Cyclic AMP (cAMP)
A nucleotide generated from ATP by adenylyl cyclase in response to various extracellular signals that acts as a small intracellular signalling molecule, mainly by activating cAMP-dependent protein kinase (PKA); hydrolyzed to AMP by a phosphodiesterase.
ARP (actin-related protein) complex (Arp 2/3 complex)
A complex of proteins that nucleates actin filament growth from the minus end.
An extracellular signal molecule that stimulates cells to proliferate.
A type of endocytosis in which soluble materials are continually taken up from the environment in small vesicles and moved into endosomes along with the membrane-bound molecules.
A plant or animal that has stably incorporated one or more genes from another cell or organism (through insertion, deletion, and/or replacement) and can pass them on to successive generations.
A tumour at the original site at which a cancer first arose; secondary tumours develop elsewhere by metastasis.
Protein tyrosine phosphatase
An enzyme that removes phosphate groups from phosphorylated tyrosine residues on proteins.
A hairlike extension of a eukaryotic cell containing a core bundle of microtubules; many cells contain a single nonmotile cilium, while others contain large numbers that perform repeated beating movements.
A cell-cell junction that seals adjacent epithelial cells together, preventing the passage of most dissolved molecules from one side of the epithelial sheet to the other.
The maternal and paternal copies of a particular chromosome.
A member of a family of secreted signal proteins that have many different roles in controlling cell differentiation, proliferation, and gene expression in animal embryos and adult tissues.
The process by which a cell undergoes a change to an overtly specialized cell type.
Regulation by a cell of gene expression by selecting which mRNAs in the cytoplasm are translated by ribosomes.
A large family of membrane transport proteins that use energy from ATP hydrolysis to transfer peptides or small molecules across membranes.
A large protein kinase involved in mammalian cell signalling.
Single-pass transmembrane protein
A membrane protein in which the polypeptide chain crosses the lipid bilayer only once.
An artificial phospholipid bilayer vesicle formed from an aqueous suspension of phospholipid molecules.
A type of protease that has a reactive serine in the active site.
γ-tubulin ring complex (γ-TuRC)
A protein complex containing γ-tubulin and other proteins that is an efficient nucleator of microtubules and caps their minus ends.
A signalling pathway activated by binding of a Wnt protein to its cell-surface receptors, resulting in increased amounts of β-catenin entering the nucleus to regulate the transcription of genes controlling cell differentiation and proliferation; overactivation of the Wnt/β-catenin pathway can lead to cancer.
A lipid containing a phosphorylated inositol derivative; a minor component of the plasma membrane, but important in demarking different membranes and for intracellular signal transduction in eukaryotic cells.
An intracellular protease that is involved in mediating the intracellular events of apoptosis.
Mitochondrial precursor proteins
Proteins first fully synthesized in the cytosol and then translocated into mitochondrial subcompartments as directed by 1 or more signal sequences.
A complex of proteins that holds sister chromatids together along their length before separation.
Nuclear localization signal (NLS)
A signal sequence or signal patch found in proteins destined for the nucleus that enables their selective transport into the nucleus from the cytosol through the nuclear pore complexes.
The process by which early endosomes mature to late endosomes and endolysosomes: the endosome membrane protein composition changes, the endosome moves from the cell periphery closer to the nucleus, and the endosome ceases to recycle to the plasma membrane and irreversibly commits its remaining contents to degradation.
A protein kinase that inhibits Cdk activity by phosphorylating amino acids in the Cdk active site; important in regulating entry into M phase of the cell cycle.
Receptor serine/threonine kinase
A cell-surface receptor with an extracellular ligand-binding domain and an intracellular kinase domain that phosphorylates signalling proteins on serine or threonine residues in response to ligand binding.
The combined influence of a difference in the concentration of an ion on 2 sides of a membrane and the electrical charge difference across the membrane (membrane potential); ions or charged molecules can move passively only down their electrochemical gradient.
G protein (trimeric GTP-binding protein)
A trimeric GTP-binding protein with intrinsic GTPase activity that couples GPCRs to enzymes or ion channels in the plasma membrane.
The uptake of material into a cell by an invagination of the plasma membrane and its internalization in a membrane-enclosed vesicle.
A large array of short DNA molecules, each of known sequence, bound to a glass microscope slide or other support, used to monitor expression of thousands of genes simultaneously: mRNA isolated from test cells is converted to cDNA, which in turn is hybridized to the microarray.
Genes or proteins that are similar in sequence because they are the result of a gene duplication event occurring in an ancestral organism; those in two different organisms are less likely to have the same function than are orthologs.
A segment of a eukaryotic gene that consists of a sequence of nucleotides that will be represented in mRNA or in a final transfer, ribosomal, or other mature RNA molecule; in protein-coding genes, exons encode the animo acids in the protein.
Voltage-gated K+ channel
An ion channel in the membrane of nerve cells that opens in response to membrane depolarization, enabling K+ efflux and rapid restoration of the negative membrane potential.
A bipolar array of microtubules and associated molecules that forms in a eukaryotic cell during mitosis and serves to move the duplicated chromosomes apart.
Nuclear export receptors
Receptor proteins that bind to both the export signal and nuclear pore complex proteins to guide their cargo through the NPC into the cytosol.
A protein-binding domain present in many scaffold proteins and often used as a docking site for intracellular tails of transmembrane proteins.
A channel protein embedded in the plasma membrane that greatly increases the cell's permeability to water, allowing transport of water, but not ions, at a high rate across the membrane.
A heritable change in the nucleotide sequence of a chromosome.
Single-strand DNA-binding (SSB) protein
A protein that binds to the single strands of the opened-up DNA double helix, preventing helical structures from reforming while the DNA is being replicated.
The period of a eukaryotic cell cycle in which DNA is synthesized.
Conservative site-specific recombination
A type of DNA recombination that takes place between short, specific sequences of DNA and occurs without the gain or loss of nucleotides; does not require extensive homology between the recombining DNA molecules.
High-performance liquid chromatography (HPLC)
A type of chromatography that uses columns packed with tiny beads of matrix; the solution to be separated is pushed through under high pressure.
A transmembrane receptor protein (and latent transcription regulator) involved in many cell-fate choices in animal development; its ligands are cell-surface proteins such as Delta and Serrate.
Part of a multisubunit protein assembly bound to the matrix side of the TIM23 complex that acts as a motor to pull mitochondrial precursor proteins into the matrix space.
Secondary tumours, at sites in the body additional to that of the primary tumour, resulting from cancer cells breaking loose, entering blood or lymphatic vessels, and colonizing separate environments.
A highly condensed duplicated chromosome as seen at mitosis, consisting of 2 sister chromatids held together at the centromere.
Fluorescence resonance energy transfer (FRET)
A technique for monitoring the closeness of 2 fluorescently labelled molecules (and thus their interaction) in cells.
A small membrane-enclosed organelle with a cage of proteins (the coat) on its cytosolic surface, formed by the pinching off of a coated region of membrane (coated pit); some coats are made of clathrin, while others are made from other proteins (e.g. COPI, COPII).
Horizontal gene transfer
Gene transfer between bacteria via natural transformation or by released naked DNA, transduction by bacteriophages, or sexual exchange by conjugation.
Cancer of white blood cells.
CRE-binding (CREB) protein
A transcription regulator that recognizes the cAMP response element (CRE) in the regulatory region of genes activated by cAMP; on activation by PKA, phosphorylated CREB recruits a transcriptional coactivator (CBP) to stimulate transcription of target genes.
Pleckstrin homology (PH) domain
A protein domain found in some intracellular signalling proteins; some PH domains in intracellular signalling proteins bind to PI(3,4,5)P3 produced by PI 3-kinase, bringing the signalling protein to the plasma membrane when PI 3-kinase is activated.
A short continuous sequence of amino acids that determines the eventual location of a protein in the cell.
A large protein complex that connects the centromere of a chromosome to microtubules of the mitotic spindle.
Cancer of epithelial cells; the most common form of human cancer.
A process in bacteria and mitochondria in which ATP formation is driven by the transfer of electrons through the electron-transport chain to molecular oxygen; involves the intermediate generation of a proton gradient across a membrane and a chemiosmotic coupling of that gradient to the ATP synthase.
Proteins that attach to specific membrane regions as needed and act to control local membrane curvature and thus confer on membranes their characteristic 3D shapes.
