A while back someone asked about a Glossary of Terms it was a slow response but I finally got one together. This is a first pass and I am sure I will be adding to it. You can use your Browser to "FIND" a term or the Search Function. ABC transporter proteins- Large superfamily of membrane transport proteins that use the energy of hydrolysis of ATP to transfer peptides and a variety of small molecules across membranes. abduction- Lateral movement away from the midline of the body. acetyl- Chemical group derived from acetic acid. Acetyl groups are important in metabolism and are added covalently to some proteins as a posttranslational modification. acetyl CoA- Small water-soluble molecule that carries acetyl groups in cells. It consists of an acetyl group linked to coenzyme A (CoA) by an easily hydrolyzable thioester bond. acetylcholine receptor-Ion channel that opens in response to binding of acetylcholine, thereby converting a chemical signal into an electrical one. Best understood example of a transmitter-gated channel. Sometimes called the nicotinic acetylcholine receptor to distinguish it from a muscarinic acetylcholine receptor, which is a G-protein-linked cell-surface receptor. acetylcholine- Neurotransmitter that functions at a class of chemical synapses known as cholinergic synapses. Found both in the brain and in the peripheral nervous system. It is the neurotransmitter at vertebrate neuromuscular junctions. actin- Abundant protein that forms actin filaments in all eucaryotic cells. The monomeric form is sometimes called globular or G-actin; the polymeric form is filamentous or F-actin. actin-binding protein- Protein that associates with either actin monomers or actin filaments in cells and modifies their properties. Examples include myosin, a-actinin, and profilin. actin filament (microfilament)- Helical protein filament formed by the polymerization of globular actin molecules. A major constituent of the cytoskeleton of all eucaryotic cells and part of the contractile apparatus of skeletal muscle. action potential- Rapid, transient, self-propagating electrical excitation in the plasma membrane of a cell such as a neuron or muscle cell. Action potentials, or nerve impulses, make possible long-distance signaling in the nervous system. active site- Region of an enzyme surface to which a substrate molecule binds in order to undergo a catalyzed reaction. active transport- Movement of a molecule across a membrane or other barrier driven by energy other than that stored in the electrochemical gradient of the transported molecule. acyl group- Functional group derived from a carboxylic acid ( ). (R represents an alkyl group, such as methyl.) adaptation- Adjustment of sensitivity following repeated stimulation. This is the mechanism that allows a neuron, a photodetector, or a bacterium to react to small changes in stimuli even against a high background level of stimulation. adaptor protein- General term for proteins in intracellular signaling pathways that link different proteins in the pathway directly together. Adduction- Medial movement toward the midline of the body. adenosine triphosphate see ATP adenylyl cyclase (adenylate cyclase)- Membrane-bound enzyme that catalyzes the formation of cyclic AMP from ATP. An important component of some intracellular signaling pathways. adherens junction- Cell junction in which the cytoplasmic face of the plasma membrane is attached to actin filaments. Examples include the adhesion belts linking adjacent epithelial cells and the focal contacts on the lower surface of cultured fibroblasts. adhesion plaque- see focal adhesion. adipocyte- A fat cell. ADP (adenosine 5-diphosphate)- Nucleotide that is produced by hydrolysis of the terminal phosphate of ATP. It regenerates ATP when phosphorylated by an energy-generating process such as oxidative phosphorylation. adrenaline (epinephrine)- Hormone released by chromaffin cells (in the adrenal gland) and by some neurons in response to stress. Produces "fight or flight" responses, including increased heart rate and blood sugar levels. aerobic- Describes a process that requires, or occurs in the presence of, gaseous oxygen (O2). affinity constant (association constant) (Ka)- Measure of the strength of binding of the components in a complex. For components A and B and a binding equilibrium A + B AB, the association constant is given by [AB]/[A], and is larger the tighter the binding between A and B. (See also dissociation constant.) Agonist- A muscle that causes motion. Akt- see protein kinase B alcohol- Polar organic molecule that contains a functional hydroxyl group (OH) bound to a carbon atom that is not in an aromatic ring. An example is ethyl alcohol (CH3CH2OH). alkaloid- Small but chemically complex nitrogen-containing metabolite produced by plants as a defense against herbivores. Examples include caffeine, morphine, and colchicine. alkyl group- General term for a group of covalently linked carbon and hydrogen atoms such as methyl (CH3) or ethyl (CH2CH3) groups. These groups can be formed by removing a hydrogen atom from an alkane. allele- One of a set of alternative forms of a gene. In a diploid cell each gene will have two alleles, each occupying the same position (locus) on homologous chromosomes. alternative RNA splicing- The production of different proteins from the same RNA transcript by splicing it in different ways. amino acid- Organic molecule containing both an amino group and a carboxyl group. Those that serve as the building blocks of proteins are alpha amino acids, having both the amino and carboxyl groups linked to the same carbon atom. aminoacyl-tRNA synthetase- Enzyme that attaches the correct amino acid to a tRNA molecule to form an aminoacyl-tRNA. aminoacyl tRNA- Activated form of amino acid used in protein synthesis. Consists of an amino acid linked through a labile ester bond from its carboxyl group to a hydroxyl group on tRNA. AMP (adenosine 5-monophosphate)- One of the four nucleotides in an RNA molecule. Two phosphates are added to AMP to form