Acetycholine – Neurotransmitter released at the neuromuscular junction.
Adenine – One of the four bases found in DNA, having the double-ring structure of a class known as purines. Adenine always forms complementary base paring with a DNA pyrimidine base called thymine. When pairing with RNA duringtranscription, adenine is complementary to uracil. Adenine also occurs in RNA molecules.
ALS – A serious neurological disease that results from the progressive degeneration of the motor neurons.
alpha-actinin – A protein (of size 100 kD) normally found as a dimer and that may link actin filaments end-to-end with opposite polarity. Originally described in the Z-disc, now known to occur in stress-fibres and at focal adhesions.
amino acid – Compound that forms the basic structural units of all proteins. Each amino acid molecule contains acidic carboxyl and nitrogeneous amino groups of atoms linked to a variable ring or chain of carbon atoms.
Apoptosis – Process of cell death that results from turning on specific, active processes in the cell that lead the cell to kill itself. This happens normally in some tissues, for example, during embryonic development when some groups of cells are removed from the animal. In these apoptotic cells during development, genes are turned on as part of the developmental process that cause the cell to kill itself. In other non-developmental cases of apoptosis, factors from outside the cell can cause the target cell to turn on apoptosis leading to its own death. A way for a lay-person to view apoptosis is as a form of cell suicide.
Autosome – Any of the chromosomes that are NOT involved with sex determination.
basement membrane – Extracellular matrix characteristically found under epithelial cells. There are two distinct layers: the basal lamina, immediately adjacent to the cells, is a product of the epithelial cells themselves and contains collagen type IV, and the reticular lamina is produced by fibroblasts of the underlying connective tissue and contains fibrillar collagen.
Chromosome – Chromosomes are found in the cell nucleus and consist of long chains of nucleic acids coated withprotein. Each cell contains 46 chromosomes – 23 from the mother and 23 from the father. The cell’s DNA is subdivided into chromosomes, possibly for convenience of handling, each of which has a long length of DNA associated with various proteins. Each chromosome has a characteristic length and banding pattern.
cytoskeletal protein – Major constituent of the cytoskeleton found in the cytoplasm. They form a flexible framework for the cell, provide attachment points for organelles and formed bodies, and make communication between parts of the cell possible.
Cytosine – One of the four types of nitrogenous bases found in DNA, having the single-ring structure of a class known as pyrimidines. Cytosine always forms complementary base pairing with a DNA purine base called Guanine. Cytosine also occurs in RNA molecules.
deletion mutation – A mutation in which one or more (sequential) nucleotides is lost by the genome. If the number lost is not divisible by 3 and is in a coding region, the result is a frameshift mutation.
deoxyribonucleic acid (DNA) – Primary genetic material of all cells. DNA molecules are a long, chain-like strings of polysugar and phosphate chemical groups. DNA, which holds the coded genetic instructions and regulates enzymeproduction, usually consist of two intertwined chains. The chain resembles a ladder twisted into a double helix, spiral shape.
Diaphragm – The musculomembranous partition separating the abdominal and thoracic cavities, and serving as a major inspiratory muscle.
Duchenne Muscular Dystrophy (DMD) – An x-linked hereditary disease characterized by the absence of a proteinknown as dystrophin which causes degeneration and necrosis of skeletal muscle fibres. The incidence of this disorder is about 1 in 3500 male births and of these a third are estimated to be new mutational events.
dystroglycan (156DAG, 43DAG, A3a) – Complex composed of two proteins, alpha and beta-dystroglycans (formerly known as 156DAG and 43DAG / A3a respectively). Dystroglycan is a transmembrane protein that associates withdystrophin in the cytoplasm and alpha-dystroglycan, an extracellular glycoprotein, on the exterior face. Alpha-dystroglycan binds to dystrophin, thus linking actin through dystrophin and beta-dystroglycan to the extracellular matrix. Also associates with dystrophin. Dystrophin deficiency leads to a deficiency in the appearance of these proteins on thesarcolemma, even though they are not themselves defective.
Dystrophin – Large protein found on the inner side of the membrane surrounding each muscle fiber. Its purpose seems to be to maintain shape and structure of the muscle fiber similar to the way joists, rafters and posts keep a house standing. Mutations in the DMD gene result in dystrophin deficiency which constitutes the pathogenic basis of DMD.
Enzyme – A protein that acts as a catalyst, speeding the rate at which a biochemical reaction proceeds but not altering the direction or nature of the reaction.
Eukaryote – Cell or organism with membrane-bound, structurally discrete nucleus and other well-developed subcellular compartments. Eukaryotes include all organisms except viruses, bacteria, and blue-green algae. See prokaryote.
Exon – Protein coding sequences of the primary RNA transcript (or the DNA that encodes them). It exits the nucleus as part of a messenger RNA molecule. In the primary transcript neighboring exons are separated by introns.
frame-shift mutation – Insertion or deletion of a number of bases not divisible by three in an open reading frame in aDNA sequence. Such mutations usually result in the generation, downstream, of nonsense, chain-termination codons.
