UCSB ChE 170 Essay

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Action Potential
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Rapid, transient, self-propagating electrical signal in the plasma membrane of a cell such as a neuron or muscle. A nerve impulse.
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Activator
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A protein that binds to a specific regulatory region of DNA to permit transcription of an adjacent gene
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Active Transport
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Movement of a molecule across a membrane driven by ATP hydrolysis or another form of metabolic energy
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Adaptation
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Adjustment of sensitivity of a cell or organism following repeated stimulation. Can allow a response even when there is a high background level of stimulation
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Adenosine Triphosphate (ATP)
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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, is accompanied by the releas of a large amount of free energy.
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Adenylyl Cyclase
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Enzyme that catalyzes the formation of cyclic AMP from ATP. An important component of some intracellular signaling pathways
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Affinity
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How tightly a given molecule bonds
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Allosteric
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Describes a protein that can exist in two or more conformations depending on the binding of a molecule (a ligand) at a site other than the catalytic site.  Proteins composed of multiple subunits often display a cooperative response to lingand binding, because the binding of a ligand to one subunit facilitates the binding of ligands to the other subunits.
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Alpha Helix
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Common structural motif of proteins in which a linear sequence of amino acids folds into a right-handed helix stabilized by internal hydrogen bonding between back-bone atoms
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Amino Acid
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Organic molecule containing both an amino group and a carboxyl group
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Amphipathic
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Having both hydrophobic and hydrophilic regions, as in a phospholipid or a detergent molecule
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Anabolism
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Reaction pathways by which large molecules are made from smaller ones. Biosynthesis.
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Antibody
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Protein produced by B lymphocytes in response to a foreign molecule or invading organism. Binds to the foreign molecule or cell extremely tightly, thereby inactivating it or marking it for destruction.
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Antigen
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Molecule that provokes the production of specific neutralizing antibodies in an immune response
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Antiport
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Type of coupled transporter that transports two different ions or small molecules across a membrane in opposite directions, either simultaneously or in sequence.
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Archea
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One of the two divisions of procaryotes, often found in hostile environments such as hot springs or concentrated brine
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Bacteria
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Commonly used name for any procaryotic organism, but more precisely refers to the eu********, the “true ********,” one of the three major domains of life. Most are single-celled organisms. Some species of ******** cause disease
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Base Pair
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Two nucleotides in an RNA or a DNA molecule that are specifically pared by hydrogen bonds – for example, G with C, and A with T or U
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Beta Sheet
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Folding pattern found in many proteins in which neighboring regions of the polypeptide chain associate side by side with each other through hydrogen bonds to give a rigid, flattened structure
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Binding Site
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Region on the surface of a protein, typically a cavity or groove, that is complementary in shape to, and forms multiple noncovalent bonds with, a second molecule (the ligand)
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Ca2+/Calmodulin-Dependeint Protein Kinase (CaM-kinase)
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Enzyme that phosphorylates target proteins in response to an increase in Ca2+ ion concentration, through its interaction with the Ca2+ binding protein calmodulin
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Calmodulin
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Small Ca2+ binding protein that modifies the activity of many target enzymes and membrane transport proteins in response to changes in Ca2+ concentration
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Cancer
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Disease caused by abnormal and uncontrolled cell division resulting in localized growths, or tumors, which may spread throughout the body
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Catabolism
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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 *******ites
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Cell Cortex
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Specialized layer of cytoplasm on the inner face of the plasma membrane. In animal cells it is an actin-rich layer responsible for cell-surface movements.
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Cell Junction
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Specialized region of connection between two cells or between a cell and the extracellular matrix
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Cell Signaling
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The molecular mechanisms by which cells detect and respond to external stimuli and send messages to other cells
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Cell Wall
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Mechanically strong fibrous layer deposited by a cell outside its plasma membrane. Prominent in most plants, bacteria, algae, and fungi, but not present in most animal cells
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Cellulose
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Structural polysaccharide consisting of long chains of covalently linked glucose units. It provides tensile strength in plant cell walls.
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Centromere
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Constricted region of a mitotic chromosome that holds sister chromatids together; also the site on the DNA where the kinetochore forms and then captures microtubules from the mitotic spindle
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Centrosome (Cell Center)
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Centrally located organelle of animal cells that is the primary microtubule-organizing center and separates to form the two spindle poles during mitosis. In most animal cells it containes a pare of centrioles.