ATP. amphipathic- Having both hydrophobic and hydrophilic regions, as in a phospholipid or a detergent molecule. anabolism- System of biosynthetic reactions in a cell by which large molecules are made from smaller ones. anaerobic- Describes a cell, organism, or metabolic process that functions in the absence of air or, more precisely, in the absence of molecular oxygen (O2). anchorage dependence- Dependence of cell growth on attachment to a substratum. anchoring junction- Type of cell junction that attaches cells to neighboring cells or to the extracellular matrix. angiogenesis- Growth of new blood vessels by sprouting from existing ones. Antagonist- A muscle that can move the joint opposite to the movement produced by the agonist. anterior- Situated toward the head end of the body. anteroposterior- Describes the axis running from the head to the tail of the animal body. anticodon- Sequence of three nucleotides in a transfer RNA molecule that is complementary to a three-nucleotide codon in a messenger RNA molecule. apoptosis- Form of cell death, also known as programmed cell death, in which a 'suicide' program is activated within the cell, leading to fragmentation of the DNA, shrinkage of the cytoplasm, membrane changes and cell death without lysis or damage to neighboring cells. It is a normal phenomenon, occurring frequently in a multicellular organism. aqueous- Pertaining to water, as for example, in an aqueous solution. ATP (adenosine 5-triphosphate)- Nucleoside triphosphate composed of adenine, ribose, and three phosphate groups that is the principal carrier of chemical energy in cells. The terminal phosphate groups are highly reactive in the sense that their hydrolysis, or transfer to another molecule, takes place with release of a large amount of free energy. ATP synthase- Enzyme complex in the inner membrane of a mitochon-drion and the thylakoid membrane of a chloroplast that catalyzes the formation of ATP from ADP and inorganic phosphate during oxidative phosphorylation and photosynthesis, respectively. Also present in the plasma membrane of bacteria. ATPase- Enzyme that catalyzes a process involving the hydrolysis of ATP. A large number of different proteins have ATPase activity. autocrine signaling- Type of cell signaling in which a cell secretes signal molecules that act on itself or on other adjacent cells of the same type. axon- Long nerve cell process that is capable of rapidly conducting nerve impulses over long distances so as to deliver signals to other cells. axonal transport- Directed transport of organelles and molecules along a nerve cell axon. It can be anterograde (outward from the cell body) or retrograde (back toward the cell body). basal lamina (basal laminae)- Thin mat of extracellular matrix that separates epithelial sheets, and many other types of cells such as muscle or fat cells, from connective tissue. biarticulate-A muscle that crosses two joints binding site- A region on the surface of one molecule (usually a protein or nucleic acid) that can interact with another molecule through noncovalent bonding. Ca2+/calmodulin-dependent protein kinase (CaM kinase)- Protein kinase whose activity is regulated by the binding of Ca2+-activated calmodulin (Ca2+/calmodulin), and which indirectly mediates the effects of Ca2+ by phosphorylation of other proteins. cadherin- A member of a family of proteins that mediates Ca2+-dependent cellcell adhesion in animal tissues. calcium pump (Ca2+ ATPase)- Transport protein in the membrane of the sarcoplasmic reticulum of muscle cells (and elsewhere) that pumps Ca2+ out of the cytoplasm into the sarcoplasmic reticulum using the energy of ATP hydrolysis. calmodulin- Ubiquitous calcium-binding protein whose binding to other proteins is governed by changes in intracellular Ca2+ concentration. Its binding modifies the activity of many target enzymes and membrane transport proteins. calorie- Unit of heat. One calorie (small "c" is the amount of heat needed to raise the temperature of 1 gram of water by 1°C. A kilocalorie (1000 calories) is the unit used to describe the energy content of foods. CAM- see cell adhesion molecule CaM kinase- see Ca2+/calmodulin-dependent protein kinase CaM-kinase II- Multifunctional Ca2+/calmodulin-dependent protein kinase found in all animal cells that undergoes autophosphorylation when activated. It is especially abundant in brain and is thought to have a role in learning and memory in vertebrates. cAMP- see cyclic AMP carbohydrate- General term for sugars and related compounds containing carbon, hydrogen, and oxygen, usually with the empirical formula (CH2O)n. carbonyl group- Pair of atoms consisting of a carbon atom linked to an oxygen atom by a double bond (C=O). carboxyl group- Carbon atom linked both to an oxygen atom by a double bond and to a hydroxyl group. Molecules containing a carboxyl group are weak acidscarboxylic acids ( ). carboxyl terminus (C terminus)- The end of a polypeptide chain that carries a free a-carbonyl group. cardiac muscle- Specialized form of striated muscle found in the heart, consisting of individual heart muscle cells linked together by cell junctions. carrier protein- Membrane transport protein that binds to a solute and transports it across the membrane by undergoing a series of conformational changes. cartilage- Form of connective tissue composed of cells (chondrocytes) embedded in a matrix rich in type II collagen and chondroitin sulfate. caspase- Any of a family of intracellular proteases that are involved in initiating the cellular events of apoptosis. catabolism- General term for the enzyme-catalyzed reactions in a cell by which complex molecules are degraded to simpler ones with release of energy. Intermediates in these reactions are sometimes called catabolites. Cdk- see cyclin-dependent kinase cDNA -DNA molecule made as a copy of messenger RNA and therefore lacking the introns that are present in genomic DNA. cDNA clones represent DNA cloned from cDNA and a collection of such clones, usually representing the genes expressed in a