Molecular Cell Bio-Final

Protein kinase C (PKC)

A Ca2+-dependent protein kinase that is activated by diacylglycerol.

Lignin

A complex network of phenolic compounds that is an abundant polymer in secondary cell walls.

TOR or mTOR (Target of Rapamycin)

A crucial signaling protein in the PI-3-kinase-Akt signaling pathway, so named because it is the target of rapamycin.

Blebbing

A distinct form of membrane protrusion that is often observed when cells are cultured on a pliable extracellular matrix substrate.

Wnt proteins

A family of secreted signal molecules that act as local mediators and morphogens during development; they were initially discovered as the products of the Wingless gene in flies and the Int1 gene in mice.

Bivalent

A four-chromatid structure that arises from the close juxtaposition of homologs as prophase progresses.

Rho family protein

A group of closely related monomeric GTPases that includes Cdc42, Rac, and Rho.

Rho family

A group of monomeric GTPases that regulate both the actin and microtubule cytoskeletons.

Hedgehog proteins

A group of secreted signal molecules that act as local mediators and morphogens during development and whose effects are mediated through the cell-surface receptor Patched and its binding partner Smoothened.

phosphoinositide 3-kinase (PI 3-kinase)

A kinase that is involved in intracellular signaling pathways activated by cell-surface receptors and that phosphorylates inositol phospholipids at the 3 position of the inositol ring.

Protofilament

A linear chain of protein subunits joined end to end, which associates laterally with other such chains to form cytoskeletal components.

Cadherin

A member of a family of proteins that mediate Ca2+-dependent cell-cell adhesion in animal tissues.

Dynein

A member of the family of motor proteins that move along microtubules by walking toward the minus end.

Cdk

A member of the family of protein kinases that have to be complexed with a cyclin protein in order to act

Kinesin

A motor protein that moves along microtubules by walking toward the plus end.

SH2 domain

A protein domain that is homologous to a region in Src, is present in many proteins, and binds to a short amino acid sequence containing a phosphotyrosine.

Gap junction

A protein structure that creates direct channels from the cytoplasm of one cell to the cytoplasm of an adjacent cell.

Kinase cascade

A signal relay chain involving multiple protein kinases, each of which is activated by phosphorylation and then phosphorylates the next protein kinase in the sequence.

Wnt/B-catenin pathway

A signaling pathway activated by Wnt binding to both the Frizzled receptor and the LRP co-receptor.

G0

A specialized, nondividing state that cells enter by partly disassembling their cell-cycle control system and exiting from the cell cycle.

Cubitius interruptus (Ci)

A target of Hedgehog signaling, this gene regulatory molecule is a fulllength gene activator in the presence of Hedgehog and a partially proteolyzed gene repressor in its absence.

MAP kinase module

A three-component signaling module used in various signaling pathways in eukaryotic cells.

Cell-cycle control system

A timing mechanism that triggers events of the cell cycle in a set sequence, using feedback from the processes it controls to ensure that one stage is complete before the next one begins.

Adaptation (desensitization)

Alteration of sensitivity following repeated stimulation reducing a cell's response to that level of stimulus.

Bcl2 protein death-inducing signaling complex (DISC)

An assembly of several proteins, including initiator caspases, on the cytosolic portion of the Fas death receptor.

Matrix metalloprotease

An extracellular proteolytic enzyme that degrades proteins such as collagen, laminin, and fibronectic in a Ca2+ - or Zn2+ -dependent reaction.

Chiasma

An inter-homolog connection that arises from an individual crossover event between nonsister chromatids.

Adherens junction

Anchoring junction that connects actin filaments in one cell to those in the next cell.

Intrinsis pathway

Apoptotic program that depends on the release into the cytosol of proteins from the mitochondrial intermembrane space.

Extrinsis pathway

Apoptotic program triggered by the binding of an extracellular signal protein.

Adhesion belt

Beltlike anchoring junction that encircles the apical end of an epithelial cell and attaches it to the adjoining cells.

Cellulose microfibril

Bundle of about 30 long, linear chains of covalently linked glucose residues, all with the same polarity, organized in an overlapping parallel array.

Axoneme

Bundle of microtubules and associated proteins that forms the core of a cilium or flagellum in a eukaryotic cell and is responsible for their movements.

Ryanodine receptor

Ca2+-release channel in the ER membrane that is activated by Ca2+ binding in the absence of IP3.

Contact-dependent signaling

Cell-cell communication in which the signal molecule remains bound to the signaling cell and only influences cell that physically touch it.

Death receptor

Cell-surface molecule that triggers apoptosis when bound by an extracellular signal protein.