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Channels
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An aqueous pore in a lipid membrane, with walls made of protein, through which selected ions or molecules can pass
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Chloroplast
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Specialized organelle in algae and plants that contains chlorophyll and in which photosynthesis takes place
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Cholesterol
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Lipid molecule with a characteristic four-ringed steroid structure that is an important component of the plasma membranes in animal cells
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Chromatin
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Complex of DNA, histones, and nonhistone proteins found in the nucleus of a eucaryotic cell
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Chromosome
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Long threadlike structure composed of DNA and associated proteins that carries the genetic information of an organism. Especially visible when plant and animal cells undergo mitosis or meiosis.
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Clathrin
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Protein that makes up the coat of one type of transport vesicle. Vesicles coated in this bud from the Golgi apparatus on the outward secretory pathway and bud from the plasma membrane on the inward endocytic pathway
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Coated Vesicle
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Small membrane-enclosed organelle with a cage of proteins (the coat) on its cytosolic surface. It is formed by the pinching off of a protein coated region of membrane
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Codon
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Sequence of three nucleotides in a DNA or messenger RNA molecule that represents the instruction for incorporation of a specific amino acid into a growing polypeptide chain.
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Collagen
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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 and so on.
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Combinatorial Control
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Describes the way in which groups of proteins work together in combination to control the expression of a single gene
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Condensation Reaction
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Type of chemical reaction in which two organic molecules become linked to each other by a covalent bond with concomitant removal of a molecule of water
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Connective Tissue
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Tissues such as bone, tendons, and the dermis of the skin, in which extracellular matrix is plentiful and carries the mechanical load
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Coupled Transporter
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Membrane transport protein that carries out transport in which the transfer of one molecule depends on the simultaneous or sequential transfer of a second molecule
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Cyclic AMP
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Nucleotide generated from ATP in response to hormonal stimulation of cell-surface receptors. Acts as a signaling molecule by activating protein kinase A; it is hydrolyzed by a phosphodiesterase
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Cyclic-AMP-dependent Protein Kinase
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Enzyme that phosphorylates target proteins in response to a rise in intracellular cyclic AMP concentration
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Cytokine
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Small protein made and secreted by cells that acts on neighboring cells to alter their behavior. Act via cell-surface receptors.
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Cytoplasm
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Contents of a cell that are contained within its plasma membrane but, in the case of eucaryotic cells, outside the nucleus
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Cytoskeliton
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System of protein filaments in the cytoplasm of a eucaryotic cell that gives the cell shape and the capacity for directed movement. Its most abundent components are actin filiments, microtubules, and intermediate filiments.
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Cytosol
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Contents of the main compartment of the cytoplasm, excluding membrane-enclosed organelles such as the ER and mitochondria. The cell fraction remaining after membranes, cytoskelital components, and other organelles have been removed.
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Denature
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To cause adramatic change in the conformation of a protein or nucleic acid by heating it or by exposing it to chemicals. Usually results in the loss of biological function.
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Diacylglycerol (DAG)
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Lipid produced by the cleavage of membrane inositol phospholipids in response to extracellular signals. Composed of two fatty acid chains linked to glycerol, it serves as a membrane-located signaling molecule to help activate protein kinase C.
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Differentiation
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Process by which a cell undergoes a progressive change to a more specialized and usually easily recognized cell type
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Disulfide Bond
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Covalent linkage formed between two sulfhydryl groups on cysteins. Common way to join two proteins or to link together different parts of the same protein in the extracellular space.
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DNA
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Double-stranded polynucleotide formed from two separate chains of covalently linked deoxyribonucleotide units. It serves as the cell’s store of genetic information that is transmitted from generation to generation.
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DNA Methylation
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The enzymatic addition of methyl groups to cytosine bases in DNA. Methylation generally turns off genes by attracting proteins that block gene expression
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Dynein
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Member of a family of large motor proteins that undergo ATP-dependent movement along microtubules. Responsible for the bending of cilia.