particular cell type or tissue, is a cDNA library. cell adhesion molecule (CAM)- Protein on the surface of an animal cell that mediates cellcell binding or cellmatrix binding. cell proliferation- An increase in the number of cells as a result of cell growth and cell division. cell wall- Mechanically strong extracellular matrix deposited by a cell outside its plasma membrane. It is prominent in most plants, bacteria, algae, and fungi. Not present in most animal cells. central nervous system (CNS)- Main information-processing organ of the nervous system. In vertebrates it consists of the brain and spinal cord. cholesterol- Lipid molecule with a characteristic four-ring steroid structure that is an important component of the plasma membranes of animal cells. chondrocyte (cartilage cell)- Connective-tissue cell that secretes the matrix of cartilage. circadian clock- Internal cyclical process that produces a particular change in a cell or organism with a period of around 24 hours, for example the sleep-wakefulness cycle in humans. Circumduction- circular movement (combining flexion, extension, adduction, and abduction) with no shaft rotation. citric acid cycle (tricarboxylic acid (TCA) cycle, Krebs cycle)- Central metabolic pathway found in aerobic organisms. Oxidizes acetyl groups derived from food molecules to CO2 and H2O. In eucaryotic cells it occurs in the mitochondria. Closed Chain- An exercise in which the end segment of the exercised limb is fixed, or the end is supporting the weight. Most compound exercises are closed chain movements. coenzyme- Small molecule tightly associated with an enzyme that participates in the reaction that the enzyme catalyzes, often by forming a covalent bond to the substrate. Examples include biotin, NAD+, and coenzyme A. coenzyme A- Small molecule used in the enzymatic transfer of acyl groups in the cell. (See also acetyl CoA.) cofactor- Inorganic ion or coenzyme that is required for an enzyme's activity. collagen fibril -Extracellular structure formed by self-assembly of secreted fibrillar collagen subunits. An abundant constituent of the extracellular matrix in many animal tissues. collagen- Fibrous protein rich in glycine and proline that is a major component of the extracellular matrix and connective tissues. Exists in many forms: type I, the most common, is found in skin, tendon, and bone; type II is found in cartilage; type IV is present in basal laminae. compound- An exercise that involves two or more joint movements. concentric contraction- The muscle tension exceeds the resistance and the muscle shortens. connective tissue- Any supporting tissue that lies between other tissues and consists of cells embedded in a relatively large amount of extracellular matrix. Includes bone, cartilage, and loose connective tissue. connective-tissue cell- Any of the various cell types found in connective tissue, e.g. fibroblasts, cartilage cells (chondrocytes), bone cells (osteoblasts and osteocytes), fat cells (adipocytes) and smooth muscle cells. coupled reaction- Linked pair of chemical reactions in which the free energy released by one of the reactions serves to drive the other. creatine phosphate- see phosphocreatine cyclic AMP (cAMP)- Nucleotide that is generated from ATP by adenylyl cyclase in response to stimulation of many types of cell-surface receptors. cAMP acts as an intracellular signaling molecule by activating cyclic-AMP-dependent kinase (protein kinase A, PKA). It is hydrolyzed to AMP by a phosphodiesterase. cyclic AMP dependent protein kinase (protein kinase A, PKA)- Enzyme that phosphorylates target proteins in response to a rise in intracellular cyclic AMP. cyclin-dependent kinase (Cdk)- Protein kinase that has to be complexed with a cyclin protein in order to act. Different Cdk-cyclin complexes trigger different steps in the cell-division cycle by phosphorylating specific target proteins. cytokine- Extracellular signal protein or peptide that acts as a local mediator in cellcell communication. cytokine receptor- Type of cell-surface receptor whose ligands are cytokines such as interferons, growth hormone and prolactin, and which acts through the Jak-STAT pathway. cytokinesis- Division of the cytoplasm of a plant or animal cell into two, as distinct from the division of its nucleus (which is mitosis) cytoskeleton- System of protein filaments in the cytoplasm of a eucaryotic cell that gives the cell shape and the capacity for directed movement. Its most abundant components are actin filaments, microtubules, and intermediate filaments. delayed onset muscle soreness- Soreness brought on by unaccustomed exercise or stretching, usually perceived 12 to 48 hours after the unaccustomed bout. deoxyribonucleic acid- see DNA differentiation- Process by which a cell undergoes a change to an overtly specialized cell type. disaccharide- Carbohydrate molecule consisting of two covalently joined monosaccharide units. dissociation constant (Kd)- Measure of the tendency of a complex to dissociate. For components A and B and the binding equilibrium A + B AB, the dissociation constant is given by [A]/[AB], and it is smaller the tighter the binding between A and B. (See also association constant.) DNA (deoxyribonucleic acid)- Polynucleotide formed from covalently linked deoxyribonucleotide units. It serves as the store of hereditary information within a cell and the carrier of this information from generation to generation. DNA ligase- Enzyme that joins the ends of two strands of DNA together with a covalent bond to make a continuous DNA strand. DNA transcription- see transcription DOMS- see Delayed Onset Muscle Soreness Duration (TUT, TUL)- The number of sets or number of exercises, specifically for each muscle group. Duration may also include number of repetitions. eccentric contraction- The peak tension developed is less than the resistance, and the muscle elongates. ectoderm- Embryonic tissue that is the precursor of the epidermis and nervous system. eIFs- see eukaryotic initiation factors elastin- Hydrophobic protein that forms