| leader peptide | <molecular biology> In the regulation of gene expression for enzymes concerned with amino acid synthesis in prokaryotes, the leader sequence codes for the leader peptide that contains several residues of the amino acid being regulated. Transcription is closely linked to translation and if translation is retarded by limited supply of amino acyl tRNA for the specific amino acid, the mode of transcription of the leader sequence permits full transcription of the operon genes, otherwise complete transcription of the leader sequence prematurely terminates transcription of the operon. (18 Nov 1997) |
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| leader sequence | <molecular biology> In the regulation of gene expression for enzymes concerned with amino acid synthesis in prokaryotes, the leader sequence codes for the leader peptide that contains several residues of the amino acid being regulated. Transcription is closely linked to translation and if translation is retarded by limited supply of amino acyl tRNA for the specific amino acid, the mode of transcription of the leader sequence permits full transcription of the operon genes, otherwise complete transcription of the leader sequence prematurely terminates transcription of the operon. (18 Nov 1997) |
| leader sequences | Sequences at the end of either nucleic acids (DNA and RNA) or proteins that must be processed off to allow for a specific function of the mature molecule. (05 Mar 2000) |
| leadership | <psychology> The function of directing or controlling the actions or attitudes of an individual or group with more or less willing acquiescence of the followers. (25 Jun 1999) |
| leadhillite | <chemical> A mineral of a yellowish or greenish white colour, consisting of the sulphate and carbonate of lead; so called from having been first found at Leadhills, Scotland. Source: Websters Dictionary (01 Mar 1998) |
| leading edge | The initial part of a wave form at maximum slope. (05 Mar 2000) |
| leading lamella | <cell biology> Anterior region of a crawling cell, such as a fibroblast, from which most cytoplasmic granules are excluded. (18 Nov 1997) |
| leading strand | The DNA strand that is synthesised continuously during replication Compare: lagging strand. (09 Oct 1997) |
| leadwort | <botany> A genus of maritime herbs (Plumbago). P. Europaea has lead-coloured spots on the leaves, and nearly lead-coloured flowers. Source: Websters Dictionary (01 Mar 1998) |
| leaf | To shoot out leaves; to produce leaves; to leave; as, the trees leaf in May. Origin: OE. Leef, lef, leaf, AS. Leaf; akin to S. Lf, OFries. Laf, D. Loof foliage, G. Laub,OHG. Loub leaf, foliage, Icel. Lauf, Sw. Lof, Dan. Lov, Goth. Laufs; cf. Lith. Lapas. Cf. Lodge. 1. <botany> A coloured, usually green, expansion growing from the side of a stem or rootstock, in which the sap for the use of the plant is elaborated under the influence of light; one of the parts of a plant which collectively constitute its foliage. Such leaves usually consist of a blade, or lamina, supported upon a leafstalk or petiole, which, continued through the blade as the midrib, gives off woody ribs and veins that support the cellular texture. The petiole has usually some sort of an appendage on each side of its base, which is called the stipule. The green parenchyma of the leaf is covered with a thin epiderm pierced with closable microscopic openings, known as stomata. 2. <botany> A special organ of vegetation in the form of a lateral outgrowth from the stem, whether appearing as a part of the foliage, or as a cotyledon, a scale, a bract, a spine, or a tendril. In this view every part of a plant, except the root and the stem, is either a leaf, or is composed of leaves more or less modified and transformed. 3. Something which is like a leaf in being wide and thin and having a flat surface, or in being attached to a larger body by one edge or end; as: A part of a book or folded sheet containing two pages upon its opposite sides. A side, division, or part, that slides or is hinged, as of window shutters, folding doors, etc. The movable side of a table. A very thin plate; as, gold leaf. A portion of fat lying in a separate fold or layer. One of the teeth of a pinion, especially when small. <zoology> Leaf beetle, any beetle which feeds upon leaves; especially, any species of the family Chrysomelidae, as the potato beetle and helmet beetle. Leaf bridge, a draw-bridge having a platform or leaf which swings vertically on hinges. <botany> Leaf bud, a sawfiy. To turn over a new leaf, to make a radical change for the better in one's way of living or doing. " They were both determined to turn over a new leaf." (Richardson) Source: Websters Dictionary (01 Mar 1998) |
| leaf blight | Any of various diseases which lead to the browning and dropping of a plant's leaves. (09 Oct 1997) |
| leaf-footed | <zoology> Having leaflike expansions on the legs; said of certain insects; as, the leaf-footed bug (Leptoglossus phyllopus). Source: Websters Dictionary (01 Mar 1998) |
| leaf-nosed | <zoology> Having a leaflike membrane on the nose; said of certain bats, especially. Of the genera Phyllostoma and Rhinonycteris. See Vampire. Source: Websters Dictionary (01 Mar 1998) |
| leafage | Leaves, collectively; foliage. Source: Websters Dictionary (01 Mar 1998) |
| leafcup | <botany> A coarse American composite weed (Polymnia Uvedalia). Source: Websters Dictionary (01 Mar 1998) |