BIOL 360 Glossary Terms Flashcards
1
Q
Cyclic AMP (cAMP)
A
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.
2
Q
ARP (actin-related protein) complex (Arp 2/3 complex)
A
A complex of proteins that nucleates actin filament growth from the minus end.
3
Q
Mitogen
A
An extracellular signal molecule that stimulates cells to proliferate.
4
Q
Pinocytosis
A
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.
5
Q
Transgenic organism
A
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.
6
Q
Primary tumour
A
A tumour at the original site at which a cancer first arose; secondary tumours develop elsewhere by metastasis.
7
Q
Protein tyrosine phosphatase
A
An enzyme that removes phosphate groups from phosphorylated tyrosine residues on proteins.
8
Q
Cilium
A
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.
9
Q
Tight junction
A
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.
10
Q
Homologous chromosomes
A
The maternal and paternal copies of a particular chromosome.
11
Q
Wnt protein
A
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.
12
Q
Differentiation
A
The process by which a cell undergoes a change to an overtly specialized cell type.
13
Q
Translational control
A
Regulation by a cell of gene expression by selecting which mRNAs in the cytoplasm are translated by ribosomes.
14
Q
ABC transporters
A
A large family of membrane transport proteins that use energy from ATP hydrolysis to transfer peptides or small molecules across membranes.
15
Q
mTOR
A
A large protein kinase involved in mammalian cell signalling.
16
Q
Single-pass transmembrane protein
A
A membrane protein in which the polypeptide chain crosses the lipid bilayer only once.
17
Q
Liposome
A
An artificial phospholipid bilayer vesicle formed from an aqueous suspension of phospholipid molecules.
18
Q
Serine protease
A
A type of protease that has a reactive serine in the active site.
19
Q
γ-tubulin ring complex (γ-TuRC)
A
A protein complex containing γ-tubulin and other proteins that is an efficient nucleator of microtubules and caps their minus ends.
20
Q
Wnt/β-catenin pathway
A
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.
21
Q
Phosphoinositide
A
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.
22
Q
Caspase
A
An intracellular protease that is involved in mediating the intracellular events of apoptosis.
23
Q
Mitochondrial precursor proteins
A
Proteins first fully synthesized in the cytosol and then translocated into mitochondrial subcompartments as directed by 1 or more signal sequences.
24
Q
Cohesin
A
A complex of proteins that holds sister chromatids together along their length before separation.
25
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.
26
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.
27
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.
28
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.
29
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.
30
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.
31
Endocytosis
The uptake of material into a cell by an invagination of the plasma membrane and its internalization in a membrane-enclosed vesicle.
32
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.
33
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.
34
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.
35
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.
36
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.
37
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.
38
PDZ domain
A protein-binding domain present in many scaffold proteins and often used as a docking site for intracellular tails of transmembrane proteins.
39
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.
40
Mutation
A heritable change in the nucleotide sequence of a chromosome.
41
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.
42
S phase
The period of a eukaryotic cell cycle in which DNA is synthesized.
43
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.
44
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.
45
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.
46
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.
47
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.
48
Mitotic chromosome
A highly condensed duplicated chromosome as seen at mitosis, consisting of 2 sister chromatids held together at the centromere.
49
Fluorescence resonance energy transfer (FRET)
A technique for monitoring the closeness of 2 fluorescently labelled molecules (and thus their interaction) in cells.
50
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).
51
Horizontal gene transfer
Gene transfer between bacteria via natural transformation or by released naked DNA, transduction by bacteriophages, or sexual exchange by conjugation.
52
Leukemia
Cancer of white blood cells.
53
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.
54
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.
55
Signal sequence
A short continuous sequence of amino acids that determines the eventual location of a protein in the cell.
56
Kinetochore
A large protein complex that connects the centromere of a chromosome to microtubules of the mitotic spindle.
57
Carcinoma
Cancer of epithelial cells; the most common form of human cancer.
58
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.
59
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.
60
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.
61
Microtubule-associated protein (MAP)
Any protein that binds to microtubules and modifies their properties, including structural and motor proteins.
62
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.
63
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.
64
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.
