectious disease which can be contracted by man and in which the pathogen is normally maintained in a reservoir consisting of animal (i.e. non-human) population(s).

 pertaining to zoonosis.

An order of fungi (class zygomycetes) which occur e.g. in soil and water, and which are parasitic on e.g. certain amoebae, nematodes, and fungi; the organisms form zygospores and give rise to asexual spores which are not forcibly discharged. Genera: e.g. Bdellospora, Cochlonema, Piptocephalis, Rhopalomyces, and Stylopage
 A genus of fungi of the peronosporales; Z. Insidians is an aquatic species which captures and feeds on rotifers.

 Refers to a parasite or pathogen which preferentially infects animals.

 See entomophthorales.

 See plankton.

a sporangium in which motile spores are formed.

 a motile (flagellated) spore.

 See Peritrichia.

 See Zooxanthellae.

Endosymbiotic dinoflagellates found in various marine invertebrates, including sea anemones (e.g. Anthopleura), giant clams (Tridacna), jellyfish (Cassiopeia), reefforming tropical corals, and members of the FORAMINIFERIDA and RADIOLARIA. (The loss of zooxanthellae from corals is a useful indicator of stress due e.g. to pollution).All such endosymbiotic dinoflagellates have been regarded as belonging to a single species, variously called Symbiodinium microadriaticum, Gymnodinium microadriaticum, or Zooxanthella microadriatica, but according to one report there are probably several distinct species. (See also phycozoan.) [Evidence for heterotrophy by zooxanthellae in the sea anemone Aiptasia pulchellaand its detrimental effects on the host under certain conditions].

 syn. herpes zoster.

zoster-associated pain (ZAP)
see herpes zoster.

Zot toxin
 (Vibrio cholerae) see bacteriophage CTX8.

syn. acyclovir.

See myxosporea.


 Glucose 6-phosphate dehydrogenase
(see Hexose Monophosphate Pathway).

zwoegerziekte virus
(zwogerziekte virus)
See Lentivirinae.

 A genus of freshwater, unbranched filamentous green algae related to Spirogyra; each cell contains two stellate chloroplasts. Akinetes may be formed.

 Agenus of filamentous, heterothallic fungi that include the teleomorphic stages of Candida hellenica, C. inositophila and C. steatolytica; type species: Z. hellenicus.

 See Diatoms.

 A genus of filamentous green algae related to Spirogyra. The filaments contain a purple pigment and grow e.g. on damp peaty soils; some species are thermophilic, forming dense purple mats near hot springs.


A class of fungi of the zygomycotina; most zygomycetes are terrestrial saprotrophs, but some are parasites or pathogens of animals (including insects), plants, and other fungi. The typical thallus is a well developed, branched, coenocytic (aseptate) mycelium, but some species form a septate mycelium, and some (see mucorales) are dimorphic fungi; the cell wall contains chitin and/or chitosan. Characteristic asexual reproductive structures include the sporangium and the sporangiolum. Sexual reproduction typically involves zygospore formation by the fusion of two morphologically similar gametangia; some species exhibit homothallism, some heterothallism.  Orders Dimargaritales (members form merosporangia each containing two spores arranged End-to-end); Endogonales; Entomophthorales; Kickxellales; Mucorales; Zoopagales.


Any of a range of human and animal diseases caused by fungi of the zygomycetes; the term currently includes diseases formerly called phycomycosis (caused by ‘phycomycetes’), mucormycosis (caused by fungi of the mucorales), and entomophthoromycosis (caused by fungi of the entomophthorales). In all zygomycoses the invasive form of the pathogen is an aseptate or sparsely septate, broad (e.g. 6–25 μm diam.), hyaline mycelium; the hyphae may be branched and may assume bizarre forms.

Zygomycosis in man. Subcutaneous zygomycosis, in which a sharply delineated, pain-less nodule develops and grows to form a tumour-like mass, is caused usually by Basidiobolus
haptosporus (= B. meristosporus). Nasofacial zygomycosis is caused by Conidiobolus coronatus and involves the development of tumefactions in the nasal mucosa and adjacent tissues. Rhinocerebral zygomycosis is caused by Rhizopus oryzae and is associated specifically with acidosis due to acute uncontrolled diabetes; infection occurs mainly via the nasal turbinates and  paranasal sinuses, spreading rapidly to the eyes and brain, and the condition is rapidly fatal if untreated. Systemic zygomycosis may involve an initial pulmonary infection which, if untreated, may spread to other internal organs; causal agents include Absidia corymbifera, Conidiobolus incongruus, Cunninghamella bertholletiae.