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Electrostatic Interaction
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Interaction involving formal electric charges
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Endocytosis
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Uptake of material into a cell by an invagination of the plasma membrane and its internalization in a membrane-bounded vesicle
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Endoplasmic Reticulum (ER)
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Labrinthine, membrane-enclosed compartment in the cytoplasm of eukaryotic cells, where lipids and secreted and membrane-bound proteins are made
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Endosome
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Membrane-enclosed compartment of a eukaryotic cell through which endocytosed material passes on its way to the lysosomes
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Endrocrine Signaling
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Signaling involving hormone movement over long distances
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Enzyme-coupled Receptor
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Transmembrane receptor proteins that activate an intracellular enzyme in response to ligand binding to the extracellular part of the receptor
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Epigenetic Inheritance
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Inheritance that is superimposed on the information that is inherited in the DNA sequence itself. Often, information in the form of a particular type of chromatin structure (eg a certain pattern of histone modification or DNA methylation)
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Epithelial Tissue
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Close packed cells covering the surface of the body
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Eucaryote
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Living organism composed of one or more cells with a distinct nucleus and cytoplasm. Includes all forms of life except archaea, bacteria and viruses.
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Exocytosis
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Process by which most molecules are secreted from a eukaryotic cell. These molecules are packaged in membrane-enclosed vesicles that fuse with the plasma membrane, releasing their contents to the outside
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Extracellular Matrix
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Complex network of polysaccharides (such as glycosaminoglycans or cellulose) and proteins (such as collagen) secreted by cells. A structural component of tissues that also influences their development and physiology.
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Extracellular Signal Molecule
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Any molecule present outside the cell that can elicit a response inside the cell when the molecule binds to a receptor protein. Some signal molecules, such as steroid hormones, can enter cells and act on internal receptors embedded in the plasma membrane and exposed on the cell surface
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Fatty Acid
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Compound such as palmitic acid that has a corboxylic 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.
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Fibroblast
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Common cell type found in connective tissue that secretes an extracellular matrix rich in collagen and other extracellular matrix macromolecules. Migrates and proliferates readily in wounded tissue and in tissue culture.
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Fibronectin
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Extracellular matrix protein that binds to integrins on cell surfaces, helping cells to adhere to the matrix
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Fibrous Protein
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A protein with an elongated shape. Typically one such as collagen or intermediate filament protein that is able to associate into long filamentous structures.
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Free Energy Transduction
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The use of free energy of one source in order to drive another reaction
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G protein
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One of a large family of GTP-binding proteins composed of three different subunits that are important intermediaries in intracellular signaling pathways. Usually activated by the binding of a hormone or other ligand to a transmembrane receptor
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Gene
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Region of DNA that controls a discrete hereditary characteristic of an organism, usualy responsible for specifying a single protein or RNA molecule
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Gene Expression
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The process by which a gene makes its effect on a cell or organism by directing the synthesis of a protein or an RNA molecule with a characteristic activity
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Genome
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The total genetic information carried by a cell or an organism (or the DNA molecules that carry this information)
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Gibbs Free Energy
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Energy that can be extracted from a system to do useful work, such as driving a chemical reaction
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Glucose
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Six-carbon sugar that plays a major role in the metabolism of living cells. Stored in polymeric form as glycogen in anial cells and as starch in plant cells.
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Glycolipid
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Membrane lipid molecule with a short carbohydrate chain atached to a hydrophobic tail
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Glycoprotein
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Any protein with one or more covalently linked oligosaccharide chains. Includes most secreted proteins and most proteins exposed on the outer surface of the plasma membrane.
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Glycosylation
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The addition of a sugar to a protein
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Golgi Apparatus
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Membrane-enclosed organelle in eukaryotic cells where the proteins and lipids made in the ER are modified and sorted for transport to other sites
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G-protein-coupled Receptor (CPCR)
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Cell-surface receptor that associates with an intracellular trimeric GTP-binding protein (G protein) after receptor activation by an extracellular ligand. These receptors are sevenpass transmembrane proteins
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GTP-binding Protein
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An allosteric protein whose conformation and activity are determined by its association with either GTP or GDP. Includes many proteins involved in cell signaling, such as Ras and G proteins
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Guanosine Triphosphate (GTP)
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Major nucleoside triphosphate used in the synthesis of RNA and in some energy-transfer reactions. Also has a special role in microtubule assembly, protein synthesis, and cell signaling.
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Histone
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One of a group of abundant basic proteins, rich in arginine and lysine, that are associated with DNA in chromosomes to form nucleosomes
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Homologous Recombination
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Genetic exchange between a pair of identical or very similar DNA sequences, typically located on a pair of homologous chromosomes. A similar process is used to repair double-strand breaks in DNA.