Enzyme-coupled receptor

Cell-surface receptor in which the cytoplasmic domain either has enzymatic activity itself or is associated with an intracellular enzyme.

Tyrosine-kinase-associated receptor

Cell-surface receptor that activates a tyrosine kinase that is noncovalently bound to the receptor.

G-protein-coupled receptor (GPCR)

Cell-surface receptor that associates with an intracellular G protein upon activation by an extracellular ligand.

Receptor tyrosine kinase (RTK)

Cell-surface receptor that when activated by ligand binding adds phosphates from ATP to tyrosine side chains in its own cytoplasmic domain.

Centrosome

Centrally located organelle of animal cells that after duplication organizes each spindle pole during mitosis.

Contractile ring

Circular band containing actin and myosin that forms under the surface of animal cells undergoing cell division and contracts to pinch the two daughter cells apart.

Fibroblast

Common cell type in connective tissue that secretes an extracellular matrix rich in collagen and other extracellular matrix macromolecules.

Plasmodesmata

Communicating cell-cell junctions in plants in which a channel of cytoplasm lined by plasma membrane connects two adjacent cells through a small pore in their cell walls.

Interaction domain

Compact protein module that binds to a particular structural motif in another protein (or lipid) molecule with which the signaling protein interacts.

Cohesin

Complex of proteins that holds sister chromatids together along their length until they separate at mitosis.

Condensin

Complex of proteins that uses the energy of ATP hydrolysis to promote the compaction and resolution of sister chromatids.

Syncytium

Cytoplasm containing many nuclei enclosed by a single plasma membrane.

Focal adhesion kinase (FAK)

Cytoplasmic protein tyrosine kinase present at cell-matrix junctions in association with the cytoplasmic tails of integrins.

Anchorage dependence

Dependence of cell growth, proliferation, and survival on attachment to a substratum.

Polarized

Describes a structural property of epithelial sheets, and their individual cells, which have one surface attached to the basal lamina below and the opposite surface exposed to the medium above.

Apical

Describes the tip of a cell; for an epithelial cell, it is the exposed free surface, opposite to the surface attached to the basal lamina.

Cytokinesis

Division of the cytoplasm of a plant or animal cell into two.

Telomere

End of a chromosome, associated with a characteristic DNA sequence that is replicated in a special way.

Phospholipase C-B (PLCB)

Enzyme bound to the cytoplasmic surface of the plasma membrane that converts membrane PI(4,5)P2 to diacylglycerol and IP3.

Cyclic AMP phosphodiesterase

Enzyme that hydrolyzes cyclic AMP to adenosine 5'-monophosphate (5'-AMP).

GPCR kinase (GRK)

Enzyme that participates in desensitization of GPCRs by phosphorylating them after they have been activated by ligand binding.

Cyclic-AMP-dependent protein kinase (PKA)

Enzyme that phosphorylates target proteins in response to a rise in intracellular cyclic AMP.

Protein kinase

Enzyme that transfers the terminal phosphate group of ATP to a specific amino acid of a target protein.

Filopodium

Essentially a one-dimensional structure that protrudes from a cell and contains a core of long, bundled actin filaments.

Laminin

Extracellular matrix protein found in basal laminae, where it forms a sheetlike network.

Fibronectin

Extracellular matrix protein that binds to cell-surface integrins to promote adhesion of cells to the matrix and to provide guidance to migrating cells in developing tissues.

Survival factor

Extracellular signal molecule that inhibits apoptosis.

Mitogen

Extracellular substance that stimulates cell division.

Growth factor

Extracellular substance that stimulates cell growth.

Collagen

Fibrous protein rich in glycine and proline that, in its many forms, is a major component of the extracellular matrix and connective tissues.

Telophase

Final stage of mitosis in which the two sets of separated chromosomes decondense and become enclosed by nuclear envelopes.

Lamellipodium

Flattened, two-dimensional protrusion of membrane, supported by a meshwork of actin filaments, that is extended from the leading edge of crawling epithelial cells, fibroblasts, and some neurons.

Apoptosis

Form of cell death that leads to fragmentation of the DNA, shrinkage of the cytoplasm, membrane changes, and cell death, without lysis or damage to neighboring cells.

Stimulatory G protein (Gs)

G protein that activates adenylyl cyclase and thereby increases cyclic AMP concentration.

E2F protein

Gene regulatory factor that is activated by G1-Cdk complexes in animal cells and binds to specific DNA sequences in the promoters of genes that encode proteins required for S-phase entry.

Glycosaminoglycan (GAG)

General name for a long, linear, highly charged polysaccharide-composed of a repeating pair of sugars, one of which is always an amino sugar-that is found covalently linked to a protein core in the extracellular matrix.