65
Death receptor
A transmembrane receptor protein that can signal the cell to undergo apoptosis when it binds its extracellular ligand (e.g. Ras).
66
Lymphoid organ
An organ containing large numbers of lymphocytes; lymphocytes are produced in primary lymphoid organs and respond to antigen in peripheral lymphoid organs.
67
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.
68
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.
69
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.
70
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.
71
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.
72
Plasmid vector
A small, circular molecule of double-stranded DNA derived from plasmids that occur naturally in bacterial cells; widely used for gene cloning.
73
Protein glycosylation
The process of transferring a single saccharide or preformed precursor oligosaccharide to proteins.
74
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).
75
*Ras* (genes)
A small family of proto-oncogenes that are frequently mutated in cancers, each of which produces a Ras monomeric GTPase.
76
Keratin
A type of intermediate filament commonly produced by epithelial cells.
77
Local mediator
An extracellular signal molecule that acts on neighbouring cells.
78
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.
79
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.
80
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.
81
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).
82
Inhibitory G protein (Gi)
A trimeric G protein that can regulate ion channels and inhibit the enzyme adenylyl cyclase in the plasma membrane.
83
Bacterial artificial chromosome (BAC)
A cloning vector that can accommodate large pieces of DNA, typically up to 1 million base pairs.
84
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.
85
Positive feedback
A control mechanism whereby the end product of a reaction or pathway stimulates its own production or activation.
86
Dendrite
An extension of a nerve cell, often elaborately branched, that receives stimuli from other nerve cells.
87
Chemotaxis
The movement of a cell toward or away from some diffusible chemical.
88
BiP
An ER-resident chaperone protein and member of the family of hsp70-type chaperone proteins.
89
Janus kinases (JAKs)
Cytoplasmic tyrosine kinases associated with cytokine receptors, which phosphorylate and activate transcription regulators called STATs.
90
Cell memory
The retention by cells and their descendants of persistently altered patterns of gene expression, without any change in DNA sequence (epigenetic inheritance).
91
Cyclic AMP phosphodiesterase
A specific enzyme that rapidly and continuously destroys cAMP, forming 5'-AMP.
92
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.
93
Astral microtubule
In the mitotic spindle, any of the microtubules radiating from the aster which are not attached to a kinetochore of a chromosome.
94
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.
95
Apaf1
An adaptor protein of the intrinsic apoptotic pathway; on binding cytochrome c, it oligomerizes to form an apoptosome.
96
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.
97
Fas ligand
A ligand that activates the cell-surface death receptor Fas, triggering the extrinsic pathway of apoptosis.
98
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.
99
p53
A transcription regulatory protein that is activated by damage to DNA and is involved in blocking further progression through the cell cycle.
100
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.
101
Sarcoma
Cancer of connective tissue.
102
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.
103
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.
104
ER tail-anchored proteins
Membrane proteins anchored in the ER membrane by a single transmembrane alpha helix contained at their C-terminus.
105
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).
106
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.
107
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.
108
Macropinocytosis
A clathrin-independent, dedicated degradative endocytic pathway induced in most cell types by cell-surface receptor activation by specific cargoes.
109
Phagosome
A large intracellular membrane-enclosed vesicle that is formed as a result of phagocytosis; contains ingested extracellular material.
110
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.
111
cAMP-dependent protein kinase (PKA)
An enzyme that phosphorylates target proteins in response to a rise in intracellular cAMP.
112
Microsome
A small vesicle derived from ER that is produced by fragmentation when cells are homogenized.
113
Lamellipodium
A flattened, sheetlike protrusion supported by a meshwork of actin filaments, which is extended at the leading edge of a crawling animal cell.
114
Telophase
The final stage of mitosis, in which the two sets of separated chromosomes decondense and become enclosed by nuclear envelopes.
115
DNA polymerase
An enzyme that synthesizes DNA by joining nucleotides together using a DNA template as a guide.
116
Interphase
The long period of the cell cycle between 1 mitosis and the next; includes G1, S, and G2.
117
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.
118
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).
119
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.
120
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.
121
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.
122
G1 phase
Gap 1 phase of the eukaryotic cell cycle, between the end of mitosis and the start of DNA synthesis.