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Hormone
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A chemical substance produced by one set of cells in a multicellular organism and transported via body fluids to target tissues on which it exerts a specific effect
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Hydrolysis Reaction
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Cleavage of a covalent bond with accompanying addition of water, -H being added to one product of the cleavage and -OH of the other
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Hydrophobic Interaction
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Interaction forming partial electric charges
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Immunoglobulin
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Alternative name for an antibody (abbreviated Ig)
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Inositol 1,4,5-trisphosphate (IP3)
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Small intracellular signaling molecule produced during activation of the inositol phospholipid signaling pathway; causes Ca2+ release from the ER
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Inositol Phospholipid
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Minor lipid components of plasma membranes that contain phosphorylated inositol derivatives; important both for distinguishing different intracellular membranes and for signal transduction in eukaryotic cells
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Integrins
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Family of transmemebrane proteins present on cell surfaces that enable cells to adhere to each other and to the extracellular matrix, being also involved in cell signaling
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Intracellular Signaling Molecule
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Molecule (usu protein) that is part of the mechanism for transducing and transmitting signals inside a cell
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Intracellular Signaling Pathway
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The set of proteins and small-molecule second-messengers that interact with each other to relay a signal from the cell membrane to its final destination in the cytoplasm or nucleus
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Intron
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Noncoding region of a eucaryotic gene that is transcribed into an RNA molecule but is then excised by RNA splicing to produce mRNA
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Ion Channel
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Transmembrane protein or protein complex that forms a water-filled channel across the lipid bilayer through which specific inorganic ions can diffuse down their electrochemical gradients
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Ion-channel-coupled Receptor
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Transmembrane receptor protein or complex that forms a gated ion chanel that opens in response to the binding of a ligand to the external face of the channel
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Keratin
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Fibrous structural protein making up the outer layer of skin, hair, nails, etc.
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Kinesin
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A large family of motor proteins that use the energy of ATP hydrolysis to move along a microtubule
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Lagging Strand
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One of the two newly made strands of DNA found at a replication fork. This strand is made of discontinuous lengths that are later joined covalently.
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Leading Strand
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One of the two newly made strands of DNA found at a replication fork. This strand is made by continuous synthesis in the 5′ to 3′ direction
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Ligand
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General term for a molecule that binds to a specific site on a protein
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Lipid
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Organic molecule that is insoluble in water but dissolves readily in nonpolar organic solvents. One class, the phospho******, forms the structural basis of biological membranes.
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Liposome
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Artificially made vesicles made of a lipid bilayer
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Local Mediator
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Secreted signal molecule that acts at a short range on adjacent cells
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Lysosome
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Intracellular membrane-enclosed organelle containing digestive enzymes, typically those most active at the acid pH found in these organelles
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MAP Kinase
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Mitogen-activated protein kinase. Protein kinase that performs a crucial step in relaying signals from cell-surface receptors to the nucleus. It is the final kinase in the three-kinase sequence called the MAP kinase cascade
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Membrane Potential
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Voltage difference across a membrane due to a slight excess of positive ions on one side and of negative ions on the other
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Membrane-enclosed Organelle
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Any organelle in the eucaryoti cell that is surrounded by a lipid bilayer membrane, for example, the ER, Golgi, and lysosome
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Messenger RNA (mRNA)
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RNA molecule that specifies the amino acid sequence of a protein. Produced by RNA splicing (in eucaryotes) from larger RNA molecule made by RNA polymerase as a complementary copy of DNA. It is translated into protein in a process catalyzed by ribosomes.
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MicroRNA (miRNA)
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Small noncoding RNAs that control gene expression by base-pairing with specific mRNAs to regulate their stability and their translation
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Mitochondria
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Membrane-enclosed organelle, about the size of a bacterium, that carries out oxidative phosphorylation and produces most of the ATP in eucaryotic cells
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Molecular Switch
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Protein or protein complex that operates in an intracellular signaling pathway and can reversibly switch between an active and inactive state
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Monomeric GTPase
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Small, single-subunit GTP- binding protein. Proteins of this family, such as Ras and Rho, are part of many different signaling pathways
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Motor Protein
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Protein such as myosin or kinesin that uses energy derived from ATP hydrolysis to propel itself along a protein filament or polymeric molecule
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Myosin
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Type of motor protein that uses ATP to drive movements along actin filaments. A large protein that forms the thick filaments of skeletal muscle. Smaller versions are widely distributed and are responsible for many actin-based movements.
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NAD+
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Activated carrier molecule that participates in an oxidation reaction by accepting a hydride ion (H-) from a donor molecule, thereby producing ***H. Widely used in the energy-producing breakdown of sugar molecules.