Receptor

General term for a protein that binds a specific extracellular molecule (ligand) and initiates a response in the cell.

Cycle-Cdk complex

General term for one of the several protein assemblies that form periodically during the cell cycle as the level of cyclin increases, and partially activate the cyclin-dependent kinase component.

Elastin

Hydrophobic protein that forms extracellular exensible fibers that give tissues their stretchability and resilience.

Steroid hormone

Hydrophobic signaling molecule with a characteristic four-ringed structure derived from cholesterol.

Metaphase plate

Imaginary plane midway between the spindle poles in which chromosomes are positioned at metaphase.

Transforming growth factor-B(TGFB) superfamily

Large family of structurally related, secreted, dimeric proteins that act as hormones and local mediators to control a wide range of biological functions in all animals.

origin recognition complex (ORC)

Large protein complex that is bound throughout the cell cycle at origins of replication in eukaryotic chromosomes.

NFkB proteins

Latent gene regulatory proteins that are present in most cells in both animals and plants and are central to many stress, inflammatory, and innate immune responses.

Rhodopsin

Light-sensitive GPCR in rod photoreceptor cells of the retina.

Homophilic

Like-to-like protein interaction in which a molecule on one cell binds to an identical, or closely related, molecule on an adjacent cell.

Flagellum

Long, hairlike protrusion from the surface of a eukaryotic cell whose undulations drive the cell through a liquid medium.

Myofibril

Long, highly organized bundle of actin, myosin, and other proteins in the cytoplasm of muscle cells that contracts by a sliding-filament mechanism.

Tight junction

Main type of occluding junction in vertebrates; it seals adjacent epithelial cells together, preventing the passage of most dissolved molecules from one side of the epithelial sheet to the other.

Spindle assembly checkpoint

Mechanism ensuring that cells do not enter anaphase until all chromosomes are correctly bi-oriented on the mitotic spindle.

Selectin

Member of a family of cell-surface carbohydrate-binding proteins that mediate transient, Ca2+-dependent cell-cell adhesion in the bloodstream, for example, between white blood cells and the endothelium of the blood vessel wall.

Neurofilament

Member of a family of intermediate filaments that are found in high concentrations along the axons of vertebrate neurons.

Astral microtubule

Microtubule that radiates outward from the spindle pole and contacts the cell cortex, helping to position the spindle in the cell.

Interpolar microtubule

Microtubules that overlap in the spindle midzone and interact via their plus ends, generating an antiparallel array.

Extracellular signal molecule

Molecule from outside the cell that communicates the behavior or actions of other cells in the environment and elicits an appropriate response.

microtubule flux

Movement of tubulin subunits toward the spindle poles as a result of addition of new subunits at the plus ends of microtubules and their disassemble at minus ends.

Cyclin

One of a family of proteins that rise and fall in concentration in step with the eukaryotic cell cycle, thereby regulating the activity of the crucial protein kinases that control progression through the cell cycle.

JAK-STAT signaling pathway

One of several intracellular signaling pathways that leads from cell-surface receptors to the nucleus, it is distinguished by providing one of the more direct routes.

Replicative cell senescence

Phenomenon observed in primary cell cultures as they age, in which cell proliferation slows down and finally halts.

Caspase

Protease that has a cysteine at its active site and cleaves its target proteins at specific aspartic acids.

Separase

Protease whose activation at the end of metaphase results in the cleavage of cohesin and the separation of sister chromatids.

Gamma-tubulin ring complex

Protein assembly containing a special form of tubulin, along with other proteins, that is an efficient nucleator of microtubule growth.

Arp2/3 complex

Protein assembly that nucleates actin filament growth from the minus end, allowing rapid growth at the plus end and forming a treelike web of filaments.

trimeric GTP-binding protein (G protein)

Protein composed of three subunits, one of which is activated by the binding of GTP.

Pleckstrin homology (PH) domain

Protein domain found in intracellular signaling proteins by which they bind to inositol phopholipids phosphorylated by PI 3-kinase.

Ca2+/calmodulin-dependent kinase (CaM-kinase)

Protein kinase whose activity is regulated by the binding of Ca2+-activated calmodulin, and which indirectly mediates the effects of Ca2+ by phosphorylation of other proteins.

Guanine nucleotide exchange factor (GEF)

Protein that binds to a GTP-binding protein and activates it by stimulating release of tightly bound GDP, thereby allowing it to bind GTP.

GTPase-activating protein (GAP)

Protein that binds to a GTP-binding protein and inactivates it by stimulating its GTPase activity so that its bound GTP is hydrolyzed to GDP.

Geminin

Protein that binds to and inhibits a key component of the prereplicative complex.