A transcription regulatory protein that is activated when a cell is stimulated to grow and divide by extracellular signals; it activates the transcription of many genes, including those that stimulate cell growth.
Microtubule-associated protein (MAP)
Any protein that binds to microtubules and modifies their properties, including structural and motor proteins.
Bcl2 family proteins produced or activated in response to an apoptotic stimulus that promote apoptosis mainly by inhibiting anti-apoptotic Bcl2 family proteins; the largest subclass of Bcl2 family proteins.
A multifunctional Ca2+/calmodulin-dependent protein kinase that phosphorylates itself and various target proteins when activated; found in most animal cells but is especially abundant in the brain, and is involved in some forms of memory and learning in vertebrates.
A protein that binds groups of intracellular signalling proteins into a signalling complex, often anchoring the complex at a specific location in the cell.
A transmembrane receptor protein that can signal the cell to undergo apoptosis when it binds its extracellular ligand (e.g. Ras).
An organ containing large numbers of lymphocytes; lymphocytes are produced in primary lymphoid organs and respond to antigen in peripheral lymphoid organs.
A serine/threonine protein kinase that acts in the PI 3-kinase/Akt intracellular signalling pathway involved in signalling cells to grow and survive.
An anti-apoptotic Bcl2 family protein of the outer mitochondrial membrane that binds and inhibits pro-apoptotic Bcl2 family proteins and prevents inappropriate activation of the intrinsic pathway of apoptosis.
ER resident protein
A protein that remains in the ER or its membranes and carries out its function there, as opposed to proteins that are present in the ER only in transit.
Single-nucleotide polymorphism (SNP)
A variation between individuals in a population due to a relatively common difference in a specific nucleotide at a defined point in the DNA sequence.
An ordered recruitment of sequentially acting Rab proteins into Rab domains on membranes, which changes the identity of an organelle and reassigns membrane dynamics.
A small, circular molecule of double-stranded DNA derived from plasmids that occur naturally in bacterial cells; widely used for gene cloning.
The process of transferring a single saccharide or preformed precursor oligosaccharide to proteins.
A protein essential in the preparation of DNA for replication: with Cdt1 it binds to an origin recognition complex (ORC) on chromosomal DNA and helps load the Mcm helicases onto the complex to form the prereplicative complex (preRC).
A small family of proto-oncogenes that are frequently mutated in cancers, each of which produces a Ras monomeric GTPase.
A type of intermediate filament commonly produced by epithelial cells.
An extracellular signal molecule that acts on neighbouring cells.
The process by which each muscle cell at first receives synapses from several motor neurons, but is ultimately left innervated by only one.
A computational procedure in electron microscopy in which images of many identical molecules are obtained and digitally combined to produce an averaged 3D image, thereby revealing structural details that are hidden by noise in the original images.
An enzyme that binds to DNA and reversibly breaks a phosphodiester bond in 1 or both strands: topoisomerase I creates transient single-strand breaks, allowing the double helix to swivel and relieving superhelical tension; topoisomerase II creates transient double-strand breaks, allowing 1 double helix to pass through another and thus resolving tangles.
A cell with an altered phenotype that behaves in many ways like a cancer cell (i.e. unregulated proliferation, anchorage-independent growth in culture).
Inhibitory G protein (Gi)
A trimeric G protein that can regulate ion channels and inhibit the enzyme adenylyl cyclase in the plasma membrane.
Bacterial artificial chromosome (BAC)
A cloning vector that can accommodate large pieces of DNA, typically up to 1 million base pairs.
A membrane transport protein that binds to a solute and transports it across the membrane by undergoing a series of conformational changes; they can transport ions or molecules passively down an electrochemical gradient or can link the conformational changes to a source of metabolic energy such as ATP hydrolysis to drive active transport.
A control mechanism whereby the end product of a reaction or pathway stimulates its own production or activation.
An extension of a nerve cell, often elaborately branched, that receives stimuli from other nerve cells.
The movement of a cell toward or away from some diffusible chemical.
An ER-resident chaperone protein and member of the family of hsp70-type chaperone proteins.
Janus kinases (JAKs)
Cytoplasmic tyrosine kinases associated with cytokine receptors, which phosphorylate and activate transcription regulators called STATs.
The retention by cells and their descendants of persistently altered patterns of gene expression, without any change in DNA sequence (epigenetic inheritance).
Cyclic AMP phosphodiesterase
A specific enzyme that rapidly and continuously destroys cAMP, forming 5'-AMP.
A secreted extracellular signal molecule that has many different roles controlling cell differentiation and gene expression in animal embryos and adult tissues; excessive Hedgehog signalling can lead to cancer.
In the mitotic spindle, any of the microtubules radiating from the aster which are not attached to a kinetochore of a chromosome.
Electron microscope (EM) tomography
A technique for viewing 3D specimens in the electron microscope in which multiple views are taken from different directions by tilting the specimen holder; the views are combined computationally to give a 3D image.
An adaptor protein of the intrinsic apoptotic pathway; on binding cytochrome c, it oligomerizes to form an apoptosome.
A tightly linked pair of chromosomes that arise from chromosome duplication during S phase; they separate during M phase and segregate into different daughter cells.
A ligand that activates the cell-surface death receptor Fas, triggering the extrinsic pathway of apoptosis.
Multidrug resistance (MDR) protein
A type of ABC transporter protein that can pump hydrophobic drugs (such as some anticancer drugs) out of the cytoplasm of eukaryotic cells.
A transcription regulatory protein that is activated by damage to DNA and is involved in blocking further progression through the cell cycle.
1 of a group of small abundant proteins, rich in Arg and Lys, that combine to form the nucleosome cores around which DNA is wrapped in eukaryotic chromosomes.
Cancer of connective tissue.
Purified cell-free system
A fractionated cell homogenate that retains a particular biological function of the intact cell, and in which biochemical reactions and cell processes can be more easily studied.
A common folding pattern in proteins, in which a linear sequence of amino acids folds into a right-handed helix stabilized by internal H-bonding between backbone atoms.
ER tail-anchored proteins
Membrane proteins anchored in the ER membrane by a single transmembrane alpha helix contained at their C-terminus.
A protein essential in the preparation of DNA for replication: with Cdc6 it binds to origin recognition complexes (ORCs) on chromosomes and helps load the Mcm helicases on to the complex, forming the prereplicative complex (preRC).
A complex of DNA, histones, and non-histone proteins found in the nucleus of a eukaryotic cell; the material of which chromosomes are made.
Protein kinase C (PKC)
A Ca2+-dependent protein kinase that, when activated by diacylglycerol and an increase in cytosolic [Ca2+], phosphorylates target proteins on specific serine and threonine residues.
A clathrin-independent, dedicated degradative endocytic pathway induced in most cell types by cell-surface receptor activation by specific cargoes.
A large intracellular membrane-enclosed vesicle that is formed as a result of phagocytosis; contains ingested extracellular material.
A type of light microscopy in which oblique rays of light focused on the specimen do not enter the objective lens, but light that is scattered by components in the living cell can be collected to produce a bright image on a dark background.
cAMP-dependent protein kinase (PKA)
An enzyme that phosphorylates target proteins in response to a rise in intracellular cAMP.
A small vesicle derived from ER that is produced by fragmentation when cells are homogenized.
A flattened, sheetlike protrusion supported by a meshwork of actin filaments, which is extended at the leading edge of a crawling animal cell.
The final stage of mitosis, in which the two sets of separated chromosomes decondense and become enclosed by nuclear envelopes.
An enzyme that synthesizes DNA by joining nucleotides together using a DNA template as a guide.
The long period of the cell cycle between 1 mitosis and the next; includes G1, S, and G2.
STAT (signal transducer and activator of transcription)
A latent transcription regulator that is activated by phosphorylation by JAKs and enters the nucleus in response to signalling from receptors of the cytokine receptor family.
A white blood cell responsible for the specificity of adaptive immune responses; includes B cells (produce antibodies) and T cells (interact with other immune cells and with infected cells).
An ion channel found at chemical synapses in the postsynaptic plasma membranes of nerve and muscle cells that opens only in response to the binding of a specific extracellular neurotransmitter; the resulting inflow of ions leads to the generation of a local electrical signal in the postsynaptic cell.
A bundle of microtubules and associated proteins that forms the core of a cilium or a flagellum in eukaryotic cells and is responsible for their movements.