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NADPH
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A carrier molecule closely related to NADH used as an electron donor in biosynthetic pathways
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Neurotransmitter
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Small signaling molecule secreted by a nerve cell at a chemical synapse to signal the postsynaptic cell
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Nitric Oxide (NO)
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Small highly diffusible molecule widely used as an intracellular signal
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NMR Spectroscopy
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Technique used for determining the three-dimensional structure of a protein; it I performed in solution without requiring a protein crystal.
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Nuclear Envelope
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Double membrane surrounding the nucleus. Consists of outer and inner membranes perforated by nuclear pores
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Nuclear Lamina
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Fibrous layer on the inner surface of the inner nuclear membrane formed as a network of intermediate filaments made from nuclear lamins.
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Nuclear Pore
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Channel through the nuclear envelope that allows selected large molecules to move between the nucleus and cytoplasm
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Nuclear Receptor
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Receptor proteins present inside a eukaryotic cell that can bind to signal molecules that enter the cell, such as steroid hormones; the complex of nuclear receptor and signal molecule subsequently acts as a transcription regulator
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Nucleosomes
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Beadlike structural unit of a eucaryotic chromosome composed of a short length of DNA wrapped around a core of histone proteins; the fundamental subunit of chromatin
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Nucleotide
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Nucleoside with a series of one or more phosphate groups joined by an ester linkage to the sugar moiety. DNA and RNA are polymers of this.
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Organelle
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A discrete structure or subcompartment of a eucaryotic cell (especially one that is visible in the light microscope) that is specialized to carry out a particular function. Examples include mitochondria and the Golgi Apparatus.
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Osmotic Pressure
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Pressure that must be exerted on the low-solute concentration side of a semipermeable membrane to prevent the flow of water across the membrane as a result of osmosis
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Osteoblast
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Cells that make bone tissues
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Paracrine Signaling
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Signals passing via tissues
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Passive Transport
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The movement of a small molecule or ion across a membrane due to a difference in concentration or electrical charge
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Peptide Bond
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Chemical bond between the carbonyl group of one amino acid and the amino group of a second amino acid – a special form of amide linkage
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Peroxisome
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Small membrane-enclosed organelle that uses molecular oxygen to oxidize organic molecules. Contains some enzymes that produce hydrogen peroxide and others that degrade it
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Phagocytic Cell
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A cell such as a macrophage or neutrophil that is specialized to take up particles and microorganisms by phagocytosis
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Phagocytosis
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The process by which particulate material is engulfed by a cell.
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Phosphatase
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Enzyme that removes a phosphate group from its substrate
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Phosphoinositide 3-kinase (PI 3-kinase)
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Enzyme that phosphorylates inositol phospholipids in the ER in response to signals received by the cell. The phosphorylated lipids become docking sites for intracellular signaling proteins
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Phospholipase C
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Enzyme associated with the PM that performs a crucial step in the inositol phospholipid signaling pathways
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Phospholipid
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Type of lipid molecule used to make biological membranes. Generally composed of two fatty acids linked through glycerol phosphate to one of a variety of polar groups
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Phosphorylation
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The covalent addition of a phosphate group to a side chain of a protein catalyzed by a protein kinase. Usually alters the activity or properties of the protein in some way.
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Pinocytosis
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Type of endocytosis in which soluble materials are taken up from the environment and incorporated into vesicles for digestion (cell drinking)
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Plasma Membrane
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The membrane that surrounds a living cell
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Polymerase
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General term for an enzyme that catalyzes addition of subunits to a polymer
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Polysaccharide
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Linear or branched polymer composed of sugars. Examples are glycogen, hyaluronic acid, and cellulose.
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Positive Feedback Loop
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Situation in which the end product of a reaction stimulates its own production
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Post-Transcriptional Control
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Regulation of gene expression that occurs after transcription of the gene has begun; examples are regulation of RNA splicing and other RNA processing events, and regulation of translation by microRNA
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Procaryote
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Major category of living cells distinguished by the absence of a nucleus. Comprise the archaea and the eubacteria (commonly called bacteria), two of the three domains of life.
