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Home >>Botany Dictionary>> Nuclear Fragmentation - Nyctinasty
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Nuclear Fragmentation - Said of formation of two or more por;tions from a nucleus by direct break-up, and not by mitosis.
Nuclear Genes - Genes occurring in the nucleus, in contrast to plasmagenes.
Nuclear Membrane - A layer which is bounding the nucleus, It consists of two layers (each about 75-100Aº thick) bounding a cisterna-like space, and the outer one being continuous with the endoplasmic reticulum. It is perforated by round holes (200-500Aº in diameter) called nuclear pores.
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Nuclear Plate - The aggregation of chromosomes in the equatorial plane during mitosis or meiosis.
Nuclear Reticulum - A meshwork of delicate threads of chroma tin which is seen in stained preparations of metabolic nuclei.
Nuclear Sap - The fluid lost by the chromosomes as they contract during prophase, and which fills the space of the nucleus.
Nucleoside. A chemical group which is consisting of a purine or pyrimidine base, and a pentose sugar.
Nucleosome (nubody) - Said of a nodule which is about 7-10 nm in diameter. It consists of histones around which a DNA strand, about 120 base pair long, is wrapped in the chromosomes. A type of histone, H1 is situated between adjacent nucleosomes and may lamp the DNA in position.
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Nuclear Spindle - Said of the fusiform structure, composed of fine fibrilos arranged longtudinal1y and converging at the poles, which appears in the cytoplasm of a cell surrounding the nucleus during mitosis and meiosis.
Nucleic Acids - The non-protein constituents of nucleo-proteins. They have a high molecular weight, and consist of alternate units of phosphate and a pentose sugar, which has a purine and pynmidine base attached to it.
Nucleohistone - Said of a complex of polynuc1eotides of DNA and histono proteins that are occurring only in nuclei of eukaryotic organisms and visible as nucleosmoes.
Nucleolar Organizer - Said of region of chromosomal DNA cod; g for ribosomal RNA and identified as secondary constric;tions (except centromere which is primary constriction) which are often located towards the end of chromosome.
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Nucleolus - A body, not having desoxyribose nucleotides and secreted by a specific organizer, gene or super-gene; in the resting nucleus.
Nucleoplasm - The ground-substance of the nucleus. It may appear granular or fibrils.
Nucleoprotein - A protein which is combined with, orcombinable with, a nucleic acid.
Nucleoside Diphoshate Sugars (NDP-sugars). Describing any of the compounds formed by reacting phosphorylated hexose sugar with a nucleoside triphosphate (NTP) by involving the general reaction: NIP + sugar I - phosphate = NDP -sugar + pyrophosphate.
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Nucleotide - Said of any base-phosphate complex having 3 essen; tial parts; a purine or pyrimidine base linked to carbon-1 of a pentose sugar (ribose or deoxyribose) which in turn gets esterified on carobon-5 tophosphoric acid. Polymers of nucleotides are known as polynucleotides which again are of two types; RNAP (containing ribose sugar and bases uracil, adenine, guanine and cytosine) and DNA (having deoxyri;bose sugar and bases adenine, guanine cytosine and thym;ine).
Nucleus - Said of cell organelle in eukaryotic cell which has ge;netic material (in chromatin)and nucleoplasm surrounded by a nuclear membrane.
Nullisomic - The zygote which is formed by fusion of gametes that both lack same chromosome and nullisomics are usually inviable.
Numerical Hybrid - A. hybrid whose parental gemetes are different in respect of the number of chromosomes.
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Numerical Mutation - A change in the number of chromosomes, either balaced to give polyploidy, or unbalanced to give aneuploidy.
Nurse Cell, Nurse Tissue. (1) Any cell or tissue in contact with developing gametes, and concerned with their nutrition. (2) In SclerodeJ71'lll, hyphae giving food material to spores which have become detached from the basidia.
Nut - A hard, dry usually one-seeded indehiscent fruit, which is derived from a syncarpous ovary.
Nutation - (1) The spiral growth of the apex of a plant organ e.g. shoots, tendrils, etc. It is caused by variation in the rate of growth of the meristematic areas. (2) The lateral swaying of the tip of a growing organ.
Nyctinasty - Describing a nastic movement where part (s), espe;cially leaf and flower take a characteristic position in-the night. These sleeping movements often cause folding together of leaflets.
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