Gene – Originally defined as the physical unit of heredity but the meaning has changed with increasing knowledge. It is probably best defined as the unit of inheritance that occupies a specific locus on a chromosome, the existence of which can be confirmed by the occurrence of different allelic forms. Given the occurrence of split genes, it might be re-defined as the set of DNA sequences (exons) that are required to produce a single polypeptide.
gene transfer – The introduction of functional (usually cloned) genes into cells and organisms. A variety of techniques can be used for gene transfer: (1) cell hybridization; (2) microcell-mediated gene transfer; (3) chromosome-mediated gene transfer; (4) DNA-mediated gene transfer. Gene transfer results in genetically transformed cells and individuals and is a step in recombinant DNA technology when cloned genes are being used for transfer.
Glutamate – A neurotransmitter that is normally involved in learning and memory. It appears to cause the death of nerve cells in a variety of neurodegenerative disorders.
Glycoprotein – Proteins with covalently attached sugar units, either bonded via the OH group of serine or threonine (O-glycosylated) or through the amide NH2 of asparagine (N-glycosylated). Includes most secreted proteins (serum albumin is the major exception) and proteins exposed at the outer surface of the plasma membrane. Sugar residues found include:- mannose, N-acetyl glucosamine, N-acetyl galactosamine, galactose, fucose and sialic acid.
Guanine – One of the four types of nitrogenous bases found in DNA, having the double-ring structure of a class known as purines. Guanine always forms complementary base pairing with a DNA pyrimidine base called cytosine. Guanine also occurs in RNA molecules.
Heterologous – Derived from the tissues or DNA of a different species.
immunosuppressive agents – Agents that suppress immune function by one of several mechanisms of action. Classical cytotoxic immunosuppressants act by inhibiting DNA synthesis. Others may act through activation of suppressor T-cell populations or by inhibiting the activation of helper cells. While immunosuppression has been brought about in the past primarily to prevent rejection of transplanted organs, new applications involving mediation of the effects of interleukins and other cytokines are emerging.
messenger RNA (mRNA) – Negative copy (single-stranded RNA molecule) of a gene which is used to decode the original gene by specifying the amino acid sequence of one or more polypeptide chains. The messenger RNA passes out of the nucleus and into the cytoplasm where it is latched on to by decoding particles called ribosomes.
Muscle – Muscle is a tissue composed of bundles of cells that have the ability to contract and relax to create movement. These cells create mechanical energy from chemical reactions. Muscles serve many functions. They produce movements of the body. They are used to maintain position of the body against gravity. They also can be used to alter pressures or tensions of structures within the body as well as protect the body. The three types or classifications of muscle are striated (skeletal), smooth and cardiac. Striated muscles attach to the skeleton. Smooth muscle is the type such as found in the stomach and blood vessels. Cardiac muscle forms the walls of the heart.
Muscular Dystrophy (MD) – refers to a group of genetic myopathies in which a muscle protein is absent, deficient or abnormal. Muscular dystrophies are myopathies in which a genetic defect results in structural damage to the muscle. Other myopothies involve damage to the muscle¹s contraction apparatus or energy production system. The three main types are pseudohypertrophic (Duchenne, Becker), limb-girdle, and facioscapulohumeral.
Myasthenia – Muscle weakness or lack of strength. Today, ³myasthenia² refers specifically to muscle weakness resulting from fault communication between nerve and muscle at the place where nerve and muscle meet (the neuromuscular junction).
Myoblast – Cell that by fusion with other myoblasts gives rise to myotubes that eventually develop into skeletal musclefibres. The term is sometimes used for all the cells recognizable as immediate precursors of skeletal muscle fibres. Alternatively, the term is reserved for those post-mitotic cells capable of fusion, others being referred to as presumptive myoblasts.
Myofibril – Long cylindrical organelle of striated muscle, composed of regular arrays of thick and thin filaments, and constituting the contractile apparatus.
Myotube – Elongated multinucleate cells (three or more nuclei) that contain some peripherally located myofibrils. They are formed in vivo or in vitro by the fusion of myoblasts and eventually develop into mature muscle fibres that have peripherally located nuclei and most of their cytoplasm filled with myofibrils. In fact, there is no very clear distinction between myotubes and muscle fibers proper.
Nebulin – Family of large matrix proteins (600 – 900 kD) found in the N-line of the sarcomere of striated muscle. Consist of many (more than 200) repeats of conserved actin-binding motifs; bind to F-actin and may serve as templates for assembly of the sarcomere.
Necrosis – Process of cell death that results from massive disruption of normal cellular homeostasis, that is so disruptive that the cells cannot repair themselves and then die. This is a common form of cell death following injury to tissue.
