A biological cell is a membrane-bounded basic unit of living organization. In a cell-level experiment it can be an experimental unit, provided that treatment assignment and relevant interactions are handled at that level.
The shared architecture of cellular life combines a selective cell membrane, internal cytoplasm, inherited information in DNA, and ribosomes that assemble proteins. Metabolism supplies transformations of matter and energy needed for maintenance and growth. These components form a coupled system: a boundary retains useful molecules, enzymes organize chemical reactions, and inherited information supports rebuilding the machinery. See Clark, Douglas and Choi, Biology 2e: prokaryotic cells.
A worked structural comparison: in a typical prokaryote, DNA occupies a region without a surrounding cell nucleus; in a typical nucleated eukaryote, much of the DNA lies inside a membrane-bounded cell nucleus. Both still have a cell membrane, cytoplasm and ribosomes. The extra boundary compartmentalizes processes; it does not create a different basic principle of living organization. See Clark, Douglas and Choi, Biology 2e: eukaryotic cells.
Shared cellular architecture with different DNA compartmentalization
. Original simplified schematics of a prokaryote and a nucleated eukaryote. Colors identify corresponding components; sizes and component counts are illustrative, and additional structures are omitted. Details.
Shared architecture describes cellular life and its developmental machinery, rather than requiring every specialized biological cell to retain every component. A mature mammalian red blood cell, for example, lacks a cell nucleus, although it develops from nucleated precursors. See Clark, Douglas and Choi, Biology 2e: components of blood. This distinction makes cellular unity compatible with striking specialization.
An appendage used for movement or other functions. Bacterial flagella are driven by a bacterial flagellar motor; their construction differs from eukaryotic motile cilia.
A cellular projection whose structure and functions differ from the bacterial flagellar apparatus. Motile cilia can move fluid; a transport estimate must compare advection with diffusion.
The account that organisms are organized from biological cells and that cellular continuity is fundamental to their growth and reproduction. Its nineteenth-century formulation developed alongside changing accounts of cell division.
An immune-cell lineage associated with antibody responses. Lineage-specific proliferation and clonal expansion should be distinguished from changes in a mixed sample.
An innate cytotoxic lymphocyte whose activation integrates inhibitory and activating signals. Reduced class-I display can remove inhibitory signalling, but is not by itself a universal guarantee of killing.
Preferential delivery, recycling or removal of membrane components in different cellular domains. Domain-specific traffic converts positional information into unequal membrane growth and composition.
A cardiac muscle cell. Embryonic differentiation and contractile activity are compatible with continued proliferation; adult cell-cycle re-entry does not necessarily entail completed division.
Enlargement of individual cardiac muscle cells, distinct from an increase in cardiomyocyte number through completed division.
Neighbour-dependent selection among cell populations in which relatively less-fit cells are lost or displaced. Homogeneous toxicity or slower autonomous growth alone does not establish competitive elimination.
A proliferative descendant population that expands cell output before differentiation. The number of divisions and capacity for reversal depend on tissue and context.
A cellular phenotype attributable to the affected cell's own genotype or state under the tested conditions. Mosaic experiments distinguish this from effects transmitted through neighbouring cells or the environment.
A bacteriocyte is a specialized host cell containing bacterial symbionts. The intracellular environment and transmission route shape selection on both partners.
A reticulate body is the growth-associated form in the chlamydial developmental cycle. genome replication alone does not establish successful production of infectious elementary bodies.
An elementary body is the infectious form in the chlamydial developmental cycle. Environmental persistence during transmission is distinct from productive extracellular replication.
A chlamydial inclusion is the membrane-bound intracellular compartment supporting chlamydial development. Host trafficking interactions and nutrient access are regulated there.
A lipid droplet is a cellular lipid-storage structure. Delivery of an engineered fatty acid into storage can be limited independently of the pathway that synthesizes it.
A membrane contact site closely apposes distinct membranes without fusing them. Demonstrating apposition establishes architecture, while transfer or signaling requires separate functional evidence.
An endoplasmic reticulum-mitochondrial contact site brings ER and mitochondrial membranes close while preserving their separate compartments. Specific contacts can contribute to calcium handling, lipid exchange and organelle organization.
A Chinese hamster ovary cell is a mammalian cell type widely used in recombinant-protein production. Product glycosylation, assembly and quality depend on the engineered line and culture process.
HAT selection uses hypoxanthine, aminopterin and thymidine to distinguish cells able to maintain nucleotide supply through salvage metabolism under de novo synthesis blockade. In a conventional hybridoma scheme it selects suitable fusion products, not antigen specificity.
A myeloma is a malignancy of the plasma-cell lineage. Selected cultured myeloma lines provide an immortal fusion partner in hybridoma production; their metabolic selection properties depend on the particular line.