123
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.
124
Rab effectors
Molecules that bind activated, membrane-bound Rab proteins and act as downstream mediators of vesicle transport, membrane tethering, and fusion.
125
Integrin
A transmembrane adhesion protein that is involved in the attachment of cells to the extracellular matrix and to each other.
126
Neuromuscular junction
A specialized chemical synapse between an axon terminal of a motor neuron and a skeletal muscle cell.
127
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.
128
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.
129
Rho family
A family of monomeric GTPases within the Ras superfamily involved in signalling the rearrangment of the cytoskeleton; includes Rho, Rac, and Cdc42.
130
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.
131
Base excision repair
A DNA repair pathway in which single faulty bases are removed from the DNA helix and replaced.
132
Ubiquitin ligase
Any one of a large number of enzymes that attach ubiquitin to a protein, often marking it for destruction in a proteasome.
133
Cdc20
An activating subunit of the anaphase-promoting complex (APC/C).
134
Lipid raft
A small region of a membrane enriched in sphingolipids and cholesterol.
135
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.
136
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.
137
Cdc25
A protein phosphatase that dephosphorylates Cdks and increases their activity.
138
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.
139
Selectivity filter
The part of an ion channel structure that determines which ions it can transport.
140
Telomerase
An enzyme that elongates telomere sequences in DNA, which occur at the ends of eukaryotic chromosomes.
141
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.
142
Malignant
Of tumours and tumour cells: invasive and/or able to undergo metastasis; a malignant tumour is a cancer.
143
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.
144
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.
145
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.
146
Filopodium
A thin, spike-like protrusion with an actin filament core, generated on the leading edge of a crawling animal cell.
147
Myosin
A type of motor protein that uses the energy of ATP hydrolysis to move along actin filaments.
148
Morphogenesis
A developmental process in which cells undergo movements and deformations in order to assemble into tissues and organs with specific shapes and sizes.
149
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.
150
Tubulin
The protein subunit of microtubules.
151
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.
152
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.
153
Cell-cycle control system
A network of regulatory proteins that governs progression of a eukaryotic cell through the cell cycle.
154
Metastasis
The spread of cancer cells from their site of origin to other sites in the body.
155
Antiporter
A carrier protein that transports 2 different ions or small molecules across a membrane in opposite directions, either simultaneously or in sequence.
156
Post-translational
Occurring after completion of translation.
157
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.
158
COPI-coated vesicles
Coated vesicles that transport material early in the secretory pathway, budding from Golgi compartments.
159
Neuron (nerve cell)
An impulse-conducting cell of the nervous system, with extensive processes specialized to receive, conduct, and transmit signals.
160
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.
161
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.
162
Cytokine receptor
A cell-surface receptor that binds a specific cytokine or hormone and acts through the JAK-STAT signalling pathway.
163
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.
164
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.
165
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.
166
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.
167
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.
168
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.
169
ARF proteins
Monomeric GTPases in the Ras superfamily responsible for regulating both COPI coat assembly and clathrin coat assembly.
170
Committed precursor
A cell derived from a stem cell that divides for a limited number of times before terminally differentiating.
171
Executioner caspases
Apoptotic caspases that catalyze the widespread cleavage events during apoptosis that kill the cell.
172
TOM complex
A multisubunit protein complex that transports proteins across the mitochondrial outer membrane.
173
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.
174
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.
175
Cdk inhibitor protein (CKI)
A protein that binds to and inhibits cyclin-Cdk complexes, primarily involved in the control of G1 and S phases.
176
Focal adhesion kinase (FAK)
A cytoplasmic tyrosine kinase present at cell-matrix junctions (focal adhesions) in association with the cytoplasmic tails of integrins.
177
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.
178
Tumour virus
A virus that can help make the cell it infects cancerous.
179
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.
180
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.
181
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.
182
Multivesicular bodies
Intermediates in the endosome maturation process; early endosomes that are on their way to becoming late endosomes.
183
Somatic cell
Any cell of a plant or animal other than cells of the germ line.
184
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).
185
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.
186
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.
187
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.
188
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.
189
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.