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Promoter
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Nucleotide sequence in DNA to which RNA polymerase binds to begin transcription
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Proofreading
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The process by which DNA polymerase corrects its own errors as it moves along DNA
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Protease
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Enzyme such as trypsin that degrades proteins by hydrolyzing some of their peptide bonds
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Proteasome
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Large protein complex in the cytosol that is responsible for degrading cytosolic proteins that have been marked for destruction by ubiquitylation or by some other means
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Protein Kinase
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One of a very large number of enzymes that transfers the terminal phosphate group of ATP to a specific amino acid side chain on a target protein
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Protein Kinase
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Transferrs the terminal phosphate group of ATP to a specific amino acid side chain or target protein
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Protein Kinase C (PKC)
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Enzyme that phosphorylates target proteins in response to a rise in diacylgycerol and Ca2+ ions
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Protein Phosphatase
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Enzyme that removes, by hydrolysis, a phosphate group from a protein, often with high specificity for the phosphorylated site
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Proteoglycan
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Molecule consisting of one or more glycosaminoglycan chains attached to a core protein
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Purines
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One of the two categories of nitrogen-containing ring compounds found in DNA and RNA. Examples are adenine and guanine.
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Pyrimidines
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One of the two categories of nitrogen-containing ring compounds found in DNA and RNA. An example is cytosine.
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Rab Protein
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A family of small GTP-binding proteins present on the surfaces of transport vesicles and organelles that serve as molecular markers identifying each membrane type. Rab proteins help to ensure that transport vesicles fuse only with the correct membrane
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Ras
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One of a large family of small GTP-binding proteins that helps relay signals from cell-surface receptors to the nucleus
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Reading Frame
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The set of successive triplets in which a string of nucleotides is translated into protein. An mRNA molecule is read in one of three possible of these, depending on the starting point.
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Receptor Protein
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Protein that detects a stimulus, usually a change in concentration of a specific molecule, and then 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 a steroid hormone receptors, bind ligands that diffuse into the cell across the plasma membrane.
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Receptor Serine/Threonine Kinase
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Enzyme coupled receptor with an extracellular signal-binding domain and an intracellular kinase domain that phosphorylates signaling proteins on serine or threonine
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Receptor Tyrosine Kinase (RTK)
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Enzyme coupled receptor in which the intracellular domain has a tyrosine kinase activity, which is activated by ligand binding to the receptor’s extra-cellular domain
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Receptor, Receptor Protein
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Detects a stimulus, usu a change in concentration, and then initiates a response in the cell
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Receptor-Mediated Endocytosis
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Mechanism of selective uptake of material by animal cells in which a macromolecule binds to a receptor in the plasma membrane and enters the cell in a clathrin-coated vesicle
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Regulatory DNA Sequence
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DNA sequence to which a transcription regulator binds to determine when, where, and in what quantities a gene is to be transcribed into RNA
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Replication Origin
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Site on a chromosome at which DNA replication begins
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Reporter Gene
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Introduced gene encoding a protein whose activity is easy to monitor experimentally. It is usually joined to a regulatory sequence, which will then switch on the reporter gene in the normal context in which its own gene is usually expressed
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Repressor
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A protein that binds to a specific regulatory region of DNA to prevent transcription of an adjacent gene
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Ribosomal RNA (rRNA)
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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
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Ribosomes
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Particle composed of ribosomal RNAs and ribosomal proteins that associates with messenger RNA and catalyzes the synthesis of protein
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Riboswitch
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Short sequences within some RNAs that change their conformation when specifically bound to small molecules such as metabolites and in this way regulate transcription or translation
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Ribozyme
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An RNA molecule possessing catalytic properties
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RNA
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A (usually) single-stranded polynucleotide in the form of a chain of covalently linked ribonucleotide subunits. It is synthesized when an RNA polymerase copies the nucleotide sequence of DNA. RNA serves a variety of functions in cells.
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RNA Interference (RNAi)
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Cellular mechanism activated by double-stranded RNA molecules that results in the destruction of RNAs containing a similar nucleaotide sequence. It is widely exploited as an experimental tool for preventing the expression of selected genes (gene silencing)
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RNA Polymerase
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Enzyme that catalyzes the synthesis of an RNA molecule on a DNA template from nucleoside triphosphate precursors
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Rough Endoplasmic Reticulum
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Region of the ER associated with ribosomes and involved in the synthesis of secreted and membrane-bound proteins
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Second Messenger
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Small molecule formed in or released into the cytosol in response to an extracellular signal that helps to relay the signal to the interior of the cell
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Secondary Structure
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Regular local folding pattern of a polymeric molecule in proteins, it refers to alpha helices and beta sheets
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Secretory Vesicle
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Membrane-enclosed organelle in which molecules destined for secretion are stored prior to release. Sometimes called a secretory granule because darkly staining contents make the organelle visible as a small solid object
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Sequence Identity
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The linear order of monomers in a large molecule, for eample amino acids in a protein or nucleotides in DNA. In general the sequence of a macromolecule specifies its precise biological information.