A B lymphocyte belongs to the antibody-producing lineage of the adaptive immune system. Recovery of an antigen-binding clone does not alone establish a useful therapeutic antibody or an immortal production line.
A lymphocyte recovered from within a tumour specimen. Presence in a specimen does not alone establish effective recognition or killing of malignant cells.
A stromal cell of the pancreas that can adopt activated states and contribute to extracellular matrix and metabolic interactions in pancreatic disease.
A lymphocyte using a T-cell receptor for antigen recognition. Distinct populations have cytotoxic, helper, regulatory and memory functions.
A coreceptor usually associated with recognition of peptide–MHC-class-II complexes. CD4 T-cell populations coordinate and regulate immune responses in addition to other context-dependent activities.
A T-cell costimulatory receptor. Its interaction with B7 ligands on activated antigen-presenting cells contributes to naive-cell priming.
A coreceptor associated with recognition of peptide–MHC-class-I complexes by cytotoxic T cells. It contributes to binding and signalling without replacing T-cell-receptor specificity.
An antigen-presenting immune cell that can help initiate T-cell responses. Antigen uptake alone does not establish effective activating presentation.
A myeloid population defined partly by its ability to suppress immune responses, particularly in disease-associated settings such as cancer.
A T-cell population with immune-suppressive functions that can restrain both pathological inflammation and antitumour responses.
A cell lining a blood or lymphatic vessel. Endothelial state influences barrier function, perfusion and interactions with circulating cells.
A macrophage within or associated with a tumour microenvironment. Its contribution to invasion, vascular remodelling or immunity depends on the particular functional state.
An innate immune cell that can phagocytose material and regulate tissue and immune responses. Its behaviour varies with local signals and cellular history.
A fibroblast in a tumour-associated state. Some functions support tumour progression while other fibroblast populations or functions can restrain it; the label alone does not establish the causal effect.
A connective-tissue cell with roles in extracellular matrix production and tissue organisation. Fibroblast populations and activation states are heterogeneous.
An increase in cellular biomass or size. It differs from cell proliferation, which increases the number of cells.
A cell participating in an organised epithelial layer, with context-dependent polarity, adhesion and barrier or transport functions.
Madin-Darby canine kidney cell, used in three-dimensional epithelial cyst and polarity assays.
A keratinocyte in the basement-membrane-associated compartment of a stratified epithelium. Basal position does not establish that every such cell is actively dividing.
A specialized secretory cell normally found at the base of mammalian small-intestinal crypts. Its local antimicrobial and niche-support roles do not imply that all intestinal stem-cell systems require a Paneth-cell arrangement.
A specialized epithelial sensory cell population with characteristic apical morphology and context-dependent signalling roles.
A specialized intestinal epithelial cell that senses local conditions and releases signalling products, including hormones.
A specialized mucus-secreting epithelial cell, present in the intestinal lining and other mucosal tissues.
An absorptive epithelial cell of the intestinal lining. Enterocyte-lineage progenitors and terminally differentiated villus enterocytes need not have the same regenerative potential.
Partition of one cell into descendant cells. Copying and allocating inherited material must be coordinated with physical separation, but nuclear division and cytokinesis are distinct events.
A biological cell division that produces two daughter cells. It is an asexual reproduction mechanism in many unicellular organisms and is distinct from the exchange or recombination of genetic material during sexual processes.
The endomembrane system comprises functionally connected internal membranes such as the endoplasmic reticulum, Golgi apparatus, endosomes and lysosomes, together with their transport carriers. Connections through carrier traffic differ from direct continuity of the membrane sheets.
Ordinary vesicle budding and fusion preserve which side of a membrane a protein domain faces: a cytoplasmic domain remains cytoplasmic, and a luminal domain remains luminal. Invagination can enclose previously external space without transporting its contents through a bilayer. The endoplasmic reticulum lumen is continuous with the space between the two nuclear envelope membranes; it is not the chromosome-containing nucleoplasm. Any proposed evolutionary remodelling must account for these distinct spaces and the membrane connections between them.
Cell adhesion is attachment of a biological cell to another cell or to its surroundings through molecular interactions. Adhesion strength and turnover help determine how cells transmit forces and rearrange.
A cell-cell junction coupling adhesion to the cytoskeleton. It can transmit mechanical load while being remodelled during epithelial movements.
A focal adhesion is a multiprotein connection between integrins and the actin cytoskeleton. It can transmit traction and change its assembly in response to loading.
A class of biological cells distinguished by characteristic structure, function or molecular state. Comparing mixed biological tissues can confound changes within a cell type with changes in the abundance of that class.
subcellular localization is the distribution of a component among cellular regions or compartments. Changing localization can change a protein's partners even when its total abundance is constant.