Cytoplasmic tyrosine kinase
An enzyme activated by certain cell-surface receptors (tyrosine-kinase-associated receptors) that transmits the receptor signal onward by phosphorylating target cytoplasmic proteins on tyrosine side chains.
Gap 1 phase of the eukaryotic cell cycle, between the end of mitosis and the start of DNA synthesis.
Copy number variations (CNVs)
A difference between 2 individuals in the same population in the number of copies of a particular block of DNA sequence; this variation arises from occasional duplications and deletions of these sequences.
Molecules that bind activated, membrane-bound Rab proteins and act as downstream mediators of vesicle transport, membrane tethering, and fusion.
A transmembrane adhesion protein that is involved in the attachment of cells to the extracellular matrix and to each other.
A specialized chemical synapse between an axon terminal of a motor neuron and a skeletal muscle cell.
GTPase-activating protein (GAP)
A protein that binds to a GTPase and inhibits it by stimulating its GTPase activity, causing the enzyme to hydrolyze its bound GTP to GDP.
The movement of individual tubulin molecules in the microtubules of the spindle toward the poles by loss of tubulin at their minus ends; helps to generate the poleward movement of sister chromatids after they separate in anaphase.
A family of monomeric GTPases within the Ras superfamily involved in signalling the rearrangment of the cytoskeleton; includes Rho, Rac, and Cdc42.
Prereplicative complex (preRC)
A multiprotein complex that is assembled at origins of replication during late mitosis and early G1 phases of the cell cycle; a prerequisite to license the assembly of a preinitiation complex, and the subsequent initiation of DNA replication.
Base excision repair
A DNA repair pathway in which single faulty bases are removed from the DNA helix and replaced.
Any one of a large number of enzymes that attach ubiquitin to a protein, often marking it for destruction in a proteasome.
An activating subunit of the anaphase-promoting complex (APC/C).
A small region of a membrane enriched in sphingolipids and cholesterol.
A thin mat of extracellular matrix that separates epithelial sheets, and many other types of cells such as muscle or fat cells, from connective tissue.
A transmembrane protein complex that forms a water-filled channel across the lipid bilayer through which specific inorganic ions can diffuse down their electrochemical gradients.
A protein phosphatase that dephosphorylates Cdks and increases their activity.
A type of light microscope that exploits the interference effects that occur when light passes through parts of a cell of different refractive indices; used to view unstained living cells.
The part of an ion channel structure that determines which ions it can transport.
An enzyme that elongates telomere sequences in DNA, which occur at the ends of eukaryotic chromosomes.
A dimeric protein that nucleates the growth of straight, unbranched actin filaments that can be cross-linked by other proteins to form parallel bundles.
Of tumours and tumour cells: invasive and/or able to undergo metastasis; a malignant tumour is a cancer.
A class of ATP-driven pumps comprising structurally and functionally related multipass transmembrane proteins that phosphorylate themselves during the pumping cycle; includes many of the ion pumps responsible for setting up and maintaining gradients of Na+, K+, H+, and Ca2+ across cell membranes.
A rapid, transient, self-propagating electrical excitation int he plasma membrane of a cell such as a neuron or muscle cell; allows long-distance signalling in the nervous system.
Induced pluripotent stem cells (iPS cells)
Cells that are induced by artificial expression of specific transcription regulators to look and behave like the pluripotent embryonic stem cells that are derived from embryos.
A thin, spike-like protrusion with an actin filament core, generated on the leading edge of a crawling animal cell.
A type of motor protein that uses the energy of ATP hydrolysis to move along actin filaments.
A developmental process in which cells undergo movements and deformations in order to assemble into tissues and organs with specific shapes and sizes.
A single-pass transmembrane signal protein displayed on the surface of cells that binds to the Notch receptor protein on a neighbouring cell, activating a contact-dependent signalling mechanism.
The protein subunit of microtubules.
A cyclin present in the G1 phase of the eukaryotic cell cycle; forms complexes with Cdks that help govern the activity of the G1/S cyclins, which control progression to S phase.
An antibody secreted by a hybridoma cell line; because the hybridoma is generated by the fusion of a single B cell with a single tumour cell, each hybridoma produces antibodies that are all identical.
Cell-cycle control system
A network of regulatory proteins that governs progression of a eukaryotic cell through the cell cycle.
The spread of cancer cells from their site of origin to other sites in the body.
A carrier protein that transports 2 different ions or small molecules across a membrane in opposite directions, either simultaneously or in sequence.
Occurring after completion of translation.
Limit of resolution
In microscopy, the smallest distance apart at which 2 point objects can be resolved as separate; just under 0.2 μm for conventional light microscopy, a limit determined by the wavelength of light.
Coated vesicles that transport material early in the secretory pathway, budding from Golgi compartments.
Neuron (nerve cell)
An impulse-conducting cell of the nervous system, with extensive processes specialized to receive, conduct, and transmit signals.
Vesicle transport model
One hypothesis for how the Golgi achieves and maintains its polarized structure and how molecules move from one cisterna to another: this model holds that Golgi cisternae are long-lived structures that retain their characteristic set of Golgi-resident proteins firmly in place, and cargo proteins are transported from one cisterna to the next by transport vesicles.
GTPases consisting of a single subunit that help relay signals from many types of cell-surface receptors and have roles in intracellular signalling pathways, regulating intracellular vesicle traffic, and signalling to the cytoskeleton; frequently act as molecular switches in intracellular signalling pathways.
A cell-surface receptor that binds a specific cytokine or hormone and acts through the JAK-STAT signalling pathway.
A diffusible signal molecule that can impose a pattern on a field of cells by causing cells in different places to adopt different fates.
Consensus nucleotide sequence
A summary or "average" of a large number of individual nucleotide sequences derived by comparing many sequences with the same basic function and tallying up the most common nucleotides found at each position.
A member of the Rho family of monomeric GTPases that regulate the actin and microtubule cytoskeletons, cell-cycle progression, gene transcription, and membrane transport.
A neurotransmitter that opens cation channels in the postsynaptic membrane, causing an influx of Na+, and in many cases Ca2+, that depolarizes the postsynaptic membrane toward the threshold potential for firing an action potential.
The addition of methyl groups to DNA; extensive methylation of the cytosine base in CG sequences is used in plants and animals to help keep genes in an inactive state.
A microscope designed to view material stained with fluorescent dyes or proteins; similar to a light microscope, but the illuminating light is passed through 1 set of filters before the specimen, to select those wavelengths that excite the dye, and through another set of filters before it reaches the eye, to select only those wavelengths emitted when the dye fluoresces.
Monomeric GTPases in the Ras superfamily responsible for regulating both COPI coat assembly and clathrin coat assembly.
A cell derived from a stem cell that divides for a limited number of times before terminally differentiating.
Apoptotic caspases that catalyze the widespread cleavage events during apoptosis that kill the cell.
A multisubunit protein complex that transports proteins across the mitochondrial outer membrane.
Membrane-enclosed transport containers that bud from specialized coated regions of donor membrane and pass from one cell compartment to another as part of the cell's membrane transport processes; vesicles can be spherical, tubular, or irregularly shaped.
Resting membrane potential
The electrical potential across the plasma membrane of a cell at rest, i.e. a cell that has not been stimulated to open additional ion channels than those that are normally open.
Cdk inhibitor protein (CKI)
A protein that binds to and inhibits cyclin-Cdk complexes, primarily involved in the control of G1 and S phases.
Focal adhesion kinase (FAK)
A cytoplasmic tyrosine kinase present at cell-matrix junctions (focal adhesions) in association with the cytoplasmic tails of integrins.
A sequence of 3 nucleotides in a DNA or mRNA molecule that represents the instruction for incorporation of a specific amino acid into a growing polypeptide chain.
A virus that can help make the cell it infects cancerous.
A common structural motif in proteins in which different sections of the polypeptide chain run alongside each other, joined together by H-bonding between atoms of the polypeptide backbone.
A protein that prevents the formation of new prereplicative complexes (preRCs) during S phase and mitosis, thus ensuring that the chromosomes are replicated only once in each cell cycle.
Protein complexes in the mitochondrial inner membrane: TIM23 mediates the transport of proteins into the matrix and the insertion of some proteins into the inner membrane; TIM22 mediates the insertion of a subgroup of proteins into the inner membrane.
Intermediates in the endosome maturation process; early endosomes that are on their way to becoming late endosomes.
Any cell of a plant or animal other than cells of the germ line.