190
Replication origin
The location on a DNA molecule at which duplication of the DNA begins.
191
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.
192
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.
193
Proteoglycan
A molecule consisting of 1 or more glycosaminoglycan chains attached to a core protein.
194
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.
195
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.
196
Glycoprotein
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.
197
Diacylglycerol (DAG)
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.
198
Photoactivation
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.
199
Neurotransmitter
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.
200
Promoter
A nucleotide sequence in DNA to which RNA polymerase binds to begin transcription.
201
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.
202
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.
203
Papillomaviruses
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.
204
Somatic mutations
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.
205
Axon
A long nerve cell projection that can rapidly conduct nerve impulses over long distances to deliver signals to other cells.
206
Enzyme-coupled receptor
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.
207
Superresolution
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.
208
CG island
A region of DNA in vertebrate genomes with a greater than average density of CG sequences; these regions generally remain unmethylated.
209
Receptor-mediated endocytosis
Internalization of receptor-ligand complexes from the plasma membrane by endocytosis.
210
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.
211
Apoptosis
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.
212
Sec61 complex
The 3-subunit core of the protein translocator that transfers polypeptide chains across the ER membrane.
213
Stimulatory G protein (Gs)
A G protein that, when activated, activates the enzyme adenylyl cyclase and thus stimulates the production of cAMP.
214
Adaptor protein
A protein that functions solely to link 2 or more different proteins together in an intracellular signalling pathway or protein complex.
215
Initiator caspases
Apoptotic caspases that begin the apoptotic process, activating the executioner caspases.
216
Nuclear transport receptor
A protein that escorts macromolecules into or out of the nucleus.
217
Rab proteins
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.
218
Start-transfer signal
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.
219
Bax
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.
220
Growth factor
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.
221
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).
222
Ligand
Any molecule that binds to a specific site on a protein or other molecule.
223
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).
224
Microtubule-organizing centre (MTOC)
A region in a cell, such as a centrosome or a basal body, from which microtubules grow.
225
Calreticulin
A carbohydrate-binding chaperone protein in the ER lumen that binds to oligosaccharides on incompletely folded proteins and retains them in the ER.
226
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.
227
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.
228
Complex oligosaccharides
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.
229
Coiled-coil
An especially stable rodlike protein structure formed by 2 or more alpha helices coiled around each other.
230
Inhibitors of apoptosis (IAPs)
Intracellular protein inhibitors of apoptosis.
231
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.
232
Syncytium
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.
233
Transcriptional control
Regulation by a cell of gene expression by controlling when and how often a given gene is transcribed.
234
Centriole
A short cylindrical array of microtubules; a pair of centrioles is usually found at the centre of a centrosome in animal cells.
235
DNA supercoiling
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.
236
Extrinsic pathway
The pathway of apoptosis triggered by extracellular signal proteins binding to cell-surface death receptors.
237
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.
238
Separase
A protease that cleaves the cohesin protein linkages that hold sister chromatids together; acts at anaphase, enabling chromatid separation and segregation.
239
Lysosome
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.
240
*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.
241
Bcl2 family
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.
242
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.
243
Colorectal cancer
Cancer arising from the epithelium lining the colon (large intestine) and rectum (terminal segment of the gut).
244
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.
245
Treadmilling
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.
246
Clathrin
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.
247
Stem cell
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).
248
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.
249
Molecular chaperone
A protein that helps guide the proper folding of other proteins, or helps them avoid misfolding; includes heat-shock proteins (hsp).
250
DNA helicase
An enzyme that is involved in opening the DNA helix into its single strands for DNA replication.
251
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.
252
Cdk-activating kinase (CAK)
A protein kinase that phosphorylates Cdks in cyclin-Cdk complexes, activating the Cdk.
253
Multidrug resistance
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.
254
Cytoskeleton
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.
255
Transcription regulators
Any protein that binds to a specific DNA sequence to influence the transcription of a gene.
256
Gq
A class of G protein that couples GPCRs to phospholipase C-β (PLC-β) to activate the inositol phospholipid signalling pathway.
257
Centrosome
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.
