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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >>K Homology Domain Khorana Har Gobind

K1. See equilibrium constant. 2. A statistical parameter used in calculating BLAST scores. It is a natural scale for search space size and converts a raw score to a bit score.

K-homology domain An RNA-binding motif in proteins. This was first identified in the heterogeneous nuclear RNA biding protein hnRNPK. This protein contains three copies of the domain. This motif has also been identified in other RNA-binding proteins such as the product of the fragile X-gene FMR1. This domain contains a three-strand β sheet and 3 α-helices with the topology β-α-α-β-βα. Specific interactions are believed to occur between RNA and residues present in the linker between the first two α-helices.

K-ras The oncogene carried by the Kristen sarcoma virus. K-ras is a member of the ras gene family.

K+ leak channel A K+-transporting ion channel present in the plasma membrane of animal cells that remains open even in the resting state.

Ka See affinity constant.

Kallidin See kinins.

Kallikreins Serine proteases that are components of the intrinsic pathway of blood coagulation.

Kallman syndrome A hypothalamic disorder characterised by hypogonadotrophic hypogonadism, which may be due to defective GnRH production or release, associated with sexual immaturity and eunchoid habitus. Congenital isolated gonadotrophin deficiency occurs in postmenopausal women and in men with primary hypogonadism. The levels of LH and FSH are reduced. The syndrome may be due to an X-linked mutation and presents with skeletal defects, mental retardation, Cryptorchidism and anosmia (lacking the sense of smell).

Kanamycin An antibiotic of the aminoglycoside family that inhibits translation by biding to the ribosome.

Kanr Kanamycin-resistance gene. See selectable marker.

Kappa chain One of two types of antibody light chains. See lambda chain.

Karyogamy The fusion of nuclei or nuclear material during sexual reproduction. See fertilization.

Karyogram A picture or ideogram of stained chromosome arranged in homologous pairs used to identify chromosomes aberrations.

Karyokinesis The division of a cell nucleus. See meiosis; mitosis.

Karyopherin A member of the family of nuclear transport proteins that functions as an importin, exportin or both.

Karyoplast The cell fraction that contains the nucleus surrounded by a ring of cytoplasm in cells enucleated by cytochalasin.

Karyotype 1. The chromosome constitution of a cell, an individual or of a related group of individuals ass visualised at mitosis. It is defined both by the number an the morphology of the chromosomes. Mitotic metaphase chromosomes are arranged in order of length and according to position of the centromere. 2. Abbreviated formula for the chromosome constitution, such as 47, XX + 21 for human Trisomy-21 (Down syndrome).

Kayser-Fleischer rings Deposition of copper in the Descements membrane of the cornea in some patients with Wilsons disease who exhibit neuropsychiatric signs.

Kb Kilobase pairs. See base pair; kilobase.

Kcat The catalytic rate constant characteristic for an enzyme-catalysed reaction. Higher the value of kcat, greater is the conversion of substrate into product.

Kcat/Km The catalytic efficiency of an enzyme-catalysed reaction. Larger the value of kcat/Km, greater is the speed and efficiency of conversion of the substrate into product.

K cell An effector lymphocyte with Fc receptors that allow it to bind to and kill antibody-coated target cells.

KEGG Kyoto Encyclopaedia of Genes and Genomes. A very comprehensive Japanese online resource for information on metabolic pathways.

Kelley Seegmiller syndrome A syndrome caused by partial deficiency of hypoxanthine guanine Phosphoribosyl transferase (HGPRT) characterised by gout and renalcalculi.

Kennedys disease An X-linked neurological disorder with an expansion of the trinucleotide CAG. This affects the androgen receptor resulting in decreased activation of androgen-responsive genes.

Keratinocyte A mammalian epithelial cell.

Keratins Insoluble structural proteins that consist of parallel polypeptide chains in α-helical of β-conformations. They serve protective functions in the cell.

Keratitis Inflammation of the cornea.

Keratomalacia UIceration and necrosis of the cornea resulting from sever vitamin A deficiency.

Kernicterus Severe neurological symptoms associated with hyperbilirubinaemia.

Keshan disease Selenium deficiency endemic in Keshan province in China where the soil has low selenium content. The clinical symptoms include myopathy, cardiac enlargement and arrhythmias.

Ketogenesis The formation of ketone bodies from acetyl CoA in the liver.

Ketogenic amino acids Amino acids that are converted to acetyl CoA and other molecules that cannot be used to synthesise glucose or TCA cycle intermediates.

Ketonaemia High levels of ketone bodies in the blood.

Ketone A functional group in an organic compound in which a carbon atom is linked to an oxygen by a double bond. Neither of the other substituents attached to the carbon is a hydrogen.

Ketone bodies Acetoacetate, β-hydroxybutyrate and acetone. These are synthesised from acetyl CoA in the liver and used as fuel by extrahepatic tissues such as the heart and kidney.

Ketonuria High concentration of ketone bodies in the urine. This is seen during starvation and in uncontrolled diabetes mellitus.

Ketose A monosaccharide in which the carbonyl group is a ketone.

Ketosis The presence of excessive amount of ketone bodies in body tissues and fluids. Ketosis is seen in starvation and uncontrolled diabetes mellitus.

Khorana, Har Gobind (b. 1922) A biochemist who was awarded the Nobel Prize in Medicine in 1968 for his contribution in cracking the genetic code. He used synthetic oligoribonucleotides to programme the synthesis of peptides. He was also responsible for isolating DNA ligase.

Kidney stones See renal calculi.

Killed vaccine A vaccine composed of killed pathogen.

Killer factor Linear, double stranded plasmids that confer a killer phenotype on the host. These are found in yeast.
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