extracellular extensible fibres (elastic fibres) that give tissues their stretchability and resilience. elongation factor- Protein required for the addition of amino acids to growing polypeptide chains on ribosomes. endocrine cell- Specialized animal cell that secretes a hormone into the blood. Usually part of a gland, such as the thyroid or pituitary gland. endomysium- the delicate connective tissue that surrounds the individual skeletal muscle fibers and interconnects adjacent muscle fibers. endoplasmic reticulum (ER)- Labyrinthine membrane-bounded compartment in the cytoplasm of eucaryotic cells, where lipids are synthesized and membrane-bound proteins and secretory proteins are made. enzyme Protein- that catalyzes a specific chemical reaction. enzyme linked receptor- Major type of cell-surface receptor in which the cytoplasmic domain either has enzymatic activity itself or is associated with an intracellular enzyme. In both cases enzymatic activity is stimulated by ligand binding to the receptor. epinephrine- see adrenaline epimysium- a dense layer of collagen fibers. equilibrium- State where there is no net change in a system. For example, equilibrium is reached in a chemical reaction when the forward and reverse rates are equal. ER resident protein- Protein that remains in the endoplasmic reticulum (ER) or its membranes and carries out its function there, as opposed to proteins that are present in the ER only in transit. eukaryotic initiation factors- Peptide initiation factors from eukaryotic organisms. Over twelve factors are involved in peptide chain initiation, translational in eukaryotic cells. Many of these factors play a role in controlling the rate of MRNA translation. Eversion- Moving sole of foot away from medial plane. extracellular matrix- Complex network of polysaccharides (such as glycosaminoglycans or cellulose) and proteins (such as collagen) secreted by cells. Serves as a structural element in tissues and also influences their development and physiology. extension- Straightening the joint resulting in an increase of angle. FAK- see focal adhesion kinase Fas protein (Fas)- Membrane-bound receptor that initiates apoptosis in the receptor-bearing cell after binding to its ligand (Fas ligand). fat- Energy storage lipid in cells. It is composed of triglyceridesfatty acids esterified with glycerol. fat cell- Connective tissue cell that produces and stores fat in animals. fatty acid- Compound such as palmitic acid that has a carboxylic acid attached to a long hydrocarbon chain. Used as a major source of energy during metabolism and as a starting point for the synthesis of phospholipids. feedback inhibition- Type of regulation of metabolism in which an enzyme acting early in a reaction pathway is inhibited by a late product of that pathway. fibroblast- Common cell type found in connective tissue. Secretes an extracellular matrix rich in collagen and other extracellular matrix macromolecules. Migrates and proliferates readily in wounded tissue and in tissue culture. fibronectin- Extracellular matrix protein that is involved in adhesion of cells to the matrix and the guidance of migrating cells during embryogenesis. Integrins on the cell surface are receptors for fibronectin. flexion- Bending the joint resulting in a decrease of angle. focal adhesion kinase (FAK)- Cytoplasmic tyrosine kinase present at cell-matrix junctions (focal adhesions) in association with the cytoplasmic tails of integrins. focal adhesion, focal contact (adhesion plaque)- A type of anchoring cell junction, forming a small region on the surface of a fibroblast or other cell that is anchored to the extracellular matrix. Attachment is mediated by transmembrane proteins such as integrins, which are linked, through other proteins, to actin filaments in the cytoplasm. free energy (G)- The energy that can be extracted from a system to drive reactions. Takes into account changes in both energy and entropy. free ribosome- Ribosome that is free in the cytosol, unattached to any membrane. It is the site of synthesis of all proteins encoded by the nuclear genome other than those destined to enter the endoplasmic reticulum. free-energy change (DG)- Change in the free energy during a reaction: the free energy of the product molecules minus the free energy of the starting molecules. A large negative value of DG indicates that the reaction has a strong tendency to occur. Frequency- The number of workouts per week (or unit time) or number times a muscle group is trained per week (or unit time). G- see free energy gap junction- Communicating cellcell junction that allows ions and small molecules to pass from the cytoplasm of one cell to the cytoplasm of the next. gene activator protein- A gene regulatory protein that when bound to its regulatory sequence in DNA activates transcription. gene control region- DNA sequences required to initiate transcription of a given gene and control the rate of initiation. gene conversion- Process by which DNA sequence information can be transferred from one DNA helix (which remains unchanged) to another DNA helix whose sequence is altered. It occurs occasionally during general recombination. gene regulatory protein- General name for any protein that binds to a specific DNA sequence to alter the expression of a gene. gene repressor protein- A gene regulatory protein that prevents the initiation of transcription. glucose- Six carbon sugar that plays a major role in the metabolism of living cells. Stored in polymeric form as glycogen in animal cells and as starch in plant cells. glycerol- Small organic molecule that is the parent compound of many small molecules in the cell, including phospholipids. glycogen- Polysaccharide composed exclusively of glucose units used to store energy in animal cells. Large granules of glycogen are especially abundant in liver and muscle cells. glycolysis- Ubiquitous metabolic pathway in the cytosol in which sugars are incompletely degraded with production of ATP. (Literally, "sugar splitting." growth factor- Extracellular