A cell junction in which the cytoplasmic face of the plasma membrane is attached to actin filaments (e.g. adhesion belts linking adjacent epithelial cells; focal contacts on the lower surface of cultured fibroblasts).
A small intracellular signalling molecule that is formed or released for action in response to an extracellular signal and helps to relay the signal within the cell; examples include cAMP, IP3, Ca2+, and diacylglycerol.
A transcription regulatory protein that switches on many genes that encode proteins required for entry into the S phase of the cell cycle.
A rare type of human cancer arising from cells in the retina of the eye that are converted to a cancerous state by an unusually small number of mutations.
In molecular biology, the process whereby 2 complementary nucleic acid strands form a base-paired duplex DNA-DNA, DNA-RNA, or RNA-RNA molecule; forms the basis of a powerful technique for detecting specific nucleotide sequences.
The point in the eukaryotic cell cycle at which the cell checks for completion of DNA replication before triggering the early mitotic events that lead to chromosome alignment on the spindle.
The location on a DNA molecule at which duplication of the DNA begins.
Voltage-gated Na+ channel
An ion channel in the membrane of nerve and skeletal muscle cells that opens in response to a stimulus causing sufficient depolarization, allowing Na+ to enter the cell down its electrochemical gradient.
A membrane phosphoinositide that is cleaved by phospholipase C into IP3 and diacylglycerol at the beginning of the inositol phospholipid signalling pathway; it can also be phosphorylated by PI 3-kinase to produce PI(3,4,5)P3 docking sites for signalling proteins in the PI-3-kinase-Akt signalling pathway.
A molecule consisting of 1 or more glycosaminoglycan chains attached to a core protein.
Spindle assembly checkpoint
A regulatory system that operates during mitosis to ensure that all chromosomes are properly attached to the spindle before sister-chromatid separation starts.
A water-filled pore in the plasma membrane formed by a ring of 6 connexin protein subunits; half of a gap junction: connexons from 2 adjoining cells join to form a continuous channel through which ions and small molecules can pass.
Any protein with 1 or more saccharide or oligosaccharide chains covalently linked to amino acid side chains; most secreted proteins and most proteins exposed on the outer surface of the plasma membrane are glycoproteins.
A lipid produced by the cleavage of inositol phospholipids in response to extracellular signals; composed of 2 fatty acid chains linked to glycerol, it serves as a small signalling molecule to help activate PKC.
A technique for studying intracellular processes in which an inactive form of a molecule of interest is introduced into the cell, and is then activated by a focused beam of light at a precise spot in the cell.
A 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.
A nucleotide sequence in DNA to which RNA polymerase binds to begin transcription.
Ras-MAP-kinase signalling pathway
An intracellular signalling pathway that relays signals from activated receptor tyrosine kinases to effector proteins in the cell, including transcription regulators in the nucleus.
Rapidly inactivating K+ channel
A neuronal voltage-gated K+ channel, open when the membrane is depolarized, with a specific voltage sensitivity and kinetics of inactivation that induce a reduced rate of action potential firing at levels of stimulation only just above the threshold required, thereby resulting in a firing rate proportional to the strength of the depolarizing stimulus.
A class of viruses responsible for human warts and a prime example of DNA tumour viruses, being a cause of cancer of the uterine cervix.
In cancer, one or more detectable abnormalities in the DNA sequence of tumour cells that distinguish them from the normal somatic cells surrounding the tumour.
A long nerve cell projection that can rapidly conduct nerve impulses over long distances to deliver signals to other cells.
A major type of cell-surface receptor that has a cytoplasmic domain that either has enzymatic activity or is associated with an intracellular enzyme; in either case, the enzymatic activity is stimulated by an extracellular ligand binding to the receptor.
Describes several approaches in light microscopy that bypass the limit imposed by the diffraction of light and successfully allow objects as small as 20 nm to be imaged and clearly resolved.
A region of DNA in vertebrate genomes with a greater than average density of CG sequences; these regions generally remain unmethylated.
Internalization of receptor-ligand complexes from the plasma membrane by endocytosis.
Phospholipase C (PLC)
A membrane-bound enzyme that cleaves inositol phospholipids to produce IP3 and diacylglycerol in the inositol phospholipid signalling pathway; PLC-β is activated by GPCRs via specific G proteins, while PLC-γ is activated by RTKs.
A form of programmed cell death, in which a "suicide" program is activated within an animal cell, leading to rapid cell death mediated by intracellular proteolytic enzymes called caspases.
The 3-subunit core of the protein translocator that transfers polypeptide chains across the ER membrane.
Stimulatory G protein (Gs)
A G protein that, when activated, activates the enzyme adenylyl cyclase and thus stimulates the production of cAMP.
A protein that functions solely to link 2 or more different proteins together in an intracellular signalling pathway or protein complex.
Apoptotic caspases that begin the apoptotic process, activating the executioner caspases.
Nuclear transport receptor
A protein that escorts macromolecules into or out of the nucleus.
Monomeric GTPases in the Ras superfamily present in plasma and organelle membranes in their GTP-bound state, and as soluble cytosolic proteins in their GDP-bound state; involved in conferring specificity on vesicle docking.
A short amino acid sequence that enables a polypeptide chain to start being translocated across the ER membrane through a protein translocator; multipass membrane proteins sometimes have both N-terminal (signal sequence) and internal start-transfer signals.
A main effector Bcl2 family protein of the intrinsic pathway of apoptosis in mammalian cells; located mainly in the cytosol and translocates to the mitochondria only after activation, usually by activated pro-apoptotic BH3-only proteins.
An extracellular signal protein that can stimulate a cell to grow; they often have other functions as well, including stimulating cells to survive or proliferate.
JAK-STAT signalling pathway
A signalling pathway activated by cytokines and some hormones, providing a rapid route from the plasma membrane to the nucleus to alter gene transcription; involves cytoplasmic Janus kinases (JAKs) and signal transducers and activators of transcription (STATs).
Any molecule that binds to a specific site on a protein or other molecule.
SNARE proteins (SNAREs)
Members of a large family of transmembrane proteins present in organelle membranes and the vesicles derived from them that catalyze membrane fusion events in cells; they exist in pairs (a v-SNARE in the vesicle membrane that binds specifically to a complementary t-SNARE in the target membrane).
Microtubule-organizing centre (MTOC)
A region in a cell, such as a centrosome or a basal body, from which microtubules grow.
A carbohydrate-binding chaperone protein in the ER lumen that binds to oligosaccharides on incompletely folded proteins and retains them in the ER.
Cyclin-dependent kinase (Cdk)
A protein kinase that has to be complexed with a cyclin protein in order to act; different cyclin-Cdk complexes trigger different steps in the cell cycle by phosphorylating specific target proteins.
Cisternal maturation model
1 hypothesis for how the Golgi achieves and maintains its polarized structure and how molecules move from 1 cisterna to another: this model views the cisternae as dynamic structures that mature from early to late by acquiring and then losing specific Golgi-resident proteins as they move through the Golgi stack with cargo.
A broad class of N-linked oligosaccharides, attached to mammalian glycoproteins in the ER and modified in the Golgi, containing N-acetylglucosamine, galactose, sialic acid, and fucose residues.
An especially stable rodlike protein structure formed by 2 or more alpha helices coiled around each other.
Inhibitors of apoptosis (IAPs)
Intracellular protein inhibitors of apoptosis.
Anti-apoptotic Bcl2 family proteins
Proteins on the cytosolic surface of the outer mitoichondrial membrane that bind and inhibit pro-apoptotic Bcl2 family proteins and thereby help prevent inappropriate activation of the intrinsic pathway of apoptosis.
A mass of cytoplasm containing many nuclei enclosed by a single plasma membrane; typically the result of either cell fusion or of a series of incomplete division cycles in which the nuclei divide but the cell does not.
Regulation by a cell of gene expression by controlling when and how often a given gene is transcribed.
A short cylindrical array of microtubules; a pair of centrioles is usually found at the centre of a centrosome in animal cells.
A conformation with loops or coils that DNA adopts in response to superhelical tension; conversely, creating various loops or coils in the helix can create such tension.
The pathway of apoptosis triggered by extracellular signal proteins binding to cell-surface death receptors.
Retinoblastoma (Rb) protein
A tumour suppressor protein involved in the regulation of cell division, mutated in the cancer retinoblastoma, as well as in many other tumours; its normal activity is to regulate the eukaryotic cell cycle by binding to and inhibiting the E2F proteins, thus blocking progression to DNA replication and cell division.
