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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >> Insulin Hypoglycaemia Test - Integration
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Insertional RNA editing
A cotranscriptional process that involves insertion of single nucleotides or small runs of nucleotides such as G insertions during transcription of the paramyxovirus P gene.
Insulator element
A DNA sequence that prevents a regulatory protein bound to the control region of one gene from influencing the transcription of a adjacent genes.
Insulin
The first protein demonstrated to have hormone action and synthesised as a large precursor molecule. It is also the first protein to be crystallised, sequenced, chemically synthesised and commercially prepared by recombinant DNA technology.
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The association between insulin deficiency and diabetes was established by Banting and Best in 1921. Insulin is a heterodimeric polypeptide-the A and B chains contain 21 and 30 amino acids respectively containing one intrachain and two interchain disulphide bridges. Insulin is synthesised in the β cells of the pancreatic islets as a preprohormone, which is processed to form proinsulin. Proinsulin undergoes proteolysis to generate equimolar amounts of mature insulin and C-peptide. Insulin enhances carrier-mediated facilitated diffusion of glucose, galactose, xylose and arabinose in adipose tissue cells. The hormone also promotes the entry of amino acids, potassium, calcium, phosphate and nucleotides. Insulin increases glucose utilisation by enhancing hepatic glycolysis and decreasing glucose release into circulation. It promotes glycogen synthesis in the liver and muscle by increasing the activities of glucokinase, hexokinase II and glucogen synthase. The hormone inhibits glycogenolysis and Gluconeogenesis. Insulin has an anabolic effect on fat and protein metabolism. It has stimulatory effects on cell replication in vitro and growth in vivo. Insulin binds to a glycoprotein receptor on the plasma membrane of target cells. The receptor undergoes autophosphorylation and in turn phosphorlates IRS-1 that binds to GTPases, protein kinases and lipid kinases mediating the metabolic actions of insulin. Insulin deficiency causes diabetes mellitus.
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Insulin autoimmunity
Autoimmunity that arises due to antibodies to insulin or insulin receptors. Antibodies to endogenous insulin cause inappropriate dissociation of insulin from hormone-antibody complex or release excessive insulin from the pancreas. Antibodies against insulin receptors can cause insulin resistance and hypoglycaemia.
Insulin hypoglycaemia test
A test for investigating pituitary function. Insulin, 0.1-0.2 U/kg body weight is given intravenously after an overnight fast. Blood samples are withdrawn for the estimation of glucose and cortisol before the injection and 15, 30, 60, 90 and 120 minutes after injection. Plasma cortisol concentration increases in response to insulin-induced hypoglycaemia in normal subjects, whereas patients with Cushing’s syndrome fail to show a rise.
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Insulin receptor
A glycoprotein present on the plasma membrane of target cells. The functional insulin receptor is a heterodimer (α2β2) with the two subunits linked by disulphide bonds. The α-subunit is extracellular and responsible for binding insulin via a cysteine-rich domain. The β-subunit is a transmembrane protein with tyrosine kinase activity and an autophosphorylation site, both of which are involved in signal transduction and insulin action. Binding of insulin to the receptor brings about a conformational change in the receptor. The receptors cross-link, form aggregates and are internalized. The receptor undergoes autophosphorylation and in turn phosphorylates insulin receptor substrate 1 (IRS-1) on tyrosine residues. Phosphorylated IRS-1 binds to the SH2 domains of proteins such as GTPases, protein kinases and lipid kinases that mediate the metabolic actions of insulin.
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Insulin suppression test
A test for the differential diagnosis of hypoglycaemia. Following an overnight fast, an indwelling intravenous cannula is inserted and kept patent with sodium citrate solution or heparinised saline. Fasting blood sample is collected for estimation of plasma glucose and C-peptide. Insulin (0.15 U/kg body weight) is injected intravenously followed by collection of blood samples every half an hour for 21/2 hours. In normal subjects, the plasma C-peptide concentrations are less than 50 per cent of the initial value. A failure of plasma C-peptide to fall confirms the diagnosis of insulinoma.
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Insulin test
A test for gastric function. Insulin by inducing hypoglycaemia, stimulates the vagus causing gastric acid secretion. Insulin test is used to assess the success of vagotomy, which is done as a treatment for patients with duodenal ulcer. After an overnight fast, four 15-minute specimens are collected. Insulin, 0.23 units/kg body weight is given intravenouslay and eight 15-minute samples are aspirated every 15 minutes for 2 h. Blood glucose concentration is determined before insulin administration, as well as 30 and 45 minutes after insulin injection. Inpatients before vagal resection, there is a significant and prolonged elevation in gastric acid secretion (>100 mmol/L). Following vagotomy, the increase in acid secretion is less than 20 mmol/L above the basal levels.
Insulin-dependent diabetes mellitus (IDDM)
See diabetes mellitus type I.
Insulin-like growth factor (IGF.)
A polypeptide hormone whose synthesis is stimulated by growth hormone.
Insulinomas
Insulin-secreting primary tumours of the β-cells of the pancreatic islets. The plasma insulin levels are high despite low fasting plasma glucose levels.
Int1 gene
An oncogene activated by adjacent integration of the mouse mammary tumour virus (MMTV) that induces mammary tumours in mice. The int1 gene homologue in Drosophila melanogaster plays an important role in wing development.
Intasome
A complex formed between bacteriophage DNA and two proteins (Int and IHF) required for bacteriophage DNA integration into the bacterial host DNA when the phage enters the lysogenic pathway.
Integral membrance protein
A protein inserted into a membrane. It associates with the membrane by means of ~25 amino acids that are uncharged and/or hydrophobic.
Integrant
A cell in which the transfected gene has become stably integrated into the genome of the recipient.
Integrase
An enzyme that catalyses site-specific recombination of lambda DNA with bacterial DNA resulting integration of the phage into the host.
λ-integrase family
See λ-integrase family.
Integration
1. Insertion of a small DNA molecule into the chromosomal DNA. This is generally brought about by homologous recombination. For circular molecules, integration involves only a single crossing-over, whereas for linear molecules two crossings-over are required. A classic examples is the integration of phage λ (lambda) DNA into the E. coli genome. 2. In statistics, the revedrse process of differentiation. 3. An analysis that involves that involves the combined use of two or more large datasets. This allows researchers to increase the value obtained from the data, because it increases the base of information that can be accessed and allows for more robust searching.
Integration-excision (I/E) region
The portion of bacteriophage λ DNA to be inserted into a specific site in the E.coli chromosome and excised from this site.
Integration host factor (IHF)
A protein that mediates site-specific recombination between sequences termed attachment (att) sites.
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