polypeptide signal molecule that can stimulate a cell to grow or proliferate. Examples are epidermal growth factor (EGF) and platelet-derived growth factor (PDGF). Most growth factors also have other actions. GTP (guanosine 5-triphosphate)- Nucleoside triphosphate produced by phosphorylating GDP (guanosine diphosphate). Like ATP it releases a large amount of free energy on hydrolysis of its terminal phosphate group. It has a special role in microtubule assembly, protein synthesis, and cell signaling. GTPase Enzyme- activity that converts GTP to GDP. Also the common name used for monomeric GTP-binding proteins. GTPase activating protein (GAP)- Protein that binds to a GTP-binding protein and inactivates it by stimulating its GTPase activity so that it hydrolyzes its bound GTP to GDP. heat shock protein (stress-response protein)- Protein synthesized in increased amounts in response to an elevated temperature or other stressful treatment, and which usually helps the cell to survive the stress. Prominent examples are hsp60 and hsp70. hepatocyte- Liver cell. hormone- Signal molecule secreted by an endocrine cell into the bloodstream, which can then carry it to distant target cells. housekeeping gene- Gene serving a function required in all the cell types of an organism, regardless of their specialized role. hydrolysis (adjective hydrolytic)- Cleavage of a covalent bond with accompanying addition of water, H being added to one product of the cleavage and OH to the other. hydrophilic- Describes a polar molecule or part of a molecule that forms enough energetically favorable interactions with water molecules to dissolve readily in water. (Literally, "water loving." hydrophobic (lipophilic)- Describes a nonpolar molecule or part of a molecule that cannot form energetically favorable interactions with water molecules and therefore does not dissolve in water. (Literally, "water hating." Hyperextension- extending the joint beyond anatomical position. Hypoxia- Reduction of oxygen supply to tissues due to ischemia or acidosis. IGF-1– A well-characterized basic peptide believed to be secreted by the liver and to circulate in the blood. It has growth-regulating, insulin-like, and mitogenic activities. This growth factor has a major, but not absolute, dependence on GROWTH HORMONE. It is believed to be mainly active in adults in contrast to IGF-II, which is a major fetal growth factor. IGF-1E splice variants- Isoforms derived from the IGF-I gene by a process of alternative splicing, whereby exons are spliced in different combinations from the primary RNA transcript. isometric contraction- The muscle as a whole does not change length, and the tension produced never exceeds the resistance. in situ hybridization- Technique in which a single-stranded RNA or DNA probe is used to locate a gene or a messenger RNA molecule in a cell or tissue by hybridization. in vitro -Term used by biochemists to describe a process taking place in an isolated cell-free extract. Also used by cell biologists to refer to cells growing in culture (in vitro), as opposed to in an organism (in vivo). (Latin for "in glass." in vivo- In an intact cell or organism. (Latin for "in life." inflammatory response- Local response of a tissue to injury or infectioncharacterized by tissue redness, swelling, heat, and pain. Caused by invasion of white blood cells, which release various local mediators such as histamine. inhibitor of apoptosis family- see IAP family inhibitory neurotransmitter- Neurotransmitter that opens transmitter-gated Cl or K+ channels in the postsynaptic membrane of a nerve or muscle cell and thus tends to inhibit the generation of an action potential. initiation factor- Protein that promotes the proper association of ribosomes with messenger RNA and is required for the initiation of protein synthesis. initiator tRNA- Special tRNA that intiates translation. It always carries the amino acid methionine. insulin- Polypeptide hormone that is secreted by b cells in the pancreas and helps regulate glucose metabolism in animals. integrin- Member of a large family of transmembrane proteins involved in the adhesion of cells to the extracellular matrix and to each other. interleukin- Secreted peptide or protein that mainly mediates local interactions between white blood cells (leucocytes) during inflammation and immune responses. Intensity- The amount of weight used, percentage of the one repetition maximum. intermediate filament- Fibrous protein filament (about 10 nm in diameter) that forms ropelike networks in animal cells. One of the three most prominent types of cytoskeletal filaments. interstitial space- Relating to or situated in the small, narrow spaces between tissues or parts of an organ. intracellular signaling protein- Protein that relays a signal as part of an intracellular signaling pathway. It may either activate the next protein in the pathway or generate a small intracellular mediator. Inversion- Moving sole of foot toward medial plane. ion channel- Transmembrane protein complex that forms a water-filled channel across the lipid bilayer through which specific inorganic ions can diffuse down their electrochemical gradients. Ischemia-The reduction or blockage of blood flow to a tissue, cell or organ. isolated- An exercise that involves just one discernible joint movement. isotonic Contractions- Tension rises and the skeletal muscle's length changes. joule- Standard unit of energy in the meter-kilogram system. One joule is the energy delivered in one second by a one-watt power source. Approximately equal to 0.24 calories. K- see equilibrium constant ketone- Organic molecule containing a carbonyl group linked to two alkyl groups. kilocalorie (kcal)-Unit of heat energy equal to 1000 calories. Often used to express the energy content of food or molecules: bond strengths, for example, are measured in kcal/mole. An alternative unit in wide use is the kilojoule, equal to 0.24 kcal. kilojoule- Standard unit of energy equal to 1000 joules, or 0.24 kilocalories. kinesin-One type of motor protein that