258
Stop-transfer signal
A hydrophobic amino acid sequence that halts translocation of a polypeptide chain through the ER membrane, thus anchoring the protein in the membrane.
259
Mutation rate
The rate at which changes (mutations) occur in DNA sequences.
260
Contact-dependent signalling
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.
261
Neurofilament
A type of intermediate filament found in nerve cells.
262
Green fluorescent protein (GFP)
A fluorescent protein, isolated from a jellyfish, widely used as a marker in cell biology.
263
GPCR kinase (GRK)
A member of a family of enzymes that phosphorylates multiple serines and threonines on a GPCR to produce receptor desensitization.
264
OXA complex
A protein translocator in the inner mitochondrial membrane that mediates insertion of inner membrane proteins.
265
Growth hormone (GH)
A mammalian hormone secreted by the pituitary gland into the bloodstream that stimulates growth throughout the body.
266
Calnexin
A carbohydrate-binding chaperone protein in the ER membrane that binds to oligosaccharides on incompletely folded proteins and retains them in the ER.
267
*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.
268
High-mannose oligosaccharides
A broad class of *N*-linked oligosaccharides, attached to mammalian glycoproteins in the ER, containing 2 *N*-acetylglucosamine residues and many mannose residues.
269
Terminal differentiation
The limit of cell determination, when a cell forms one of the highly specialized cell types of the adult body.
270
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.
271
Restriction point
The important transition at the end of G1 in the eukaryotic cell cycle; commits the cell to enter S phase.
272
Condensin
A complex of proteins involved in chromosome condensation prior to mitosis; a target for M-Cdk.
273
Calmodulin
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.
274
Glycogen
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.
275
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.
276
Tyrosine-kinase-associated receptor
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.
277
Membrane protein
An amphiphilic protein of diverse structure and function that associates with the lipid bilayer of cell membranes.
278
Proto-oncogene
A normal gene, usually concerned with the regulation of cell proliferation, that can be converted into a cancer-promoting oncogene by mutation.
279
DNA primase
An enzyme that synthesizes a short strand of RNA on a DNA template, producing a primer for DNA synthesis.
280
Anti-IAP
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.
281
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.
282
t-SNARE
A transmembrane SNARE protein, usually composed of 3 proteins and found on target membranes, where it interacts with v-SNAREs on vesicle membranes.
283
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.
284
Steroid hormones
Hormones, including cortisol, estrogen, and testosterone, that are hydrophobic lipid molecules derived from cholesterol that activate intracellular nuclear receptors.
285
Endocrine cell
A specialized animal cell that secretes a hormone into the blood; usually part of a gland, such as the thyroid or pituitary gland.
286
Interpolar microtubule
In the mitotic spindle, a microtubule interdigitating at the equator with the microtubules emanating from the other pole.
287
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.
288
Phase variation
The random switching of phenotype and expression of proteins involved in infection at frequencies much higher than mutation rates.
289
DNA-only transposon
A transposable element that exists as DNA throughout its life cycle; many move by cut-and-paste transposition.
290
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.
291
Contractile ring
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.
292
Column chromatography
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.
293
Patch-clamp recording
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.
294
Noncoding RNA
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.
295
Adenylyl cyclase
A membrane-bound enzyme that catalyzes the formation of cAMP from ATP; an important component of some intracellular signalling pathways
296
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.
297
Feedback inhibition
The process in which a product of a reaction feeds back to inhibit a previous reaction in the same pathway.
298
Lymphoma
Cancer of lymphocytes, in which the cancer cells are mainly found in lymphoid organs (rather than in the blood, as in leukemias).
299
Signal peptidase
An enzyme that removes a terminal signal sequence from a protein once the sorting process is complete.
300
Heterochromatin
Chromatin that is highly condensed even in interphase; generally transcriptionally inactive.
301
Chromosome
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.
302
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.
303
Anaphase
The stage of mitosis during which sister chromatids separate and move away from each other.
304
*p53* (gene)
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.
305
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.
306
Phosphoglyceride
A phospholipid derived from glycerol, abundant in biomembranes.
307
Olfactory receptors
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.
308
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.
309
Motor protein
A protein that uses energy derived from ATP or GTP hydrolysis to propel itself along a linear track (protein filament or other polymeric molecule).
