BIOL 360 Glossary Terms Flashcards
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.
Mitogen
An extracellular signal molecule that stimulates cells to proliferate.
Pinocytosis
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.
Transgenic organism
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.
Primary tumour
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.
Cilium
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.
Tight junction
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.
Homologous chromosomes
The maternal and paternal copies of a particular chromosome.
Wnt protein
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.
Differentiation
The process by which a cell undergoes a change to an overtly specialized cell type.
Translational control
Regulation by a cell of gene expression by selecting which mRNAs in the cytoplasm are translated by ribosomes.
ABC transporters
A large family of membrane transport proteins that use energy from ATP hydrolysis to transfer peptides or small molecules across membranes.
mTOR
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.
Liposome
An artificial phospholipid bilayer vesicle formed from an aqueous suspension of phospholipid molecules.
Serine protease
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.
Wnt/β-catenin pathway
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.
Phosphoinositide
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.
Caspase
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.
Cohesin
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.
Endosome maturation
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.
Wee1
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.
Electrochemical gradient
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.
Endocytosis
The uptake of material into a cell by an invagination of the plasma membrane and its internalization in a membrane-enclosed vesicle.
DNA microarray
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.
Paralogs
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.
Exon
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.
Mitotic spindle
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.
PDZ domain
A protein-binding domain present in many scaffold proteins and often used as a docking site for intracellular tails of transmembrane proteins.
Aquaporin
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.
Mutation
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.
S phase
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.
Notch
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.
Mitochondrial hsp70
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.
Metastases
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.
Mitotic chromosome
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.
Coated vesicle
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.
Leukemia
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.
Signal sequence
A short continuous sequence of amino acids that determines the eventual location of a protein in the cell.
Kinetochore
A large protein complex that connects the centromere of a chromosome to microtubules of the mitotic spindle.
Carcinoma
Cancer of epithelial cells; the most common form of human cancer.
Oxidative phosphorylation
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.
Membrane-bending proteins
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.
Myc
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.
BH3-only 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.
CaM-kinase II
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.
Scaffold protein
A protein that binds groups of intracellular signalling proteins into a signalling complex, often anchoring the complex at a specific location in the cell.
Death receptor
A transmembrane receptor protein that can signal the cell to undergo apoptosis when it binds its extracellular ligand (e.g. Ras).
Lymphoid organ
An organ containing large numbers of lymphocytes; lymphocytes are produced in primary lymphoid organs and respond to antigen in peripheral lymphoid organs.
Akt
A serine/threonine protein kinase that acts in the PI 3-kinase/Akt intracellular signalling pathway involved in signalling cells to grow and survive.
Bcl2
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.
Rab cascade
An ordered recruitment of sequentially acting Rab proteins into Rab domains on membranes, which changes the identity of an organelle and reassigns membrane dynamics.
Plasmid vector
A small, circular molecule of double-stranded DNA derived from plasmids that occur naturally in bacterial cells; widely used for gene cloning.
Protein glycosylation
The process of transferring a single saccharide or preformed precursor oligosaccharide to proteins.
Cdc6
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).
Ras (genes)
A small family of proto-oncogenes that are frequently mutated in cancers, each of which produces a Ras monomeric GTPase.
Keratin
A type of intermediate filament commonly produced by epithelial cells.
Local mediator
An extracellular signal molecule that acts on neighbouring cells.
Synapse elimination
The process by which each muscle cell at first receives synapses from several motor neurons, but is ultimately left innervated by only one.
Single-particle reconstruction
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.
DNA topoisomerase
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.
Transformed cell
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.
Transporter
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.
Positive feedback
A control mechanism whereby the end product of a reaction or pathway stimulates its own production or activation.
Dendrite
An extension of a nerve cell, often elaborately branched, that receives stimuli from other nerve cells.
Chemotaxis
The movement of a cell toward or away from some diffusible chemical.
BiP
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.
Cell memory
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.
Hedgehog protein
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.
Astral microtubule
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.
Apaf1
An adaptor protein of the intrinsic apoptotic pathway; on binding cytochrome c, it oligomerizes to form an apoptosome.
Sister chromatids
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.
Fas ligand
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.
p53
A transcription regulatory protein that is activated by damage to DNA and is involved in blocking further progression through the cell cycle.
Histone
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.
Sarcoma
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.
Alpha helix
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.
Cdt1
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).
Chromatin
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.
Macropinocytosis
A clathrin-independent, dedicated degradative endocytic pathway induced in most cell types by cell-surface receptor activation by specific cargoes.