uses the energy of ATP hydrolysis to move along a microtubule. Krebs cycle- see citric acid cycle ligand- Any molecule that binds to a specific site on a protein or other molecule. (From Latin ligare, to bind.) ligase Enzyme- that joins together (ligates) two molecules in an energy-dependent process. DNA ligase, for example, joins two DNA molecules together end to end through phosphodiester bonds. lipid- Organic molecule that is insoluble in water but tends to dissolve in nonpolar organic solvents. A special class, the phospholipids, forms the structural basis of biological membranes. lipid bilayer- Thin bimolecular sheet of mainly phospholipid molecules that forms the core structure of all cell membranes. The two layers of lipid molecules are packed with their hydrophobic tails pointing inward and their hydrophilic heads outward, exposed to water. low-density lipoprotein (LDL)- Large complex composed of a single protein molecule and many esterified cholesterol molecules, together with other lipids. The form in which cholesterol is transported in the blood and taken up into cells. macrophage- Phagocytic cell derived from blood monocytes, typically resident in most tissues. It has both scavenger and antigen-presenting functions in immune responses. MAP-kinase (mitogen-activated protein kinase)- Protein kinase that performs a crucial step in relaying signals from the plasma membrane to the nucleus. Turned on by a wide range of proliferation- or differentiation-inducing signals. matrix space- (1) Central subcompartment of a mitochondrion, bounded by the inner mitochondrial membrane. (2) The corresponding compartment in a chloroplast, which is more commonly known as the stroma. mechano growth factor (IGF-1Eb,c) - see IGF-1 splice variants mechanotransduction - The process by which cells convert mechanical stimuli into a chemical response. It can occur in both cells specialized for sensing mechanical cues such as MECHANORECEPTORS, and in parenchymal cells whose primary function is not mechanosensory. membrane- The lipid bilayer plus associated proteins that encloses all cells and, in eucaryotic cells, many organelles as well. membrane transport- Movement of molecules across a membrane mediated by a membrane transport protein. membrane transport protein- Membrane protein that mediates the passage of ions or molecules across a membrane. Examples are ion channels and carrier proteins. messenger RNA (mRNA)- RNA molecule that specifies the amino acid sequence of a protein. Produced by RNA splicing (in eucaryotes) from a larger RNA molecule made by RNA polymerase as a complementary copy of DNA. It is translated into protein in a process catalyzed by ribosomes. metabolism- The sum total of the chemical processes that take place in living cells. MGF- see mechano growth factor microfilament- see actin filament microtubule- Long hollow cylindrical structure composed of the protein tubulin. It is one of the three major classes of filaments of the cytoskeleton. mitochondrion (mitochondria)- Membrane-bounded organelle, about the size of a bacterium, that carries out oxidative phosphorylation and produces most of the ATP in eucaryotic cells. mitogen- An extracellular substance, such as a growth factor, that stimulates cell proliferation. mitogen-activated protein kinase- see MAP-kinase monocyte- Type of white blood cell that leaves the bloodstream and matures into a macrophage in tissues. monomer Small molecular building block that can serve as a subunit, being linked to others of the same type to form a larger molecule (a polymer). monosaccharide- Simple sugar with the general formula (CH2O)n, where n = 3 to 8. motor protein- Protein that uses energy derived from nucleoside triphosphate hydrolysis to propel itself along a protein filament or another polymeric molecule. motor unit - All of the muscle cells controlled by a single motor neuron. mRNA- see messenger RNA myoblast- Mononucleated, undifferentiated muscle precursor cell. A skeletal muscle cell is formed by the fusion of multiple myoblasts. myofibril- Long, highly organized bundle of actin, myosin, and other proteins in the cytoplasm of muscle cells that contracts by a sliding filament mechanism. Na+-K+ pump (Na+-K+ ATPase)- Transmembrane carrier protein found in the plasma membrane of most animal cells that pumps Na+ out of and K+ into the cell, using energy derived from ATP hydrolysis. NAD+ (nicotine adenine dinucleotide)- Activated carrier that participates in an oxidation reaction by accepting a hydride ion (H) from a donor molecule. The NADH formed is an important carrier of electrons for oxidative phosphorylation. NADH dehydrogenase complex- First of the three electron-driven proton pumps in the mitochondrial respiratory chain. It accepts electrons from NADH. NADP+ (nicotine adenine dinucleotide phosphate)- Activated carrier closely related to NAD+ that is used extensively in biosynthetic, rather than catabolic, pathways. The reduced form is NADPH. N-CAM- see neural cell adhesion molecule negative staining- Staining technique for use in the electron electron microscope in which a reverse, or negative, image of the object is created. nerve cell- see neuron neural cell adhesion molecule (N-CAM)- Cell adhesion molecule of the immunoglobulin superfamily, expressed by many cell types including most nerve cells. It mediates Ca2+-independent cell-cell attachment in vertebrates. neurofilament- Type of intermediate filament found in nerve cells. neuromuscular junction- Specialized chemical synapse between an axon terminal of a motor neuron and a skeletal muscle cell. neuron (nerve cell)- Cell with long processes specialized to receive, conduct, and transmit signals in the nervous system. neuropeptide- Peptide secreted by neurons as a signaling molecule either at synapses or elsewhere. neurotransmitter- Small signal molecule secreted by the presynaptic nerve cell at a chemical synapse to relay the signal to the postsynaptic cell. Examples include acetylcholine, glutamate, GABA, glycine, and many neuropeptides. nicotine