A protease that cleaves the cohesin protein linkages that hold sister chromatids together; acts at anaphase, enabling chromatid separation and segregation.
A membrane-enclosed organelle in eukaryotic cells containing digestive enzymes, which are typically most active at the acidic pH found in the lumen of lysosomes.
Cis Golgi network (CGN)
A network of fused vesicular tubular clusters that is closely associated with the cis face of the Golgi apparatus and is the compartment at which proteins and lipids enter the Golgi.
A family of intracellular proteins that either promote or inhibit apoptosis by regulating the release of cytochrome c and other mitochondrial proteins from the intermembrane space into the cytosol.
Regulator of G protein signalling (RGS)
A GAP protein that binds to a trimeric G protein and enhances its GTPase activity, thus helping to limit G-protein-mediated signalling.
Cancer arising from the epithelium lining the colon (large intestine) and rectum (terminal segment of the gut).
Effector Bcl2 family proteins
Pro-apoptotic proteins of the intrinsic pathway of apoptosis that in response to an apoptotic stimulus become activated and aggregate to form oligomers in the mitochondrial outer membrane, inducing the release of cytochrome c and other intermembrane proteins; Bax and Bak are the main effector Bcl2 family proteins in mammalian cells.
The process by which a polymeric actin filament is maintained at constant length by addition of actin subunits at one end and loss of actin subunits at the other.
A protein that assembles into a polyhedral cage on the cytosolic side of a membrane to form a clathrin-coated pit, which buds off by endocytosis to form an intracellular clathrin-coated vesicle.
An undifferentiated cell that can continue dividing indefinitely, throwing off daughter cells that can either commit to differentiation or remain a stem cell (in the process of self-renewal).
Immunogold electron microscopy
A method to localize specific macromolecules using a primary antibody that binds to the molecule of interest and is then detected with a secondary antibody to which a colloidal gold particle has been attached; the gold particle is electron-dense and can be seen as a black dot in the electron microscope.
A protein that helps guide the proper folding of other proteins, or helps them avoid misfolding; includes heat-shock proteins (hsp).
An enzyme that is involved in opening the DNA helix into its single strands for DNA replication.
Endoplasmic reticulum (ER)
A labyrinthine membrane-bounded compartment in the cytoplasm of eukaryotic cells, where lipids are synthesized and membrane-bound proteins and secretory proteins are made.
Cdk-activating kinase (CAK)
A protein kinase that phosphorylates Cdks in cyclin-Cdk complexes, activating the Cdk.
An observed phenomenon in which cells exposed to 1 anticancer drug evolve a resistance not only to that drug, but also to other drugs to which they have never been exposed.
A system of protein filaments in the cytoplasm of a eukaryotic cell that gives the cell shape and the capacity for directed movement; its most abundant components are actin filaments, microtubules, and intermediate filaments.
Any protein that binds to a specific DNA sequence to influence the transcription of a gene.
A class of G protein that couples GPCRs to phospholipase C-β (PLC-β) to activate the inositol phospholipid signalling pathway.
A centrally located organelle of animal cells that is the primary microtubule-organizing centre (MTOC) and acts as the spindle pole during mitosis; in most animal cells, it contains a pair of centrioles.
A hydrophobic amino acid sequence that halts translocation of a polypeptide chain through the ER membrane, thus anchoring the protein in the membrane.
The rate at which changes (mutations) occur in DNA sequences.
A form of intercellular signalling in which signal molecules remain bound to the surface of the signalling cell and influence only cells that contact it.
A type of intermediate filament found in nerve cells.
Green fluorescent protein (GFP)
A fluorescent protein, isolated from a jellyfish, widely used as a marker in cell biology.
GPCR kinase (GRK)
A member of a family of enzymes that phosphorylates multiple serines and threonines on a GPCR to produce receptor desensitization.
A protein translocator in the inner mitochondrial membrane that mediates insertion of inner membrane proteins.
Growth hormone (GH)
A mammalian hormone secreted by the pituitary gland into the bloodstream that stimulates growth throughout the body.
A carbohydrate-binding chaperone protein in the ER membrane that binds to oligosaccharides on incompletely folded proteins and retains them in the ER.
Trans Golgi network
A network of interconnected tubular and cisternal structures closely associated with the trans face of the Golgi and the compartment from which proteins and lipids exit the Golgi, bound for the cell surface or another compartment.
A broad class of N-linked oligosaccharides, attached to mammalian glycoproteins in the ER, containing 2 N-acetylglucosamine residues and many mannose residues.
The limit of cell determination, when a cell forms one of the highly specialized cell types of the adult body.
Anaphase-promoting complex (APC/C; cyclosome)
A ubiquitin ligase that catalyzes the ubiquitylation and destruction of securin and M- and S-cyclins, initiating the separation of sister chromatids in the metaphase-to-anaphase transition during mitosis.
The important transition at the end of G1 in the eukaryotic cell cycle; commits the cell to enter S phase.
A complex of proteins involved in chromosome condensation prior to mitosis; a target for M-Cdk.
A ubiquitous intracellular Ca2+-binding protein that undergoes a large conformational change when it binds Ca2+, allowing it to regulate the activity of many target proteins.
A 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.
IP3-gated Ca2+-release channel (IP3 receptor)
A gated Ca2+ channel in the ER membrane that opens on binding cytosolic IP3, releasing stored Ca2+ into the cytosol.
A cell-surface receptor that functions similarly to RTKs, except that the kinase domain is encoded by a separate gene and is noncovalently associated with the receptor polypeptide chain.
An amphiphilic protein of diverse structure and function that associates with the lipid bilayer of cell membranes.
A normal gene, usually concerned with the regulation of cell proliferation, that can be converted into a cancer-promoting oncogene by mutation.
An enzyme that synthesizes a short strand of RNA on a DNA template, producing a primer for DNA synthesis.
A protein produced in response to various apoptotic stimuli that, by binding to IAPs and preventing their binding to a caspase, neutralizes the inhibition of apoptosis provided by IAPs.
Embryonic stem cells (ES cells)
Cells derived from the inner cell mass of the early mammalian embryo that are capable of giving rise to all the cells in the body; can be grown in culture, genetically modified, and inserted into a blastocyst to develop a transgenic animal.
A transmembrane SNARE protein, usually composed of 3 proteins and found on target membranes, where it interacts with v-SNAREs on vesicle membranes.
Gene control region
The set of linked DNA sequences regulating expression of a particular gene; includes promoter and cis-regulatory sequences required to initiate transcription of the gene and control the rate of transcription.
Hormones, including cortisol, estrogen, and testosterone, that are hydrophobic lipid molecules derived from cholesterol that activate intracellular nuclear receptors.
A specialized animal cell that secretes a hormone into the blood; usually part of a gland, such as the thyroid or pituitary gland.
In the mitotic spindle, a microtubule interdigitating at the equator with the microtubules emanating from the other pole.
Death-inducing signalling complex (DISC)
An activation complex in which initiator caspases interact and are activated following binding of extracellular ligands to cell-surface death receptors in the extrinsic pathway of apoptosis.
The random switching of phenotype and expression of proteins involved in infection at frequencies much higher than mutation rates.
A transposable element that exists as DNA throughout its life cycle; many move by cut-and-paste transposition.
Fluorescence recovery after photobleaching (FRAP)
A technique for monitoring the kinetic parameters of a protein by analyzing how fluorescent protein molecules move into an area of the cell bleached by a beam of laser light.
A ring containing actin and myosin that forms under the surface of animal cells undergoing cell division and contracts to pinch the 2 daughter cells apart.
A technique for separation of a mixture of substances in solution by passage through a column containing a porous solid matrix: substances are retarded to different extents by their interaction with the matrix and can be collected separately from the column; depending on the matrix, separation can be by charge, hydrophobicity, size, or the ability to bind to other molecules.
An electrophysiological technique in which a tiny electrode tip is sealed onto a patch of cell membrane, thereby making it possible to record the flow of current through individual ion channels in the patch.
An RNA molecule that is the final product of a gene and does not code for protein; these RNAs serve as enzymatic, structural, and regulatory components for a wide variety of processes in the cell.
A membrane-bound enzyme that catalyzes the formation of cAMP from ATP; an important component of some intracellular signalling pathways
Membrane transport protein
A membrane protein that mediates the passage of ions or molecules across a membrane; the 2 main classes are transporters and channels.