310
GPI anchor
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.
311
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).
312
Bak
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.
313
Tumour progression
The process by which an initial mildly disordered cell behaviour gradually evolves into a full-blown cancer.
314
WASp protein
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.
315
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.
316
Kinetochore
In the mitotic spindle, a microtubule that connects the spindle pole to the kinetochore of a chromosome.
317
Cell doctrine
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.
318
Protein phosphatase
An enzyme that catalyzes phosphate removal from amino acids of a target protein.
319
Hybridoma
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.
320
Germ cell
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.
321
G1-Cdk
A cyclin-Cdk complex formed in vertebrate cells by a G1-cyclin and the corresponding Cdk.
322
Rho
A member of the Rho family of monomeric GTPases that regulate the actin and microtubule cytoskeletons, cell-cycle progression, gene transcription, and membrane transport.
323
Cargo
The membrane components and soluble molecules carried by transport vesicles.
324
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.
325
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.
326
SH2 domain (Src homology region 2)
A protein domain present in many signalling proteins; binds a short amino acid sequence containing a phosphotyrosine.
327
G2 phase
Gap 2 phase of the eukaryotic cell cycle, between the end of DNA synthesis and the beginning of mitosis.
328
Symporter
A carrier protein that transports 2 types of solute across the membrane in the same direction.
329
Dynein
A large motor protein that undergoes ATP-dependent movement along microtubules.
330
Lectin
A protein that binds tightly to a specific sugar.
331
Passengers
Mutations that have occurred in the same cell as driver mutations, but which are irrelevant to the development of the cancer.
332
Fc receptor
One of a family of cell-surface receptors that bind the tail region (Fc region) of an antibody molecule.
333
SCF
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.
334
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.
335
Protofilament
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.
336
Phase-contrast microscope
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.
337
Lipid droplets
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.
338
Signal patch
A protein-sorting signal that consists of a specific 3D arrangement of atoms on the folded protein's surface.
339
Transgene
The foreign or modified gene that has been added to create a transgenic organism.
340
Ganglioside
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.
341
Glycolipid
A lipid molecule with a sugar residue or oligosaccharide attached.
342
Connexin
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".
343
Cytokinesis
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.
344
Endocytic vesicle
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.
345
Synapse
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.
346
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.
347
V-type pumps
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.
348
Histone chaperone (chromatin assembly factor)
A protein that binds free histones, releasing them once they have been incorporated into newly replicated chromatin.
349
Ubiquitin
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.
350
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.
351
Cytokine
An extracellular signal protein or peptide that acts as a local mediator in cell-cell communication.
352
Membrane-bound ribosome
A ribosome attached to the cytosolic face of the ER; the site of synthesis of proteins that enter the ER.
353
Phragmoplast
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.
354
Clathrin-coated pits
Specialized regions typically occupying about 2% of the total plasma membrane area at which the endocytic pathway often begins.
355
Porins
Channel-forming proteins of the outer membranes of bacteria, mitochondria, and chloroplasts.
356
Cell determination
The process whereby a cell progressively loses the potential to form other cell types, as development proceeds.
357
Anaphase B
A mode of anaphase in which chromosome segregation occurs as spindle poles separate and move apart.
358
Cadherin
A member of the large cadherin superfamily of transmembrane adhesion proteins that mediates Ca2+-dependent cell-cell adhesion in animal tissues.
359
Edema factor
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.
360
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.
361
Nuclear lamina
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.
362
Metaphase-to-anaphase transition
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.
363
Early endosome
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.
364
Kinesin-1
A motor protein associated with microtubules that transports cargo within the cell.
365
M-cyclin
A cyclin found in all eukaryotic cells that promotes the events of mitosis.
366
Conditional mutation
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.
367
Telomere
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.
368
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.
369
G1/S-cyclin
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.
370
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.
371
Cell cycle
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.
372
PI-3-kinase-Akt pathway
An intracellular signalling pathway that stimulates animal cells to survive and grow.
373
G0 phase
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.
374
Sar1 protein
A monomeric GTPase responsible for regulating COPII coat assembly at the ER membrane.
