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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >>Localisome Long Accurate PCR LA PCR
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Liposome A small, artifical membrane vesicle composed of a spherical phospholipid bilayer that forms spontaneously when phospholipids are suspended in an aqueous buffer. Liposomes are used to transport drugs specifically into diseases cells thereby providing a means for drug targeting. They are also used to deliver DNA into the cell by entrapment of DNA, or bound to the surface of the vesicles, followed by subsequent fusion of the liposome with the cell membrane and release of DNA into the cell.
Lipotropic agent An agent (eg. choline, methionine)that prevents or reverses the development of fatty liver. Some lipotropic agents function as virus inactivating drugs.
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β-Lipotrophin See beta (β)-lipotrophin.
Liquefaction Enzymatic dig
estion of gelatinized starch to form lower molecular weight polysaccharides; generally catalysed by a-amylase.
Liquid (solution) hybridisation A reaction between complementary nucleic acid strands in solution.
Liquid media Media that lacks a solidifying agent.
Liquid nitrogen Nitrogen gas condensed to a liquid with a boiling point of about -196°C. It is useful as a medium for storing containers of genetic material. See cryopreservation.
Liquid scintillation counting A technique based on measurement of radiation from a source intimately in contact with the fluor, either dissolved or suspended in it.
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Lithotripsy A procedure for disintegrating stones into particles.
Litmus A pH indicator paper (range 4.5-8.3) that is impregnated with an extracted lichen pigment. It turns red in acidic and blue in alkaline solutions. However this is not a precies method of pH measurement.
Live vaccine A living, nonvirulent form of a microorganism or virus that is capable of eliciting an immune response. It protects the inoculated organism against infection by a virulent form of the microorganism or virus.
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Loading In chromatography, refers to introduction of a small volume on the stationary phase and allowing it to enter the column/gel.
Local alignment The alignment of certain regions rather than the complete length of two nucleic acid or amino acid sequences.
Local Area Network See LAN.
Local mediator Secreted signal molecule that functions at short range on adjacent cells.
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Local minima The nearest lower energy configuration of a molecule.
Localisome Refers to the presence of absence of proteins in particular cells or cellular compartments. In recent years large-scale determination of protein localization, localisome analysis, has been investigated in yeast and certain organelles in higher eukaryotic cells. This information augments the long accumulation of small-scale experiments which have determined the localization of various proteins under specific conditions. Together these findings have begun to reveal the complexity of protein localisation.
Locus (pl: loci) 1. A site on a chromosome. 2. The site at which a particular gene is located on a chromosome.
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Locus control region (LCR) A eukaryotic cis-acting element located at a considerable distance from the gene that it regulates. It is essential for transcriptional activity because it established an independent chromatin domain. It alleviates cis-repression caused by chromatin silencing and allows position-independent and copy number-dependent transgene expression.
Lod score The logarithm of the odds ratio designated as Z value. It is calculated from pedigree data, as the log (to base 10) of the ratio of the probability of the observed pedigree assuming linkage with a specified recombination fraction q, to the probability of the observed pedigree assuming no linkage, I.e., recombination fraction = 0.5 i.e. z= log10 {Prob(data|q)/Prob(data|0.5)}. It is used as a measure of genetic linkage and helps to determine whether cosegregation data support linkage between two genetic loci. While a Z value of +3.00 (1000:1) or greater favours linkage, a Z value of -2.00 (1:100) or less indicates that there is no linkage.
Logarithmic phase (exponential growth phase) The steepest slope of the growth curve; this is the phase in which rapid growth occurs and the cell number doubles every 20-30 minutes. See growth phases.
Lon (for long form of proteins) An ATP-dependent protease in bacteria that degrades defective proteins and proteins with short half-lives in a process that requires hydrolysis of two ATPs for each peptide bond cleaved.
Long accurate PCR (LA-PCR) A modification of the basic PCR that increases the efficiency of PCR and enables amplification of long template sequences. This is done by decreasing the reaction temperature, increasing the pH and using a combination of two DNA polymerases – Taq and Pfu. Using this technique, DNA fragments of up to 50 kb can be amplified. LA-PCR is useful for structural analysis of human genes, viral genomes such as HIV, and for the diagnosis of triplet nucleotide disorders such as Friedrich’s ataxia.
Long-acting thyroid stimulator (LATS) A serum factor with properties similar to TSH. LATS was found to be an immunoglobulin (lgG) that binds to TSH receptor in the plasma membrane of the thyroid gland and increase c-AMP by activating adenylate cyclase. It functions as a stimulatory autoantibody for the TSH receptor. This results in excessive production of T3 and T4 because LATS is not regulated by negative feedback, leading to diffuse enlargement of the thyroid. LATS is capable of crossing the placenta and causing neonatal hyperthyroidism even if the mother is euthyroid.
Long terminal repeat (LTR) A DNA sequence that is directly repeated at both ends of a retroviral genome. These are required for integration of the virus into the host genome.
Long branch attraction The positioning of groups of rapidly evolving sequences together in phylogenetic trees irrespective trees irrespective of their true relationships.
Long interspersed nuclear elements See LINEs.
Long-period interspersion A pattern in the genome in which long stretches of moderately repetitive DNA alternate with nonrepetitive DNA.
Long template A DNA strand synthesised during the polymerase chain reaction (PCR) that has a primer at one end but is extended beyond the site complementary to the second primer at the other end.
Long-term potentiation A long-lasting increase in the sensitivity of some synapses in the hippocampus which is induced by a short burst of repetitive firing in the presynaptic neurons.
Loop 1. A single-stranded region at the end of a hairpin in RNA or single-stranded DNA. This region corresponds to the sequence between inverted repeats in double-stranded DNA. 2. The section of a protein chain that connects classical secondary structures liked helix and sheet. This is of irregular structure, surface, exposed and containing hydrophilic residues. 3. A programming device that repeatedly executes a specific set of commands until a particular condition is reached.
Loop bioreactors Fermenters in which the fermenting material is cycled between a bulk tank and a smaller tank or loop of pipes. This aids in mixing the materials and ensuring uniform distribution of gas injected into the fermenter.
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- Dictionary of Bioinformatics, Biotechnology
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