The process in which a product of a reaction feeds back to inhibit a previous reaction in the same pathway.
Cancer of lymphocytes, in which the cancer cells are mainly found in lymphoid organs (rather than in the blood, as in leukemias).
An enzyme that removes a terminal signal sequence from a protein once the sorting process is complete.
Chromatin that is highly condensed even in interphase; generally transcriptionally inactive.
A structure composed of a very long DNA molecule and associated proteins that carries part (or all) of the hereditary information of an organism; especially evident in plant and animal cells undergoing mitosis or meiosis, during which each chromosome becomes condensed into a compact rodlike structure visible in the light microscope.
Origin recognition complex (ORC)
A large protein complex that is bound to the DNA at origins of replication in eukaryotic chromosomes throughout the cell cycle.
The stage of mitosis during which sister chromatids separate and move away from each other.
A tumour suppressor gene that is mutated in about half of human cancers; encodes a transcription regulator that is activated by damage to DNA and is involved in blocking further progression through the cell cycle.
Intrinsic (mitochondrial) pathway
The pathway of apoptosis activated from inside the cell in response to stress or developmental signals; depends on the release into the cytosol of mitochondrial proteins normally resident in the mitochondrial intermembrane space.
A phospholipid derived from glycerol, abundant in biomembranes.
GPCRs on the modified cilia of olfactory receptor neurons that recognize odors; the receptors activate adenylyl cyclase via an olfactory-specific G protein (Golf) and resultant increases in cAMP open cAMP-gated cation channels, allowing Na+ influx and depolarization and initiation of a nerve impulse.
Ca2+ pump (calcium pump, Ca2+ ATPase)
A transport protein in the membrane of the sarcoplasmic reticulum of muscle cells (and elsewhere) that pumps Ca2+ out of the cytoplasm into the SR lumen using the energy of ATP hydrolysis.
A protein that uses energy derived from ATP or GTP hydrolysis to propel itself along a linear track (protein filament or other polymeric molecule).
A lipid linkage by which some membrane proteins are bound to the membrane; the protein is joined, via an oligosaccharide linker, to a phosphatidylinositol anchor during its travel through the ER.
Ca2+-activated K+ channel
A channel that opens in response to raised [Ca2+] in nerve cells that occurs in response to an action potential; increased K+ permeability makes the membrane harder to depolarize, increasing the delay between action potentials and decreasing the response of the cell to constant, prolonged stimulation (desensitization).
A main effector Bcl2 family protein of the intrinsic pathway of apoptosis in mammalian cells that is bound to the mitochondrial outer membrane, even in the absence of an apoptotic signal; activation is usually by activated pro-apoptotic BH3-only proteins.
The process by which an initial mildly disordered cell behaviour gradually evolves into a full-blown cancer.
The key target of activated Cdc42 that exists in an inactive folded conformation and an activated open conformation; association with Cdc42 stabilizes the open form, enabling binding to the Arp 2/3 complex and enhancing actin-nucleating activity.
Unfolded protein response
A cellular response triggered by an accumulation of misfolded proteins in the ER; involves expansion of the ER and increased transcription of genes that code for ER chaperones and degradative enzymes.
In the mitotic spindle, a microtubule that connects the spindle pole to the kinetochore of a chromosome.
The proposal that all living organisms are composed of 1 or more cells and that all cells arise from the division of other living cells.
An enzyme that catalyzes phosphate removal from amino acids of a target protein.
A hybrid cell line generated by fusion of a tumour cell and another cell type; monoclonal antibodies are produced by hybridoma lines obtained by fusing antibody-secreting B cells with cells of a B lymphocyte tumour.
A cell in the germ line of an organism, which includes the haploid gametes and their specified diploid precursor cells; germ cells contribute to the formation of a new generation of organisms and are distinct from somatic cells, which form the body and leave no descendents.
A cyclin-Cdk complex formed in vertebrate cells by a G1-cyclin and the corresponding Cdk.
A member of the Rho family of monomeric GTPases that regulate the actin and microtubule cytoskeletons, cell-cycle progression, gene transcription, and membrane transport.
The membrane components and soluble molecules carried by transport vesicles.
Inositol phospholipid signalling pathway
An intracellular signalling pathway that starts with activation of phospholipase C and the generation of IP3 and diacylglycerol (DAG) from inositol phospholipids in the plasma membrane; the DAG helps to activate PKC.
Nuclear receptor superfamily
Intracellular receptors for hydrophobic signal molecules such as steroid and thyroid hormones and retinoic acid; the receptor-ligand complex acts as a transcription factor in the nucleus.
SH2 domain (Src homology region 2)
A protein domain present in many signalling proteins; binds a short amino acid sequence containing a phosphotyrosine.
Gap 2 phase of the eukaryotic cell cycle, between the end of DNA synthesis and the beginning of mitosis.
A carrier protein that transports 2 types of solute across the membrane in the same direction.
A large motor protein that undergoes ATP-dependent movement along microtubules.
A protein that binds tightly to a specific sugar.
Mutations that have occurred in the same cell as driver mutations, but which are irrelevant to the development of the cancer.
One of a family of cell-surface receptors that bind the tail region (Fc region) of an antibody molecule.
A family of ubiquitin ligases formed as a complex of several different proteins; one is involved in regulating the eukaryotic cell cycle, directing the destruction of inhibitors of S-Cdks in late G1 and thus promoting the activation of S-Cdks and DNA replication.
M6P receptor proteins
Transmembrane receptor proteins present in the trans Golgi network that recognize the mannose 6-phosphate (M6P) groups added exclusively to lysosomal enzymes, marking the enzymes for packaging and delivery to early endosomes.
A linear string of microtubule subunits joined end to end; multiple protofilaments associate with one another laterally to construct and provide strength and adaptability to microtubules.
A type of light microscope that exploits the interference effects that occur when light passes through material of different refractive indices; used to view living cells.
A storage form in cells for excess lipids; composed of a single monolayer of phospholipids and proteins that surrounds neutral lipids that can be retrieved from droplets as required by the cell.
A protein-sorting signal that consists of a specific 3D arrangement of atoms on the folded protein's surface.
The foreign or modified gene that has been added to create a transgenic organism.
Any glycolipid having 1 or more sialic acid (NANA) residues in its structure; found in the plasma membrane of eukaryotic cells and especially abundant in nerve cells.
A lipid molecule with a sugar residue or oligosaccharide attached.
A 4-pass transmembrane protein that is a component of gap junctions; 6 connexins assemble in the plasma membrane to form a connexon, or "hemichannel".
Division of the cytoplasm of a plant or animal cell into 2, as distinct from the associated division of its nucleus (which is mitosis); part of M phase.
A vesicle formed as material ingested by the cell during endocytosis is progressively enclosed by a small portion of the plasma membrane, which first invaginates and then pinches off to form the vesicle.
A communicating cell-cell junction that allows signals to pass from a nerve cell to another cell; the signal is carried by a diffusible neurotransmitter in a chemical synapse, or directly via gap junctions in an electrical synapse.
Inositol 1,4,5-trisphosphate (IP3)
A small intracellular signalling molecule produced during activation of the inositol phospholipid signalling pathway; acts to release Ca2+ from the ER.
Turbine-like protein machines constructed from multiple different subunits that use the energy of ATP hydrolysis to drive transport across a membrane; the V-type proton pump transfers H+ into organelles such as lysosomes to acidify their interior.
Histone chaperone (chromatin assembly factor)
A protein that binds free histones, releasing them once they have been incorporated into newly replicated chromatin.
A small, highly conserved protein present in all eukaryotic cells that becomes covalently attached to lysines of other proteins; attachment of a short chain of ubiquitins to such a lysine can tag a protein for intracellular proteolytic destruction by a proteasome.
Signal-recognition particle (SRP)
A ribonucleoprotein particle that binds an ER signal sequence on a partially synthesized polypeptide chain and directs the polypeptide and its attached ribosome to the ER.
An extracellular signal protein or peptide that acts as a local mediator in cell-cell communication.
A ribosome attached to the cytosolic face of the ER; the site of synthesis of proteins that enter the ER.
A structure made of microtubules and actin filaments that forms in the prospective plane of division of a plant cell and guides formation of the cell plate.
Specialized regions typically occupying about 2% of the total plasma membrane area at which the endocytic pathway often begins.
Channel-forming proteins of the outer membranes of bacteria, mitochondria, and chloroplasts.