375
Alternative RNA splicing
The production of different RNAs from the same gene by splicing the transcript in different ways.
376
Ribozyme
An RNA molecule with catalytic activity.
377
Nucleoporin
Any of a number of different proteins that make up nuclear pore complexes.
378
Serine/threonine kinase
An enzyme that phosphorylates specific proteins on serines or threonines.
379
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.
380
Proteasome
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.
381
Dynamic instability
Sudden conversion from growth to shrinkage, and vice versa, in a microtubule.
382
cDNA clone
A clone containing double-stranded cDNA molecules derived from the protein-coding mRNA molecules present in a cell.
383
HPV
Human papillomavirus; infects the cervical epithelium and is important as a cause of carcinoma of the uterine cervix.
384
Kinesin
A member of 1 of the 2 main classes of motor proteins that use the energy of ATP hydrolysis to move along microtubules.
385
Mechanosensitive channels
Transmembrane ion channels that open in response to a mechanical stress on the lipid bilayer in which they are embedded.
386
Arrestin
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.
387
Chemical carcinogens
Disparate chemicals that are carcinogenic, due to the ability to cause mutations, when fed to experimental animals or painted repeatedly on their skin.
388
Phosphorylation
A reaction in which a phosphate group is covalently coupled to another molecule.
389
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.
390
Exocytosis
The excretion of material from the cell by vesicle fusion with the plasma membrane; can occur constitutively or be regulated.
391
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.
392
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.
393
Fusion protein
An engineered protein that combines 2 or more normally separate polypeptides; produced from a recombinant gene.
394
Scanning electron microscope
A type of electron microscope that produces an image of the surface of an object.
395
ATP synthase
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.
396
Interaction domain
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.
397
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.
398
Coat-recruitment GTPases
Members of a family of monomeric GTPases that have important roles in vesicle transport, being responsible for coat assembly at the membrane.
399
SAM complex
A protein translocator that helps β-barrel proteins to fold properly in the outer mitochondrial membrane.
400
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.
401
Recycling endosome
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.
402
Apoptosome
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.
403
Effector cell
A cell that carries out the final response or function in a particular process.
404
Autophagy
The digestion of cytoplasm and worn-out organelles by the cell's own lysosomes.
405
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.
406
Diffusion
The net drift of molecules through space due to random thermal movements.
407
Secretory vesicle
A membrane-enclosed organelle in which molecules destined for secretion are stored prior to release.
408
Gated transport
Movement of proteins between the cytosol and the nucleus through nuclear pore complexes in the nuclear envelope that function as selective gates.
409
Multipass transmembrane protein
A membrane protein in which the polypeptide chain crosses the lipid bilayer more than once.
410
Oncogene
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.
411
Cdc42
A member of the Rho family of monomeric GTPases that regulates the actin and microtubule cytoskeletons, cell-cycle progression, gene transcription, and membrane transport.
412
Golgi apparatus
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.
413
Myelin sheath
An insulating layer of specialized cell membrane wrapped around vertebrate axons.
414
Ran
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.
415
Cyclin
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.
416
Signalling centre
A cluster of specialized cells in developing tissues that serves as a source of developmental signals (e.g. the generation of a morphogen gradient).
417
Replicative cell senescence
A phenomenon observed in primary cell cultures in which cell proliferationi slows down and finally irreversibly halts.
418
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.
419
Cdh1
An activating subunit of the anaphase-promoting complex (APC/C).
420
Drivers
Mutations that are causal factors in the development of cancer.
421
*Cis*-regulatory sequences
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.
422
cDNA library
A collection of cloned DNA molecules representing complementary DNA copies of the mRNA produced by a cell.
423
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.
424
Epithelium
A sheet of cells covering the outer surface of a structure or lining a cavity.
425
Rheb
A monomeric Ras-related GTPase that in its active form (Rheb-GTP) activates mTOR, which promotes cell growth.
426
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.
427
Pseudogene
A nucleotide sequence of DNA that has accumulated multiple mutations that have rendered an ancestral gene inactive and nonfunctional.
428
Depolarization
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.
429
Kinase cascade
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.