CRE-binding (CREB) protein

Protein that binds to the cyclic AMP response elements found in the regulatory region of many genes activated by cyclic AMP.

Regulator of G protein signaling (RGS)

Protein that is an a-subunit-specific GTPase-activating protein (GAP).

Scaffold protein

Protein that organizes groups of interacting intracellular signaling proteins into signaling complexes.

Notch Pathway

Receptor protein involved in what may be the most widely used signaling pathway in animal development; its ligands are cell-surface proteins such as Delta

Secondary cell wall

Rigid cell-covering laid down in layers inside the initial covering once cell growth has stopped.

IP3

Second messenger that is released from a phospholipid in the plasma membrane and diffuses to the ER, where it opens Ca2+-release channels.

Centriole

Short cylindrical array of microtubules, a pair of which are embedded in the major microtubule-organizing center of an animal cell.

Paracrine signaling

Short-range cell-cell communication via secreted local mediators that act on adjacent cells.

Second messenger

Small molecule that is formed in the cytosol, or released into it, in response to an extracellular signal and that helps to relay the signal to the interior of the cell.

Neurotransmitter

Small signal molecule secreted by the presynaptic nerve cell at a chemical synapse to relay the signal to the postsynaptic cell.

Endocrine cell

Specialized animal cell that secretes a hormone into the blood.

Cell cortex

Specialized layer of cytoplasm on the inner face of the plasma membrane, rich in actin filaments.

Anaphase B

Stage of mitosis in which the spindle poles move apart.

Midbody

Structure formed at the end of cleavage that can persist for some time as a tether between the two daughter cells

Phragmoplast

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.

Cytoskeleton

System of protein filaments in the cytoplasm of a eukaryotic cell that gives the cell its shape and the capacity for directed movement.

Restriction point

The checkpoint in the cell cycle that governs the cell's commitment to enter S phase.

Synaptonemal complex

The closely packed array of transverse filaments that links the axial cores of paired homologs.

M-Cdk

The cyclin-Cdk complex responsible for stimulating entry into mitosis at the G2/M checkpoint.

Nondisjunction

The failure of homologs to separate properly.

Metaphase-to-Anaphase transition

The final major checkpoint in the cell cycle, where the control system stimulates sister-chromatid separation, leading to the completion of mitosis and cytokinesis.

Ras

The founding member of a superfamily of monomeric GTPases that help to relay signals from cell-surface receptors to the nucleus.

Turgor pressure

The large internal hydrostatic pressure that develops in plant cells due to the osmotic imbalance between the cell interior and the fluid in the plant cell wall.

Ephrins

The largest class of cell-surface-bound extracellular signal proteins.

Interphase

The long period of the cell cycle between one mitosis and the next.

Keratin

The most diverse intermediate filament family, with about 20 types found in human epithelial cells and 10 more specific to hair and nails.

Myosin

The motor protein in muscle that generates the force for muscle contraction.

Cell Cycle

The orderly sequence of events by which a cell duplicates its contents and divides in two.

G1 Phase

The phase of the eukaryotic cell cycle between the end of cytokinesis and the start of DNA synthesis.

Treadmilling

The process by which a polymeric protein filament is maintained at constant length by addition of protein subunits at one end and loss of subunits at the other.

Dynamic instability

The property of sudden conversion from growth to shrinkage, and vice versa, in a protein filament such as a microtubule or an actin filament.

ATM

The protein kinase that is initially activated in response to x-ray-induced DNA damage and is defective in patients with ataxia telangiectasia.

anaphase-promoting complex or Cyclosome (APC/C)

The ubiquitin ligase that promotes the destruction of a specific set of proteins, thereby promoting the separation of sister chromatids and the completion of M phase.

Meiosis I

The unique form of cell division that segregates homologs.

Primary cell wall

Thin and exensible cell-covering on new plant cells that can accommodate their growth.

Basal lamina

Thin mat of extracellular matrix that separates epithelial sheets, and many other types of cells such as muscle or fat cells, from connective tissue.

Desmosome

Type of anchoring junction that links the intermediate filaments in two adjoining cells.

Calmodulin

Ubiquitous calcium-binding protein whose interaction with other proteins are governed by changes in intracellular Ca2+ concentration.

Connexon

Water-filled pore in the plasma membrane formed by a ring of six protein subunits, which link to an identical assembly in an adjoining cell to form a continuous channel between the two cells.

Apoptosome

Wheel-like assembly composed of seven copies of the Apaf1/cytochrome c complex.

Executioner caspase

When cleaved by an initiator caspase, this protease is activated and participates in the widespread cleavage events that kill the cell.