Neuropathy – any disease of the nervous system. Amyotrophic lateral sclerosis and spinal muscular atrophy, in which loss of nerve cells prevents muscles from working, are neuropathies, as are diseases in which nerve fibers malfunction, such as Charcot-Marie-Tooth and Dejerine-Scottas disease.
Neurotransmitter – A chemical that is released from one neuron and attaches to an adjacent neuron triggering a nerve impulse.
open reading frame – A reading frame in a sequence of nucleotides in DNA that contains no termination codons and so can potentially translate as a polypeptide chain. primary transcript RNA transcript immediately after transcription in the nucleus, before RNA splicing or polyadenylation to form the mature mRNA.
Peptide – Macromolecule consisting of several amino acids linked via amide bonds between their COOH and NH2 groups. Peptides do not necessarily adopt a defined spatial structure (in contrast to proteins), but the difference is blurred.
Phenotype – The outward appearance of the individual. It is the product of interactions between genes and between the genotype and the environment.
polymerase chain reaction (PCR) – Method for producing large amounts of specific DNA or RNA fragments of defined length and sequence from small amounts of short oligonucleotide flanking sequences (primers). The reaction is efficient, specific, and extremely sensitive. Uses for the reaction include disease diagnosis, detection of difficult-to-isolate pathogens, mutation analysis, genetic testing, DNA sequencing, and analyzing evolutionary relationships.
Primer – Short pre-existing polynucleotide chain to which new deoxyribonucleotides can be added by DNA polymerase.
Prokaryote – Cell or organism lacking a membrane-bound, structurally discrete nucleus and other subcellular compartments. Bacteria are prokaryotes. See eukaryote.
reading frame – One of the three possible ways of reading a nucleotide sequence. As the genetic code is read in non-overlapping triplets (codons) there are three possible ways of translating a sequence of nucleotides into a protein, each with a different starting point. For example, given the nucleotide sequence: AGCAGCAGC, the three reading frames are: AGC AGC AGC, GCA GCA, CAG CAG.
restriction map – Map of DNA showing the position of sites recognized and cut by various restriction endonucleases.
revertant (flat revertant) – Variant of a malignant-transformed animal tissue cell in which the characteristic high saturation density and piled-up morphology have reverted to the flatter morphology associated with non-transformed cells.
ribonucleic acid (RNA) – This molecular species has an informational role, a structural role and an enzymic role and is used in a more versatile way than either DNA or proteins. Considered by many to be the earliest macromolecule of living systems. The structure is of ribose units joined in the 3′ and 5′ positions through a phosphodiester linkage with apurine or pyrimidine base attached to the 1′ position. All RNA species are synthesised by transcription of DNA sequences, but may involve post-transcriptional modification.
Sarcomere – Repeating subunit from which the myofibrils of striated muscle are built. Has A and I bands, the I band being sub-divided by the Z-disc, and the A-band being split by the M-line and the H-zone.
Sarcolemma – Plasma membrane of a striated muscle fiber.
sarcoplasmic reticulum – Endoplasmic reticulum of striated muscle, specialized for the sequestration of calcium ions that are released upon receipt of a signal relayed by the T-tubules from the neuromuscular junction.
skeletal muscle – A rather non-specific term usually applied to the striated muscle of vertebrates that is under voluntary control. The muscle fibres are syncytial and contain myofibrils, tandem arrays of sarcomeres.
Spectrin – Membrane-associated dimeric protein of erythrocytes. Forms a complex with ankyrin, actin, and probably other components of the ‘membrane cytoskeleton’, so that there is a meshwork of proteins underlying the plasma membrane, potentially restricting the lateral mobility of integral proteins. Contains the EF-hand motif.
striated muscle – Muscle in which the repeating units (sarcomeres) of the contractile myofibrils are arranged in registry throughout the cell, resulting in transverse or oblique striations observable at the level of the light microscope, eg. the voluntary (skeletal) and cardiac muscle of vertebrates.
Transfection – The introduction of DNA into a recipient cell and its subsequent integration into the recipient cell’s chromosomal DNA.
Translocation – A type of aberration characterized by fragmentation of a chromosome and transfer of the broken-off portion to another chromosome, often of a different pair.
Thymine – A nitrogen-containing, single-ring, basic pyrimidine that occurs in nucleotides of DNA and RNA. The other pyrimidine in DNA is cytosine, and in RNA is uracil. Thymine is one member of the base pair A-T (adenine-thymine).
utrophin (dystrophin associated protein) – Autosomal homologue of dystrophin (of size 395kD) localized near the neuromuscular junction in adult muscle, though in the absence of dystrophin (i.e. in Duchenne muscular dystrophy) utrophin is also located on the cytoplasmic face of the sarcolemma.
Virus – A noncellular biological entity that can reproduce only within a host cell. Viruses consist of nucleic acid covered by protein; some animal viruses are also surrounded by membrane. Inside the infected cell, the virus uses the synthetic capability of the host to produce progeny virus.