430
Clathrin-coated vesicles
Coated vesicles that transport material from the plasma membrane and between endosomal and Golgi compartments.
431
Cytochrome c
A soluble component of the mitochondrial electron-transport chain; its release into the cytosol from the mitochondrial intermembrane space also initiates apoptosis.
432
Channel
A transmembrane protein complex that allows inorganic ions or other small molecules to diffuse passively across the lipid bilayer.
433
*Rb* gene
The gene that is defective in both copies in individuals with retinoblastoma; its protein product plays a central role in cell-cycle control.
434
Ras
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.
435
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.
436
Homolog
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.
437
Cholesterol
An abundant lipid molecule with a characteristic 4-ring steroid structure; an important component in the plasma membranes of animal cells.
438
Late endosome
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.
439
CRISPR
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.
440
Membrane-associated protein
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.
441
Protein translocation
The process of moving a protein across a membrane.
442
Membrane potential
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).
443
Dynamin
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.
444
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.
445
Stress fibres
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.
446
Restriction nuclease
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.
447
Confocal microscope
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.
448
K+ leak channel
A K+-transporting ion channel in the plasma membrane of animal cells that remains open even in a "resting" cell.
449
Extracellular signal molecule
Any secreted or cell-surface chemical signal that binds to receptors and regulates the activity of the cell expressing the receptor.
450
Survival factor
An extracellular signal that promotes cell survival by inhibiting apoptosis.
451
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.
452
Synaptic signalling
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.
453
Paracrine signalling
Short-range cell-cell communication via secreted signal molecules that act on neighbouring cells.
454
DNA library
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).
455
S-cyclin
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.
456
Inhibitory neurotransmitter
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.
457
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.
458
Fas
A transmembrane death receptor that initiates apoptosis when it binds its extracellular ligand (Fas ligand).
459
SRP (signal-recognition particle) receptor
A component in the ER membrane that guides the SRP to the ER membrane.
460
NSF
A hexameric ATPase that disassembles a trans-SNARE complex.
461
Uniporter
A carrier protein that transports a single solute from one side of the membrane to the other.
462
Nuclear import receptors
Receptor proteins that recognize nuclear localization signals to initiate nuclear import of proteins containing the appropriate nuclear localization signal.
463
Cell cortex
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.
464
Electron microscope
A microscope that uses a beam of electrons to create the image.
465
Protein kinase
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.
466
Orthologs
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.
467
GTP-binding protein (GTPase)
An enzyme that converts GTP to GDP.
468
Phospholipid
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.
469
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.
470
COPII-coated vesicles
Coated vesicles that transport material early in the secretory pathway, budding from the ER.
471
Polyribosome
mRNA engaged with multiple ribosomes in the act of translation.
472
Genetic instability
An abnormally increased spontaneous mutation rate, such as occurs in cancer cells.
473
Bright-field microscope
A normal light microscope in which the image is obtained by simple transmission of light through the object being viewed.
474
Cortex
The cytoskeletal network in the cortical region of the cytosol just beneath the plasma membrane.
475
Hormone
A signal molecule secreted by an endocrine cell into the bloodstream, which can then carry the signal to distant target cells.
476
Bi-orientation
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.
477
Desmosome
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.
478
DNA ligase
An enzyme that joins the ends of 2 strands of DNA together with a covalent bond to make a continuous DNA strand.
479
Centromere
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.
480
DNA tumour virus
A general term for a variety of different DNA viruses that can cause tumours.
481
Nuclear lamin
A protein subunit of the intermediate filaments that form the nuclear lamina.
482
Securin
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.
483
Flagellum
A long, whiplike protrusion whose undulations drive a cell through a fluid medium; eukaryotic flagella are longer versions of cilia.
484
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.
485
Gap junction
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.
486
v-SNARE
A transmembrane SNARE protein, comprising a single polypeptide chain, usually found in vesicle membranes, where it interacts with t-SNAREs in target membranes.
487
Anaphase A
A mode of anaphase in which chromosome segregation occurs as chromosomes move toward the two spindle poles.
488
Sorting signal
A signal sequence or signal patch that directs the delivery of a protein to a specific location, such as a particular intracellular compartment.