adenine dinucleotide phosphate- see NADP+ nicotine adenine dinucleotide- see NAD+ nitric oxide (NO)- Gaseous signal molecule in both animals and plants. In animals it regulates smooth muscle contraction, for example; in plants it is involved in responses to injury or infection. NO- see nitric oxide Notch Receptor- protein involved in many instances of choice of cell fate in animal development, for example in the specification of nerve cells from ectodermal epithelium. Its ligands are cell-surface proteins such as Delta and Serrate. nucleic acid RNA or DNA- a macromolecule consisting of a chain of nucleotides joined together by phosphodiester bonds. Occlusion-An obstruction or a closure of a body passage causing hypoxia or ischemia. Open Chain- An exercise in which the end segment of the exercised limb is not fixed, or the end is not supporting the weight. Most isolated exercises are open chain movements. oxidation (verb oxidize)- Loss of electrons from an atom, as occurs during the addition of oxygen to a molecule or when a hydrogen is removed. Opposite of reduction. oxidative phosphorylation- Process in bacteria and mitochondria in which ATP formation is driven by the transfer of electrons from food molecules to molecular oxygen. Involves the intermediate generation of a proton gradient (pH gradient) across a membrane and chemiosmotic coupling. paracrine signaling- Short-range cell-cell communication via secreted signal molecules that act on adjacent cells. phosphatase- Enzyme that removes phosphate groups from a molecule. phosphatidylinositol 3-kinase (PI 3-kinase)- A kinase involved in intracellular signaling pathways activated by a variety of cell-surface receptors. It phosphorylates inositol phospholipids at the 3 position of the inositol ring. phosphocreatine- an organic compound of creatine and phosphoric acid; found in the muscles of vertebrates where its hydrolysis releases energy for muscular contraction. phosphorylation- Reaction in which a phosphate group becomes covalently coupled to another molecule. polypeptide- Linear polymer composed of multiple amino acids. Proteins are large polypeptides, and the two terms can be used interchangeably. polysaccharide- Linear or branched polymer of monosaccharides. They include glycogen, starch, hyaluronic acid, and cellulose. posterior- Situated toward the tail end of the body. postprandial- Happening or done after a meal. posttranscriptional control- Any control on gene expression that is exerted at a stage after transcription has begun. posttranslational- Describes any process involving a protein that occurs after protein synthesis is completed. posttranslational modification- The enzyme-catalyzed change to a protein made after it is synthesized. Examples are acetylation, cleavage, glycosylation, methylation, phosphorylation, and prenylation. programmed cell death- see apoptosis proliferation- see cell proliferation promoter- Nucleotide sequence in DNA to which RNA polymerase binds to begin transcription. pronation- Internal rotation resulting in appendage facing downward. protein- The major macromolecular constituent of cells. A linear polymer of amino acids linked together by peptide bonds in a specific sequence. protein kinase- Enzyme that transfers the terminal phosphate group of ATP to a specific amino acid of a target protein. protein kinase C (PKC)- Ca2+-dependent protein kinase that, when activated by diacylglycerol and an increase in the concentration of Ca2+, phosphorylates target proteins on specific serine and threonine residues. protein phosphorylation- The covalent addition of a phosphate group to a side chain of a protein catalyzed by a protein kinase. proteolysis- Degradation of a protein by hydrolysis at one or more of its peptide bonds. protrusion- Moving anteriorly (eg: chin out). Ras protein- The most famous member of a large family of GTP-binding proteins (called monomeric GTPases) that help relay signals from cell-surface receptors to the nucleus. Named for the ras gene, first identified in viruses that cause rat sarcomas. rate coding - the firing frequency of the Motor Neurons receptor- Protein that binds a specific extracellular signal molecule (ligand) and initiates a response in the cell. Cell-surface receptors, such as the acetylcholine receptor and the insulin receptor, are located in the plasma membrane, with their ligand-binding site exposed to the external medium. Intracellular receptors, such as steroid hormone receptors, bind ligands that diffuse into the cell across the plasma membrane. respiration- General term for a process in a cell involving the oxidative breakdown of sugars or other organic molecules, and requiring the uptake of O2 while producing CO2 and H2O as waste products. retrusion- Moving posteriorly (eg: chin in). ribonucleic acid- see RNA ribosomal RNA (rRNA)- Any one of a number of specific RNA molecules that form part of the structure of a ribosome and participate in the synthesis of proteins. Often distinguished by their sedimentation coefficient, such as 28S rRNA or 5S rRNA. ribosome- Particle composed of ribosomal RNAs and ribosomal proteins that associates with messenger RNA and catalyzes the synthesis of protein. RNA (ribonucleic acid)- Polymer formed from covalently linked ribonucleotide monomers. (See also messenger RNA, ribosomal RNA, transfer RNA.) rotation- Rotary movement around the longitudinal axis of the bone. sarcolemma - The cell membrane of a muscle cell. sarcomere- Repeating unit of a myofibril in a muscle cell, composed of an array of overlapping thick (myosin) and thin (actin) filaments between two adjacent Z discs. sarcoplasmic reticulum- Network of internal membranes in the cytoplasm of a muscle cell that contains high concentrations of sequestered Ca2+ which is released into the cytosol during muscle excitation. satellite cell- Quiescent cells located outside the muscle fibre sarcolemma but beneath the basement lamina, which become activated by stimulation, like muscle fibre injury or increased muscle tension, start replicating