Isolated blastomeres are reapposed in chosen combinations to test induction. Reciprocal wild-type and mutant combinations can separate a signalling-cell defect from a responding-cell defect.
An early posterior Caenorhabditis elegans blastomere that contacts EMS and provides inductive information required for normal endoderm specification.
The sister of the E blastomere in Caenorhabditis elegans. Its descendants include muscle and part of the pharynx; it is not the normal intestinal founder.
The founder of the Caenorhabditis elegans intestinal lineage. Following its descendants distinguishes failure of endoderm specification from a failure of terminal differentiation.
The early Caenorhabditis elegans blastomere that divides into MS and E. Its daughters normally produce predominantly mesodermal derivatives and the intestine, respectively.
A spatial asymmetry of cellular organisation, including distinct apical and basal domains, that can influence division, signalling and lineage allocation.
Growth concentrated at a selected part of the biological cell surface. Spatial selection can be controlled at transport, vesicle docking or fusion rather than only by directed vesicle motion.
Coordinated asymmetry within the plane of a tissue, distinct from the apical-basal axis. Not every case of planar polarization uses the same molecular pathway.
A group of interacting polarity regulators including PAR-3, PAR-6 and atypical protein kinase C. Its organization links cortical domains to junctional and morphogenetic behaviour.
Organization of epithelial cells into distinct apical and basolateral domains. Individual apical identity and coordination of apical surfaces into a shared tissue lumen are related but distinct properties.
Basolateral polarity regulators including Scribble, Discs large and Lethal giant larvae. Their interactions oppose inappropriate apical-domain expansion while supporting other tissue-specific functions.
Apical-domain regulators organized around Crumbs-family proteins and associated scaffolds. Tissue-specific interactions and dosage influence apical membrane organization.
A regulated form of cell death. Measuring it helps distinguish failed cell specification from selective loss of an already specified population.
A BCL-2-family effector promoting mitochondrial outer-membrane permeabilization during apoptosis. Its activation differs from merely increasing expression of an apoptotic gene.
A proapoptotic BH3-only BCL-2-family protein that can be induced by p53. Its effects depend on the survival-protein context.
A proapoptotic BH3-only BCL-2-family protein induced in some p53 responses, contributing to mitochondrial apoptosis.
A rearrangement in which cells insert between neighbours, altering tissue shape and adjacency without requiring cell division.
Rearrangement in which cells move between neighbours along the mediolateral axis, contributing to convergence and extension of a tissue.
An increase in the number of biological cells through cell division. Cell number and tissue volume are distinct measurements because cell size and packing can change.
Expansion of a lymphocyte lineage sharing clonal ancestry. Detection of a clone is not by itself proof of aggressive malignant disease.
Reduced proliferation or movement in response to cellular contacts under a specified context. Tissue growth control involves additional signals beyond contact alone.
Cell migration is movement of a biological cell relative to its surroundings. In crawling cells, contact forces with a substrate can propel the cell, while chemotaxis can bias its direction in response to a chemical gradient.
Displacement of cells with bulk tissue motion. Subtracting the surrounding flow is needed to distinguish autonomous crawling from passive transport.
Contact guidance is a directional influence of physical structures, such as aligned fibres or grooves, on cell migration. It can organize trajectories without an imposed soluble concentration gradient.
Haptotaxis is directed cell migration along spatial variation of an immobilized adhesive or guidance cue. It differs from guidance by a soluble chemoattractant field.
Durotaxis is biased cell migration associated with spatial variation in substrate stiffness. Distinguish a directional bias from changes in speed, attachment or survival on different substrates.
Chemokinesis is a change in motility associated with a chemical stimulus without a directional bias toward or away from its source. Measure speed and persistence separately from directional chemotaxis.
A membrane bleb is a rounded protrusion formed when the cell membrane locally detaches from or loses support by the cell cortex. Pressure expands the initially cortex-poor region; cortical reassembly can then stabilize or retract it.
A lamellipodium is a broad, thin, actin-rich protrusion at a cell edge. Actin polymerization pushes the cell membrane, but net advance also depends on mechanical coupling to the environment.
In collective cell migration, neighbouring biological cells move with coordinated trajectories while retaining interactions that influence their motion. Mechanical coupling, contact-dependent signals and soluble cues can each contribute. A coherent group need not consist of identically behaving cells: leaders and followers may perform different roles.
A quantitative measure of coordinated cell velocities. A common external force can create correlation without proving direct cell-to-cell transmission of guidance.
Contact inhibition of locomotion is a contact-triggered change of protrusions and movement direction. It is distinct from contact inhibition of proliferation. In neural crest experiments, cell collisions caused protrusion collapse and repolarization; blocking noncanonical Wnt signalling disrupted the response.[ref]
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