The process whereby a cell progressively loses the potential to form other cell types, as development proceeds.
A mode of anaphase in which chromosome segregation occurs as spindle poles separate and move apart.
A member of the large cadherin superfamily of transmembrane adhesion proteins that mediates Ca2+-dependent cell-cell adhesion in animal tissues.
One of the 2 A subunits of anthrax toxin; an adenylyl cyclase that catalyzes production of cAMP, leading to ion imbalance and consequent edema in the skin or lung.
Phosphoinositide 3-kinase (PI 3-kinase)
A membrane-bound enzyme that is a component of the PI-3-kinase-Akt intracellular signalling pathway; it phosphorylates PI(4,5)P2 at the 3 position on the inositol ring to produce PI(3,4,5)P3 docking sites in the membrane for other intracellular signalling proteins.
A fibrous meshwork of proteins on the inner surface of the inner nuclear membrane, made up of a network of intermediate filaments formed from nuclear lamins.
The transition in the eukaryotic cell cycle preceding sister-chromatid separation at anaphase; if the cell is not ready to proceed to anaphase, the cell cycle is halted at this point.
A common receiving compartment with which most endocytic vesicles fuse and where internalized cargo is sorted either for return to the plasma membrane or for degradation by inclusion in a late endosome.
A motor protein associated with microtubules that transports cargo within the cell.
A cyclin found in all eukaryotic cells that promotes the events of mitosis.
A mutation that changes a protein or RNA molecule so that its function is altered only under some conditions, such as at an unusually high or low temperature.
The end of a chromosome, associated with a characteristic DNA sequence that is replicated in a special way; counteracts the tendency of the chromosome otherwise to shorten with each round of replication.
G-protein-coupled receptor (GPCR)
A 7-pass cell-surface receptor that, when activated by its extracellular ligand, activates a G protein, which in turn activates either an enzyme or ion channel in the plasma membrane.
A cyclin that activates Cdks in late G1 of the eukaryotic cell cycle and thereby helps trigger progression through Start, resulting in a commitment to cell-cycle entry; its level falls at the start of S phase.
Passive transport (facilitated diffusion)
Transport of a solute across a membrane down its concentration gradient or its electrochemical gradient, using only the energy stored in the gradient.
The reproductive cycle of a cell: the orderly sequence of events by which a cell duplicates its chromosomes and, usually, the other cell contents, and divides into two.
An intracellular signalling pathway that stimulates animal cells to survive and grow.
A state of withdrawal from the eukaryotic cell cycle by entry into a quiescent digression from the G1 phase; a common, sometimes permanent, state for differentiated cells.
A monomeric GTPase responsible for regulating COPII coat assembly at the ER membrane.
Alternative RNA splicing
The production of different RNAs from the same gene by splicing the transcript in different ways.
An RNA molecule with catalytic activity.
Any of a number of different proteins that make up nuclear pore complexes.
An enzyme that phosphorylates specific proteins on serines or threonines.
Tumour suppressor gene
A gene that appears to help prevent formation of a cancer; loss-of-function mutations in such genes favour the development of cancer.
A large protein complex in the cytosol with proteolytic activity that is responsible for degrading proteins that have been marked for destruction by ubiquitylation or by some other means.
Sudden conversion from growth to shrinkage, and vice versa, in a microtubule.
A clone containing double-stranded cDNA molecules derived from the protein-coding mRNA molecules present in a cell.
Human papillomavirus; infects the cervical epithelium and is important as a cause of carcinoma of the uterine cervix.
A member of 1 of the 2 main classes of motor proteins that use the energy of ATP hydrolysis to move along microtubules.
Transmembrane ion channels that open in response to a mechanical stress on the lipid bilayer in which they are embedded.
A member of a family of proteins that contributes to GPCR desensitization by preventing the activated receptor from interacting with G proteins and serving as an adaptor to couple the receptor to clathrin-dependent endocytosis.
Disparate chemicals that are carcinogenic, due to the ability to cause mutations, when fed to experimental animals or painted repeatedly on their skin.
A reaction in which a phosphate group is covalently coupled to another molecule.
Nuclear pore complex (NPC)
A large multiprotein structure forming an aqueous channel (the nuclear pore) through the nuclear envelope that allows selected molecules to move between nucleus and cytoplasm.
The excretion of material from the cell by vesicle fusion with the plasma membrane; can occur constitutively or be regulated.
Constitutive secretory pathway
A pathway present in all cells by which moelcules such as plasma membrane proteins are continually delivered to the plasma membrane from the Golgi in vesicles that fuse with the plasma membrane; the default route to the plasma membrane if no other sorting signals are present.
Src protein family
A family of cytoplasmic tyrosine kinases that associate with the cytoplasmic domains of some enzyme-linked cell surface receptors that lack intrinsic tyrosine kinase activity; they transmit a signal onward by phosphorylating the receptor itself and specific intracellular signalling proteins on tyrosines.
An engineered protein that combines 2 or more normally separate polypeptides; produced from a recombinant gene.
Scanning electron microscope
A type of electron microscope that produces an image of the surface of an object.
A transmembrane enzyme complex in the inner membrane of mitochondria and the thylakoid membrane of chloroplasts that catalyzes the formation of ATP from ADP and inorganic phosphate during oxidative phosphorylation and photosynthesis, respectively.
A compact protein module, found in many intracellular signalling proteins, that binds to a particular structural motif (e.g. a short peptide sequence, a covalent modification, or another protein domain) in another protein or lipid.
Ca2+/calmodulin-dependent kinase (CaM-kinase)
A serine/threonine protein kinase activated by Ca2+/calmodulin that indirectly mediates the effects of an increase in cytosolic Ca2+ by phosphorylating specific target proteins.
Members of a family of monomeric GTPases that have important roles in vesicle transport, being responsible for coat assembly at the membrane.
A protein translocator that helps β-barrel proteins to fold properly in the outer mitochondrial membrane.
Na+-K+ pump (Na+-K+ ATPase)
A 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.
An organelle that provides an intermediate stage on the passage of recycled receptors back to the cell membrane; regulates plasma membrane insertion of some proteins.
A heptamer of Apaf1 proteins that forms on activation of the intrinsic pathway; it recruits and activates initiator caspases that subsequently activate downstream executioner caspases to induce apoptosis.
A cell that carries out the final response or function in a particular process.
The digestion of cytoplasm and worn-out organelles by the cell's own lysosomes.
Low-density lipoprotein (LDL)
A 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.
The net drift of molecules through space due to random thermal movements.
A membrane-enclosed organelle in which molecules destined for secretion are stored prior to release.
Movement of proteins between the cytosol and the nucleus through nuclear pore complexes in the nuclear envelope that function as selective gates.
Multipass transmembrane protein
A membrane protein in which the polypeptide chain crosses the lipid bilayer more than once.
An altered gene whose product can act in a dominant fashion to help make a cell cancerous; typically, an oncogene is a mutant form of a normal gene (proto-oncogene) involved in the control of cell growth or division.
A member of the Rho family of monomeric GTPases that regulates the actin and microtubule cytoskeletons, cell-cycle progression, gene transcription, and membrane transport.
A complex organelle in eukaryotic cells, centred on a stack of flattened, membrane-enclosed spaces, in which proteins and lipids transferred from the ER are modified and sorted.
An insulating layer of specialized cell membrane wrapped around vertebrate axons.
A monomeric GTPase of the Ras superfamily present in both cytosol and nucleus; required for the active transport of macromolecules into and out of the nucleus through nuclear pore complexes.
A protein that periodically rises and falls in concentration in step with the eukaryotic cell cycle; cyclins activate crucial protein kinases (Cdk) and thereby help control progression from 1 stage of the cell cycle to the next.
A cluster of specialized cells in developing tissues that serves as a source of developmental signals (e.g. the generation of a morphogen gradient).
Replicative cell senescence
A phenomenon observed in primary cell cultures in which cell proliferationi slows down and finally irreversibly halts.
MAP (mitogen-activated protein) kinase module
An intracellular signalling module composed of 3 protein kinases, acting in sequence, with MAP kinase as the third; typically activated by a Ras protein in response to extracellular signals.
An activating subunit of the anaphase-promoting complex (APC/C).
Mutations that are causal factors in the development of cancer.
DNA sequences to which transcription regulators bind to control the rate of gene transcription; in nearly all cases, these sequences must be on the same chromosome (cis) to the genes they control.