and are responsible for the repair of injured muscle fibres and the growth of muscle fibres. (also see Stem cell) scaffold protein- Protein that organizes groups of interacting intracellular signaling proteins into signaling complexes. second messenger- Small molecule that is formed in or released into the cytosol in response to an extracellular signal and helps to relay the signal to the interior of the cell. Examples include cAMP, IP3, and Ca2+. signal molecule- Extracellular or intracellular molecule that cues the response of a cell to the behavior of other cells or objects in the environment. signal transduction- Relaying of a signal by conversion from one physical or chemical form to another. In cell biology, the process by which a cell converts an extracellular signal into a response. smooth muscle cell- Type of long, spindle-shaped mononucleate muscle cell making up the muscular tissue found in the walls of arteries and of the intestine and other viscera, and in some other locations of the vertebrate body. Called "smooth" because it lacks the striated myofibrils of skeletal and cardiac muscle cells. supination- External rotation resulting in appendage facing upward. stabilizer- A muscle that contracts with no significant movement. starch- Polysaccharide composed exclusively of glucose units, used as an energy storage material in plant cells. stem cell- Relatively undifferentiated cell that can continue dividing indefinitely, throwing off daughter cells that can undergo terminal differentiation into particular cell types. steroid- Hydrophobic lipid molecule with a characteristic four-ringed structure. Many important hormones such as estrogen and testosterone are steroids. stimulatory G protein (Gs)- G protein that, when activated, activates the enzyme adenylyl cyclase and thus stimulates the production of cyclic AMP. striated muscle- Muscle composed of transversely striped (striated) myofibrils. Skeletal and heart muscle of vertebrates are the best-known examples. substrate- Molecule on which an enzyme acts. sucrose- Disaccharide composed of one glucose unit and one fructose unit. The major form in which glucose is transported between plant cells. sugar- Small carbohydrates with a monomer unit of general formula (CH2O)n. Examples are the monosaccharides glucose, fructose and mannose, and the disacharide sucrose (composed of a molecule of glucose and one of fructose linked together). synapse- Communicating cellcell junction that allows signals to pass from a nerve cell to another cell. In a chemical synapse the signal is carried by a diffusible neurotransmitter; in an electrical synapse a direct connection is made between the cytoplasms of the two cells via gap junctions. synaptic signaling- Type of cellcell communication that occurs across chemical synapses in the nervous system. synaptic vesicle- Small neurotransmitter-filled secretory vesicle formed at the axon terminals of nerve cells and whose contents are released into the synaptic cleft by exocytosis when an action potential reaches the axon terminal. Synergist- A muscle that assists another muscle to accomplish a movement. T-Tubule- See Transverse Tubule TCA cycle- see citric acid cycle TGFb-Super Family of Transforming Growth Factors transcript- RNA product of DNA transcription. transcription (DNA transcription)- Copying of one strand of DNA into a complementary RNA sequence by the enzyme RNA polymerase. transcription factor- Term loosely applied to any protein required to initiate or regulate transcription in eucaryotes. Includes both gene regulatory proteins as well as the general transcription factors. transcriptional control- Control of of gene expression by controlling when and how often the gene is transcribed. transfer RNA (tRNA)- Set of small RNA molecules used in protein synthesis as an interface (adaptor) between messenger RNA and amino acids. Each type of tRNA molecule is covalently linked to a particular amino acid. transforming growth factor-b superfamily (TGF-b superfamily)- Large family of structurally related, secreted proteins that act as hormones and local mediators to control a wide range of functions in animals, including during development. It includes TGF-bs, activins, and bone morphogenetic proteins (BMPs). translation (RNA translation)- Process by which the sequence of nucleotides in a messenger RNA molecule directs the incorporation of amino acids into protein. It occurs on a ribosome. Transverse Tubule- Narrow tubes that are continuous with the sarcolemma and extend into the sarcoplasm at right angles to the cell surface. Triarticulate- A muscle that can move three joints. TUT (TUL)-Time under tension, load. (see also Duration) ubiquitin- Small, highly conserved protein present in all eucaryotic cells that becomes covalently attached to lysines of other proteins. Attachment of a short chain of ubiquitins to such a lysine tags a protein for intracellular proteolytic destruction by a proteasome. ubiquitin ligase- Any one of a large number of enzymes that attach ubiquitin to a protein, thus marking it for destruction in a proteasome. The process catalyzed by a ubiquitin ligase is called ubiquitylation. unfolded protein response- Cellular response triggered by an accumulation of misfolded proteins in the endoplasmic reticulum. It involves increased transcription of ER chaperones and degradative enzymes. Uniarticulate- A muscle that crosses one joint. voltage-gated cation channel- Type of ion channel found in the membranes of excitable cells (such as nerve cells and muscle) which opens in response to a shift in membrane potential past a threshold value. Western blotting- Technique by which proteins are separated by electrophoresis and immobilized on a paper sheet and then analyzed, usually by means of a labeled antibody. wild-type- Normal, nonmutant form of an organism; the form found in nature (in the wild). Z disc (Z line)- Platelike region of a muscle sarcomere to which the plus ends of actin filaments are attached. Seen as a dark transverse line in micrographs.