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Flashcards in BIOL 360 Glossary Terms Deck (488):
1

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.

2

ARP (actin-related protein) complex (Arp 2/3 complex)

A complex of proteins that nucleates actin filament growth from the minus end.

3

Mitogen

An extracellular signal molecule that stimulates cells to proliferate.

4

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.

5

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.

6

Primary tumour

A tumour at the original site at which a cancer first arose; secondary tumours develop elsewhere by metastasis.

7

Protein tyrosine phosphatase

An enzyme that removes phosphate groups from phosphorylated tyrosine residues on proteins.

8

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.

9

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.

10

Homologous chromosomes

The maternal and paternal copies of a particular chromosome.

11

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.

12

Differentiation

The process by which a cell undergoes a change to an overtly specialized cell type.

13

Translational control

Regulation by a cell of gene expression by selecting which mRNAs in the cytoplasm are translated by ribosomes.

14

ABC transporters

A large family of membrane transport proteins that use energy from ATP hydrolysis to transfer peptides or small molecules across membranes.

15

mTOR

A large protein kinase involved in mammalian cell signalling.

16

Single-pass transmembrane protein

A membrane protein in which the polypeptide chain crosses the lipid bilayer only once.

17

Liposome

An artificial phospholipid bilayer vesicle formed from an aqueous suspension of phospholipid molecules.

18

Serine protease

A type of protease that has a reactive serine in the active site.

19

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.

20

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.

21

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.

22

Caspase

An intracellular protease that is involved in mediating the intracellular events of apoptosis.

23

Mitochondrial precursor proteins

Proteins first fully synthesized in the cytosol and then translocated into mitochondrial subcompartments as directed by 1 or more signal sequences.

24

Cohesin

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.