A collection of cloned DNA molecules representing complementary DNA copies of the mRNA produced by a cell.
Nuclear export signal
A sorting signal contained in the structure of molecules and complexes that are transported from the nucleus to the cytosol through nuclear pore complexes.
A sheet of cells covering the outer surface of a structure or lining a cavity.
A monomeric Ras-related GTPase that in its active form (Rheb-GTP) activates mTOR, which promotes cell growth.
Regulated secretory pathway
A second secretory pathway found mainly in cells specialized for secreting products rapidly on demand (such as hormones, neurotransmitters, or digestive enzymes) in which soluble proteins and other substances are initially stored in secretory vesicles for later release.
A nucleotide sequence of DNA that has accumulated multiple mutations that have rendered an ancestral gene inactive and nonfunctional.
A deviation in the electric potential across the plasma membrane toward a positive value; a depolarized cell has a potential that is positive outside and negative inside.
An intracellular signalling pathway in which 1 protein kinase, activated by phosphorylation, phosphorylates the next protein kinase in the sequence, and so on, relaying the signal onward.
Coated vesicles that transport material from the plasma membrane and between endosomal and Golgi compartments.
A soluble component of the mitochondrial electron-transport chain; its release into the cytosol from the mitochondrial intermembrane space also initiates apoptosis.
A transmembrane protein complex that allows inorganic ions or other small molecules to diffuse passively across the lipid bilayer.
The gene that is defective in both copies in individuals with retinoblastoma; its protein product plays a central role in cell-cycle control.
A monomeric GTPase of the Ras superfamily that helps to relay signals from cell-surface tyrosine kinase receptors to the nucleus, frequently in response to signals that stimulate cell division.
Delayed K+ channel
A neuronal voltage-gated K+ channel that opens following membrane depolarization but during the falling phase of an action potential due to slower activation kinetics than Na+ channels; opening permits K+ efflux, driving the membrane potential back toward its original negative value, ready to transmit a second impulse.
1 of 2 or more genes that are similar in sequence as a result of derivation from the same ancestral gene; includes orthologs and paralogs.
An abundant lipid molecule with a characteristic 4-ring steroid structure; an important component in the plasma membranes of animal cells.
A compartment formed from a bulbous, vacuolar portion of early endosomes by a process called endosome maturation; late endosomes fuse with one another and with lysosomes to form endolysosomes that degrade their contents.
A defense mechanism in bacteria using small noncoding RNA molecules (crRNAs) to seek out and destroy invading viral genomes through complementary base-pairing and targeted nuclease digestion.
A membrane protein not extending into the hydrophobic interior of the lipid bilayer but bound to either face of the membrane by noncovalent interactions with other membrane proteins.
The process of moving a protein across a membrane.
The voltage difference across a membrane due to a slight excess of positive ions on one side and of negative ions on the other; a typical membrane potential for an animal cell plasma membrane is -60 mV (inside negative relative to the surrounding fluid).
A cytosolic GTPase that binds to the neck of a clathrin-coated vesicle in the process of budding from the membrane, and which is involved in completing vesicle formation.
Voltage-gated cation channel
A type of ion channel found in the membranes of electrically excitable cells (such as nerve, endocrine, egg, and muscle cells); opens in response to a shift in membrane potential past a threshold value.
Cortical fibres of contractile actin-myosin II bundles that connect the cell to the extracellular matrix or adjacent cells through focal adhesions or a circumferential belt and adherens junctions.
One of a large number of nucleases that can cleave a DNA molecule at any site where a specific short sequence of nucleotides occurs; extensively used in recombinant DNA technology.
A type of light microscope that produces a clear image of a given plane within a solid object, using a laser beam as a pinpoint source of illumination and scanning across the plane to produce a 2D optical section.
K+ leak channel
A K+-transporting ion channel in the plasma membrane of animal cells that remains open even in a "resting" cell.
Extracellular signal molecule
Any secreted or cell-surface chemical signal that binds to receptors and regulates the activity of the cell expressing the receptor.
An extracellular signal that promotes cell survival by inhibiting apoptosis.
Receptor tyrosine kinase (RTK)
A cell-surface receptor with an extracellular ligand-binding domain and an intracellular kinase domain that phosphorylates signalling proteins on tyrosine residues in response to ligand binding.
Intercellular signalling performed by neurons that transmit signals electrically along their axons and release neurotransmitters at synapses, which are often located far away from the neuronal cell body.
Short-range cell-cell communication via secreted signal molecules that act on neighbouring cells.
A collection of cloned DNA molecules, representing either an entire genome (genomic library) or complementary DNA copies of the mRNA produced by a cell (cDNA library).
A member of a class of cyclins that accumulate during late G1 phase and bind Cdks soon after progression through Start, and which help stimulate DNA replication and chromosome duplication; levels remain high until late mitosis, after which these cyclins are destroyed.
A 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.
Peripheral (secondary) lymphoid organ
A lymphoid organ in which T cells and B cells interact and respond to foreign antigens; examples are spleen, lymph nodes, and mucosal-associated lymphoid organs.
A transmembrane death receptor that initiates apoptosis when it binds its extracellular ligand (Fas ligand).
SRP (signal-recognition particle) receptor
A component in the ER membrane that guides the SRP to the ER membrane.
A hexameric ATPase that disassembles a trans-SNARE complex.
A carrier protein that transports a single solute from one side of the membrane to the other.
Nuclear import receptors
Receptor proteins that recognize nuclear localization signals to initiate nuclear import of proteins containing the appropriate nuclear localization signal.
A specialized layer of cytoplasm on the inner face of the plasma membrane; in animal cells, it is an actin-rich layer responsible for movements of the cell surface.
A microscope that uses a beam of electrons to create the image.
An enzyme that transfers the terminal phosphate group of ATP to 1 or more specific amino acids (serine, threonine, or tyrosine) of a target protein.
Genes or proteins from different species that are similar in sequence because they are descendants of the same gene in the last common ancestor of those species.
GTP-binding protein (GTPase)
An enzyme that converts GTP to GDP.
The main category of lipids used to construct biomembranes; generally composed of 2 fatty acids linked through glycerol (or sphingosine) phosphate to one of a variety of polar head groups.
ER retention signal
A short amino acid sequence on a protein that prevents it from moving out of the ER; found on ER resident proteins.
Coated vesicles that transport material early in the secretory pathway, budding from the ER.
mRNA engaged with multiple ribosomes in the act of translation.
An abnormally increased spontaneous mutation rate, such as occurs in cancer cells.
A normal light microscope in which the image is obtained by simple transmission of light through the object being viewed.
The cytoskeletal network in the cortical region of the cytosol just beneath the plasma membrane.
A signal molecule secreted by an endocrine cell into the bloodstream, which can then carry the signal to distant target cells.
The attachment of sister chromatids to opposite poles of the mitotic spindle, so that they move to opposite ends of the cell when they separate in anaphase.
An anchoring cell-cell junction, usually formed between 2 epithelial cells, characterized by dense plaques of protein into which intermediate filaments in the 2 adjoining cells insert.
An enzyme that joins the ends of 2 strands of DNA together with a covalent bond to make a continuous DNA strand.
The constricted region of a mitotic chromosome that holds sister chromatids together; this is also the site on the DNA where the kinetochore forms so as to capture microtubules from the mitotic spindle.
DNA tumour virus
A general term for a variety of different DNA viruses that can cause tumours.
A protein subunit of the intermediate filaments that form the nuclear lamina.
A protein that binds to the protease separase and thereby prevents its cleavage of the protein linkages that hold sister chromatids together in early mitosis; securin is destroyed at the metaphase-to-anaphase transition.
A long, whiplike protrusion whose undulations drive a cell through a fluid medium; eukaryotic flagella are longer versions of cilia.
Guanine nucleotide exchange factor (GEF)
A protein that binds to a GTPase and activates it by stimulating it to release its tightly bound GDP, thereby allowing it to bind GTP in its place.
A communicating channel-forming cell-cell junction present in most animal tissues that allows ions and small molecules to pass from the cytoplasm of 1 cell to the cytoplasm of the next.
A transmembrane SNARE protein, comprising a single polypeptide chain, usually found in vesicle membranes, where it interacts with t-SNAREs in target membranes.
A mode of anaphase in which chromosome segregation occurs as chromosomes move toward the two spindle poles.
A signal sequence or signal patch that directs the delivery of a protein to a specific location, such as a particular intracellular compartment.