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Serine/Threonine Kinase
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Enzyme that phosphorylates specific proteins on serines or thronines
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Side Chain
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Portion of an amino acid not involved in making peptide bonds; gives each amino acid its unique properties
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Signal Cascade
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Sequence of linked protein reactions, often including phosphorylation and dephosphorylation, that carries information within a cell, often amplifying an initial signal
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Signal Sequence
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Amino acid sequence that directs a protein to a specific location in the cell, such as the nucleus or mitochondria
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Signal Transduction
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Conversion of an impulse or stimulus from one physical or chemical form to another. The process by which a cell responds to an extracellular signal
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Small Interfering RNA (siRNA)
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Short lengths of RNA produced from double-stranded RNA during the process of RNA interference. They base-pair with identical sequences in other RNAs, leading to the inactivation or destruction of the target RNA
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Small Messenger
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Small molecule formed in or released into the cytosol in response to an extracellular signal that helps to relay the signal to the interior of the cell (second messenger)
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SNARE
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One of a family of membrane proteins responsible for the selective fusion of vesicles with a target membrane inside the cell
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Sodium-Potassium Pump
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Transmembrane carrier protein, found in the plasma membrane of most animal cells, that pumps Na+ out of and K+ into cell, using the energy derived from ATP hydrolysis
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Specificity
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Selective affinity of one molecule for another that permits the two to bind or react, even in the presence of many unrelated molecular species
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Spectrin
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Cytoskelital protein that lines the inner side of the plasma membrane
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Stem Cell
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Relatively undifferentiated cell that can continue dividing indefinitely, throwing off daughter cells that undergo terminal differentiation into particular cell types
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Steroid Hormone
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Lipophilic molecule related to cholesterol that acts as a hormone. Estrogen ; testosterone as examples
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Storage Protein
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Biological reserve of metal ions and amino acids; used by organisms
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Telomere
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Structure at the ends of linear chromosomes, associated with a characteristic DNA sequence that is replicated in a pecial way. Counteracts the tendency of the chromosome otherwise to shorten with each round of replication.
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Transcription Factor
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Term loosely applied to any protein required to initieate or regulate transcription in eucaryotes. Includes transcription regulators as well.
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Transcription Promoter
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Region of DNA that facilitates the transcription of a particular gene
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Transcription Regulator
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Protein that binds specifically to a regulatory DNA sequence and is involved in controlling whether a gene is switched on or off
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Transcription Terminator
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Region of DNA that markes the end of the transcription of a particular gene
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Transfer RNA (tRNA)
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Set of small RNA molecules used in protein synthesis as an interface (adaptor) between mRNA and amino acids. Each type of this molecule is covalently linked to a particular amino acid.
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Transport Protein
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Protein that carries ions, small molecules or macromolecules across a biological membrane
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Transport Vesicle
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Membrane vesicles that carry proteins from one intracellular compartment to another, for example from the ER to the Golgi
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Transporter
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Membrane protein that transports ions or molecules across a cell membrane
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Tyrosine Kinase
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Enzyme that phosphorylates specific proteins on tyrosines
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Ubiquitin
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Directs proteins to the proteasome, which is an organelle in the cell that degrades and recycles unneeded proteins
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Unfolded Protein Response (URP)
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Cellular response triggered by the accumulation of misfolded proteins in the ER. The cell produces more ER and more of the molecular machinery needed to restore proper protein folding and processing
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Vesicle
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Small, membrane-enclosed, spherical organelle in the cytoplasm of a eucaryotic cell
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Vesicle Fusion
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The merging of a vesicle with another vesicle or a part of a cell membrane
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Vesicular Transport
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Transport of material between organelles in the eukaryotic cell via membrane-enclosed vesicles
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Voltage-Gated Channel
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Membrane protein that selectively allows ions such as sodium to cross a membrane and is opened by changes in membrane potential. Found mainly in electrically excitable cells such as nerve and muscle.
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X-Ray Crystallography
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Technique used to determine three-dimensional protein structures by analyzing the diffraction pattern of a beam of X-rays passed through a crystal of the protein.

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