Zygomycosis in animals. Causal agents include some human pathogens as well as species apparently non-pathogenic in man (e.g. Mortierella spp). Infection may lead e.g. to placentitis followed by abortion (in cattle), or to the formation of granulomatous, tuberculosis-like lesions in lymph nodes, intestines etc (e.g. in pigs and cattle). 

 A subdivision of fungi (division eumycota) which form non-flagellate asexually derived spores and which typically reproduce sexually by gametangial copulation with the formation of zygospores (q.v.). Classes: trichomycetes and zygomycetes.

 a short hyphal branch which develops into a progametangium.

 see mucorales.

 A genus of yeasts (family saccharomycetaceae) in which the cells are globose, ellipsoidal or cylindrical; vegetative reproduction occurs by multilateral budding. Pseudomycelium may be formed. The vegetative cells are predominantly haploid (cf. SACCHAROMYCES). Ascus formation is preceded by conjugation between individual cells (occasionally between a cell and its bud); asci are persistent.
Ascospores: globose to ellipsoidal, 1–4 per ascus. Sugars are fermented vigorously; NO−3 is not assimilated. Eight species are recognized: Z. bailii (formerly e.g. Saccharomyces elegans), Z. bisporus, Z. cidri, Z. fermentati, Z. florentinus, Z. microellipsoides, Z. mrakii, and Z. rouxii (anamorph: Candida mogii ; numerous synonyms, including e.g. Saccharomyces rouxii ).

 see zygospore.

A thick-walled, sexually-derived resting spore characteristic of fungi of the zygomycotina. (zygospores are apparently not formed by e.g. Members of the saksenaeaceae or of the amoebidiales.) The fusion of two gametangia (see progametangium) gives rise to a prozygosporangium which develops into a zygosporangium having a thick, multilayered, often highly ornamented wall; in at least some zygomycetes the zygospore is known to develop as a separate structure within the zygosporangium.the term ‘zygospore’ has been traditionally used to refer to the zygosporangium together with its enclosed zygospore.

(zi-goat) [Gk. zygon,yolk, pair]
The diploid product of the union of haploid gametes in conception; a fertilized egg.

zygotene stage
 see meiosis.

zygotic induction
 The induction of a prophage when a chromosome containing that prophage is transferred from a lysogenic conjugal donor (see lysogeny and bacterial conjugation) to a recipient not lysogenized by the same (or a closely related) bacteriophage; the induction occurs as a result of the absence of a phage repressor protein in the recipient cell.

zygotic meiosis
Meiosis, in a zygote, preceding the formation of haploid vegetative cells in a life cycle in which haplophase predominates. (cf. Gametic meiosis.)

Old term for the enzyme fraction isolated from disrupted yeast cells which is capable of catalysing alcoholic fermentation.

A subpopulation within a given taxon (e.g. genus) distinguished on the basis of one or more isoenzymes.

 (proenzyme) An inactive enzyme precursor that is usually converted to the active form of the enzyme by proteolytic cleavage.

 Refers to those (predominantly transient or alien) microorganisms in a given environment (e.g. soil) which exhibit an upsurge in growth (and hence in numbers or biomass) on those occasions when the levels of nutrients increase, or when a particular substrate becomes available; in the absence of suitable levels of nutrients, relatively small numbers of such organisms may be capable of existence, in that environment, in a dormant or starvation-resistant stage

(1) A medium (e.g. a starch gel strip) which has been used for the electrophoresis of a cell homogenate and which has been subsequently stained to detect or quantify a given enzyme.
 (2) A table showing the results of tests which determine the ability of one or more organisms to ferment each of a range
of carbohydrates.

 A commercial enzyme preparation obtained from culture filtrates of Arthrobacter luteus. It contains endo-(1→3)- b-glucanase activity (‘Z-glucanase’) – which is active against most (1→3)-b-glucans – and also some protease activity (‘Zprotease’)
Zymolyase is used e.g.for investigating fungal (particularly yeast) cell wall structure,for preparing yeast sphaeroplasts, etc.

 A genus (incertae sedis) of oxidase-negative, catalase-positive, chemoorganotrophic, Gram-negative bacteria which occur e.g. as spoilage organisms in alcoholic beverages (see e.g. CIDER spoilage) and which are used in specific fermentations.

An insoluble polysaccharide, found in the cell wall incertain yeasts, which promotes complement fixation via the alternative pathway.

A biotype characterized on the basis of a zymogram.

 A genus of fungi (order Sphaeropsidales) which include Gnomonia (Zythia) fragariae, a pathogen of the strawberry plant. Elongated conidia are formed in light-coloured pycnidia.

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