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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >> Heterologous Gene Expression - High Dose Dexamethasone Test
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Heterologous
From a different source. Describes gene sequences that show variable degrees of similarity although not identical.
Heterologous gene expression
The synthesis of foreign proteins in a host organism following transformation of that organism by a vector carrying genes from a different organism. However, this can pose a problem in bacterial hosts, which can degrade the heterologous proteins by proteases. Some heterologous proteins are deposited into insoluble inclusion bodies while others fail to fold properly. Furthermore, bacteria are incapable of adding sugar residues to proteins that require glycosylation.
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Heterologous protein
See recombinant protein.
Heteromultimeric proteins
Proteins containing nonidentical subunits encoded by different genes.
Heterophile antigen
A cross-reacting antigen that appears in widely ranging species such as humans and bacteria.
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Heteropolysaccharide
A polysaccharide that contains more than one type of sugar.
Heteropyknosis
The property of certain chromosomes, or of their parts, to remain more dense during the cell cycle and to stain more intensely than other chromosomes or parts.
Heterotrophic enzyme
An allosteric enzyme that requires a modulator other than its substrate.
Heterozygosity
The presence of different alleles at one or more loci on homologous chromosomes.
Heterozygote
An individual with different alleles at a specific locus on homologous chromosomes.
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Heuristic
In a computer programme, making guesses to obtain approximate results. This is however faster than searching.
Hexose monophosphate (HMP) shunt pathway
Also known as the pentose phosphate pathway. The major products of the pathway are ribose 5-phosphate and reduced nicotinamide adenine dinucleotide (NADPH). The pathway is active is adipose tissue, adrenal cortex and the mammary gland.
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Hidden Markov Model (HMM)
A joint statistical model for an ordered sequence of variables. The original variables are “hidden” as a result of stochastically perturbing the variables in Markov chain and the perturbed values can be continuous and are the “output” of the HMM. Hidden Markov models are used in bioinformatics because they allow a search or alignment algorithm to be trained using unaligned or unweighted input sequences. They also allow position-dependent scoring parameters such as gap penalties, thereby accurately modelling the consequences of evolutionary events on sequence families.
Hierarchical clustering
A data clustering method by which the most similar data points are clustered into a hierarchical tree.
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Heterosis
See hybrid vigour.
Heterotroph
An organism requiring preformed organic compounds for growth.
Heterozygous
The state of containing two different alleles of a particular gene such as the normal and an abnormal copy of the globin gene in individuals who are heterozygous for sickle cell anaemia.
Hfr
High – frequency recombination strain of Escherichia coli. In these strains, the F episome is integrated into the bacterial chromosome.
HGH
Human growth hormone.
Hexokinase
An enzyme that catalyses the Phosphorylation of glucose for entry into glycolysis.
Hexose
A sugar containing a six carbon backbone.
HGPRT
Hypoxanthine-guanine phosphoribosyltransferase. An enzyme that catalyses a major step in the formation of ATP and GTP from guanine. This pathway provides the means by which guanine and other purine analogs enter into nucleic acids.
HGPRT marker
The use of the HGPRT gene as a selectable marker. Cells that contain the mutant HGPRT gene are resistant to toxic purine derivatives.
HGSI (The Human Genome Sequencing Index)
A service provided by the NCBI to the International Consortium to support coordination and tracking of the Human Genome Project. The sequence data generated by the members are submitted via the HGSI website. The website presents the progress of the HGP to researchers.
Heteroplasmic
From ‘heterozygous cytoplasm’. An individual with organelles of different genotype.
Heteroplasmy
A condition in which two genetically different types of organelles are present.
Hheteroploid
Refers to a cell culture in which the cells comprising the culture possess nuclei containing chromosome numbers others than the diploid number.
Heteropolymer
A polymer composed of different types of monomer units. For example, proteins and nucleic acids.
High efficiency particulate air filter
See HEPA filter.
High endothelial venules (HEV)
Specialised cells that line capillaries in the lymphoid organs where leukocytes enter from the circulation.
High performance liquid chromatography (HPLC)
A chromatographic method conducted at high pressures using columns packed with tiny beads of matrix and automated equipment that enables highly reproducible profiles.
High threshold substances
Substances that are reabsorbed efficiently such as amino acids and glucose.
High-density lipoprotein (HDL)
A class of lipoproteins involved I the metabolism of chylomicrons and very low-density lipoproteins (VLDL) and in the transport of cholesterol from the cells to the liver. Two fractions of HDL-HDL2 and HDL3, can be separated by ultracentrifugation. HDL2 contains approximately 70 per cent lipid and 30 per cent protein, whereas, HDL3 is composed 45 per cent lipid and 55 per cent protein. Plasma HDL level is inversely related to the risk of coronary heart disease and is popularly known as ‘good cholesterol’.
High-dose dexamethasone test
A test for adrenal cortical function. A high dose of dexamethasone (8 mg) is used to suppress the insensitive feedback centre of pituitary disease. In cases where pituitary ACTH is already suppressed, as in adrenal cortical tumours and ectopic ACTH production, even the high dose will have no effect.
High – energy bond
A covalent bond which when hydrolysed, releases a large amount of free energy. A group that is linked to such a bond is transferred from one molecule to another readily. An example of a high-energy bond is the phosphodiester bond in ATP.
High – energy compound
A compound that undergoes hydrolysis with a large decreases in free energy under standard conditions.
Highly conserved sequence
DNA sequence that is very similar across several different types of organisms.
Highly repetitive DNA
DNA sequences present in 100 000 to 1000 000 copies per genome. These include the satellite, minisatellite and microsatellite sequences. The first component to reassociate after denaturation.
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