Phagosome
A large intracellular membrane-enclosed vesicle that is formed as a result of phagocytosis; contains ingested extracellular material.
Dark-field microscopy
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.
Microsome
A small vesicle derived from ER that is produced by fragmentation when cells are homogenized.
Lamellipodium
A flattened, sheetlike protrusion supported by a meshwork of actin filaments, which is extended at the leading edge of a crawling animal cell.
Telophase
The final stage of mitosis, in which the two sets of separated chromosomes decondense and become enclosed by nuclear envelopes.
DNA polymerase
An enzyme that synthesizes DNA by joining nucleotides together using a DNA template as a guide.
Interphase
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.
Lymphocyte
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).
Ion-channel-coupled receptor
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.
Axoneme
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.
G1 phase
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.
Rab effectors
Molecules that bind activated, membrane-bound Rab proteins and act as downstream mediators of vesicle transport, membrane tethering, and fusion.
Integrin
A transmembrane adhesion protein that is involved in the attachment of cells to the extracellular matrix and to each other.
Neuromuscular junction
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.
Microtubule flux
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.
Rho family
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.
Ubiquitin ligase
Any one of a large number of enzymes that attach ubiquitin to a protein, often marking it for destruction in a proteasome.
Cdc20
An activating subunit of the anaphase-promoting complex (APC/C).
Lipid raft
A small region of a membrane enriched in sphingolipids and cholesterol.
Basal lamina
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.
Ion channel
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.
Cdc25
A protein phosphatase that dephosphorylates Cdks and increases their activity.
Differential-interference-phase-contrast microscope
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.
Selectivity filter
The part of an ion channel structure that determines which ions it can transport.
Telomerase
An enzyme that elongates telomere sequences in DNA, which occur at the ends of eukaryotic chromosomes.
Formin
A dimeric protein that nucleates the growth of straight, unbranched actin filaments that can be cross-linked by other proteins to form parallel bundles.
Malignant
Of tumours and tumour cells: invasive and/or able to undergo metastasis; a malignant tumour is a cancer.
P-type pumps
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.
Action potential
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.
Filopodium
A thin, spike-like protrusion with an actin filament core, generated on the leading edge of a crawling animal cell.
Myosin
A type of motor protein that uses the energy of ATP hydrolysis to move along actin filaments.
Morphogenesis
A developmental process in which cells undergo movements and deformations in order to assemble into tissues and organs with specific shapes and sizes.
Delta
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.
Tubulin
The protein subunit of microtubules.
G1-cyclin
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.
Monoclonal antibody
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.
Metastasis
The spread of cancer cells from their site of origin to other sites in the body.
Antiporter
A carrier protein that transports 2 different ions or small molecules across a membrane in opposite directions, either simultaneously or in sequence.
Post-translational
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.
COPI-coated vesicles
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.
Monomeric GTPases
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.
Cytokine receptor
A cell-surface receptor that binds a specific cytokine or hormone and acts through the JAK-STAT signalling pathway.
Morphogen
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.
Rac
A member of the Rho family of monomeric GTPases that regulate the actin and microtubule cytoskeletons, cell-cycle progression, gene transcription, and membrane transport.
Excitatory neurotransmitter
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.
DNA methylation
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.
Fluorescence microscope
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.
ARF proteins
Monomeric GTPases in the Ras superfamily responsible for regulating both COPI coat assembly and clathrin coat assembly.
Committed precursor
A cell derived from a stem cell that divides for a limited number of times before terminally differentiating.
Executioner caspases
Apoptotic caspases that catalyze the widespread cleavage events during apoptosis that kill the cell.
TOM complex
A multisubunit protein complex that transports proteins across the mitochondrial outer membrane.
Transport vesicles
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.
Codon
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.
Tumour virus
A virus that can help make the cell it infects cancerous.
Beta sheet
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.
Geminin
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.
TIM complexes
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.
Multivesicular bodies
Intermediates in the endosome maturation process; early endosomes that are on their way to becoming late endosomes.
Somatic cell
Any cell of a plant or animal other than cells of the germ line.
Adherens junction
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).
Second messenger
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.
E2F protein
A transcription regulatory protein that switches on many genes that encode proteins required for entry into the S phase of the cell cycle.
Retinoblastoma
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.
Hybridization
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.
G2/M transition
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.
Replication origin
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.
PI(4,5)P2
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.
Proteoglycan
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.
Connexon
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.
