deletion mutation A mutation in which one or more (sequential) nucleotides is lost from the genome. If the number lost is not divisible by three and is in a coding region, the result is a frame-shift mutation.
DELLA A family of nuclear growth repressors, first identified as gibberellin-signalling components, that restrain the growth of plants. Later shown to mediate effects of other phytohormones. There are five distinct DELLAs encoded in the Arabidopsis genome: GAI (gibberellin insensitive), RGA (repressor of ga1-3), RGL1 (RGA-like 1), RGL2 and RGL3. RGA and GAI are negative regulators of gibberellin signalling. Gibberellin stimulates growth via 26S proteasome-dependent destruction of DELLAs, thus relieving DELLA-mediated growth restraint. See GRAS family.
delphinidin The delphinidin gene codes for an enzyme closely related to the cyanidin gene and modifies the antho-cyanin dihydrokaempferol and directs pigment synthesis into the delphinidin pathway. Expression of this gene is responsible for the blue/violet colours of violas, delphiniums and grapes. Delphinidin, an active compound of red wine, inhibits endothelial cell apoptosis via the nitric oxide pathway and regulation of calcium homeostasis.
Delta Dl Neurogenic gene locus in Drosophila. Gene product contains nine repeats of the EGF-like domain and is one of the ligands for Notch.
delta chains S-chains See immunoglobulin. The heavy chains of mouse and human IgD immunoglobulins.
delta sleep-inducing peptide dsip a natural somno-genic peptide found in neurons, peripheral organs and plasma; induces mainly delta sleep in mammals. There are nine amino acid residues (Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu). DSIP has effects in pain, adaptation to stress and epilepsy; it also has anti-ischemic effects.
delta virus Hepatitis D virus. A defective RNA virus requiring a helper virus, usually hepatitis B virus, for replication. Delta virus infections may exacerbate the clinical effects of hepatitis B.
delta-endotoxin S-endotoxin The toxic glycoprotein produced by sporulating Bacillus thuringiensis that can kill insects.
dematin Band 4.9 Actin microfilament-bundling protein (52 kDa, but variants of similar molecular weight are reported); contains an SH3 domain and is extensively palmitoylated; associated with membrane of erythrocytes
(protein 4.9). A substrate for PKC and PKA and bundling of actin is regulated by PKA-mediated phosphorylation.
demissine Toxic glycoalkaloid from Solanum spp. See chaconine, solanine, potato glycoalkaloids.
demyelinating diseases Diseases in which the myelin sheath of nerves is destroyed and that often have an autoimmune component. Examples are multiple sclerosis, acute disseminated encephalomyelitis (a complication of acute viral infection), experimental allergic encephalomyelitis, Guillain-Barré syndrome.
denaturation Reversible or irreversible loss of function in proteins and nucleic acids resulting from loss of higherorder (secondary, tertiary or quaternary) structure produced by non-physiological conditions of pH, temperature, salt or organic solvents.
dendrite A long, branching outgrowth from a neuron, that carries electrical signals from synapses to the cell body - unlike an axon, which carries electrical signals away from the cell body. This classical definition, however, lost some weight with the discovery of axo-axonal and dendro-dendritic synapses.
dendritic cells 1. Follicular dendritic cells, found in germinal centres of spleen and lymph nodes; retain antigen for long periods. 2. Accessory (antigen-presenting) cells, positive for class II histocompatibility antigens, found in the red and white pulp of the spleen and lymph node cortex and associated with stimulating T-cell proliferation.
3. T-lymphocyte found in epidermis and other epithelial cells involved in antigen recognition expressing predominantly ^8-TCR receptors (dendritic epidermal cells: DECs).
4. DOPA-positive cells derived from neural crest and found in the basal part of epidermis: melanocytes distinct from (3). See also Langerhans cells.
dendritic spines Wineglass- or mushroom-shaped protrusions from dendrites that represent the principal site of termination of excitatory afferent neurons on interneurons, especially in the cortical regions.
dendritic tree Characteristic (tree-like) pattern of outgrowths of neuronal dendrites.
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