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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >>Microheterogenity - Microtiter Agglutination Test
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β2-microglobulin (BMG)
A low molecular weight b-globulin containing a single polypeptide of 100 amino acid residues. It is synthesised by all nucleated cells and is found in all body fluids. It is present on the surface of mast cells. It is shed into circulation by lymphocytes and tumour cells. BMG is identical to the smaller subunit of the HLA-histocompatibility complex that regulates graft rejection. Plasma β2-microglobulin concentration is a reliable index of GFR because it is completely filtered by the glomeruli and is reabsorbed and catabolised by the cells of the PCT.
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Elevation in the levels of plasma BMG is seen in inflammatory conditions, renal failure and malignancy of the lymphoid system. BMG assay is useful in assessing graft rejection in recipients of kidney transplants.
Microgram
0.000001 or 10-6 grams.
Micrograph
A photograph of an image seen through a microscope. This may be a light micrograph or an electron micrograph.
Microheterogeneity
A slight variation in the nucleotide sequence of a DNA repeat unit. For example, the spacer regions in histone genes are copies of one another that differ lightly in the restriction fragment profiles.
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Microinjection
The introduction of small amounts of DNA or other compounds (RNA, enzymes, cytotoxic agents) into the nucleus or cytoplasm of a eukaryotic cell using finely constructed glass capillaries with the aid of a micromanipulator.
Microisolating system
Mechanical separation of single cells or protoplasts that allows them to proliferate individually.
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Micromanipulator
An instrument for guiding small instruments such as microinjection pipettes and icroelectrodes into target cells under a microscope.
Micron
A unit of distance: 10-6 m; 0.001 mm. Symbol: mm. Also termed micrometre.
2-micron circle
See 2-micron plasmid.
2-micron plasmid
A naturally occurring, double-stranded circular DNA plasmid containing 6318 base pairs present in 50 copies per cell in the yeast. It contains an origin of replication and can replicate autonomously. It is useful as a cloning vector. Also called 2μm circle, 2μ plasmid.
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Micronuclei
Small, spherical chromatin bodies found in the cytoplasm that resemble the main nucleus of a cell in shape, structure and staining properties. They are not incorporated into the nucleus during cell division. Micronuclei are formed from acentric chromosomes or chromatid-type fragments and whole chromosomes that have lagged behind during cell division and left out of both daughter nuclei. These are observable as small addition nuclei in interphase cells. Micronuclei are a reflection of clastogenic events and indicated the ongoing process of DNA damage.
Micronutrient
An essential nutrient that is normally required in concentrations less than 0.5 millimole/litre.
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Microorganism
An organism visible only under magnification.
Microparticle
Small particles of 0.1 to mm in size used to immobilise biological molecules or cells or to tag them. These are also referred to as Microspheres, microbeads or microcarriers. Microparticles include magnetic particles with ferrite iron core used in separations, nanoparticles of diameter less than 100 nm, and quantum particles or dots that are 10nm in size.
Micropipette
See Microelectrode.
Microplasts
Vesicles produced by subdivision and fragmentation of protoplasts or thin-walled cells.
Microporous gels
A chromatography matrix made up of cross-linked dextran or polyacrylamide. It is used to fractionate proteins.
Microprojectile bombardment
A method of gene transfer into plants that involves shooting DNA-coated metal (tungsten or gold) particles into them. See biolistics.
Micropropagation
The use of small pieces of tissue such as meristem grown in culture to generate large number of plants. It is a miniaturized in vitro multiplication and/or regeneration of plant material under aseptic and controlled environmental conditions. This is carried out on specially prepared media containing substances essential fro growth. Microprogation is used for three general types of tissue: excised embryos (embryo culture); shoot-tips (meristem culture or mericloning); and pieces of tissue that range from bits of stems to roots.
MicroRNA (miRNA)
A small RNA molecule of 21-23 nucleotides that forms an RNA-induced silencing complex (RISC) by associating with multiple proteins to repress translation of a specific target mRNA by hybridisation to its 3-untranslated region.
Microsatellite expansion
Expansion of microsatellite repeats which occurs in neurodegenerative disorders. A positive correlation is seen between expanded arrays of CG-rich trinucleotides and human neurological disorders. Fragile X, a common neurological disease, the first reported genetic disorder with microsatellite expansion is characterised by expansion of the trinucleotides repeat CGG in the 5untranslated region of the FMR1 gene resulting in hypermethylation and downregulation of gene expression.
Microsatellite instability
In stability of microsatellite sequences that occurs in a wide variety of cancers due to polymerases slippage associated with defects in DNA mismatch repair. The instability is not of equal intensity at every class of repeat; there may be a significant or only a minor change in repeat length and the size of the repeat may be longer or shorter than the original repeat. In extreme cases, the length of the repeats differs in different cells of the same
organism.
Microsatellites
Simple, short, non-coding, highly repetitive DNA sequences of 1-5bp in length repeated tens or hundreds of times at a stretch. They are widely distributed throughout the genome especially in multicellular organisms.
There are about 50,000-100,000 (dC-dA)n microsatellites interspersed in the human genome. Microsatellite repeats can be amplified by PCR and the products after gel electophoresis detected by radioactive or non-radioactive methods. Microsatellites exhibit a high degree of polymorphism. Variations in length are seen in a block of tandem repeats, between organisms of the same species and between cells of the same organism. Microsatellite polymorphisms have a major role in genomic analysis with applications in positional cloning, population genetic analysis, construction of human evolutionary trees, forensic sciences, medical diagnostics and tumor biology.
Microscopy
A method for the examination of biological systems to analyse the structure and chemistry.
Microsomes
Membrane residues formed from endoplasmic reticulum by fragmentation. These can be recovered by differential centrifugation.
Microspikes
Very thin actin-containing projections (0.1mm diameter × 5-10 mm length) that protrude out of the membrane of cultured animal cells.
Microtitre agglutination test
A Microscale test for the presence of an antibody or antigen based on the formation of a precipitate when an antigen and its corresponding antibody bind to each other. The test is carried out in a microtitre tray in which a fixed amount of antigen (or antibody) is added to wells containing dilutions of a sample of an unknown amount of the corresponding antigen (antibody). The results are semiquantitative.
Microtome
An instrument used for making this sections of biological specimens for microscopic analysis.
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