This glossary of cell biology is a list of definitions of terms and concepts commonly used in the study of cell biology and related disciplines in biology, including developmental biology, genetics, microbiology, molecular biology, and biochemistry.

It is intended as introductory material for novices; for more specific and technical detail, see the article corresponding to each term. For related terms, see Glossary of biology, Glossary of genetics, Glossary of developmental biology, Glossary of virology, and Glossary of chemistry.


adenosine diphosphate (ADP)
adenosine monophosphate (AMP)
adenosine triphosphate (ATP)
amino acid
Any of a class of organic compounds whose basic structural formula includes a central carbon atom bonded to amine and carboxyl functional groups and to a variable side chain. Out of nearly 500 known amino acids, a set of 20 are coded for by the standard genetic code and incorporated into long polymeric chains as the building blocks of peptides and hence of polypeptides and proteins. The specific sequences of amino acids in the polypeptide chains that form a protein are ultimately responsible for determining the protein's structure and function.
The stage of mitosis and meiosis that occurs after metaphase and before telophase, when the replicated chromosomes are segregated and each of the sister chromatids are moved to opposite sides of the cell.


binary fission


cell biology

Also cellular biology.

The branch of biology that studies the structures, functions, processes, and properties of biological cells, the self-contained units of life common to all living organisms.
cell compartmentalization
The subdivision of the interior of a cell into distinct, usually membrane-bound compartments, including the nucleus and organelles (endoplasmic reticulum, mitochondria, chloroplasts, intracellular vesicles, etc.), a defining feature of the Eukarya.[1]
cell culture
cell cycle
cell division
cell signaling
cell wall
cellular differentiation
cellular reprogramming
The conversion of a fully differentiated cell from one tissue-specific cell type to another. This involves dedifferentiation to a pluripotent state; an example is the conversion of mouse somatic cells to an undifferentiated embryonic state, which relies on the transcription factors Oct4, Sox2, Myc, and Klf4.[2]
A cylindrical organelle composed of microtubules, present only in certain eukaryotes. A pair of centrioles migrate to and define the two opposite poles of a dividing cell where, as part of a centrosome, they initiate the growth of the spindle apparatus.
A nuclear DNA molecule containing part or all of the genetic material of an organism. Most eukaryotes have multiple chromosomes composed of very long linear strands of DNA coiled and condensed by histone proteins into chromatin. Chromosomes are most easily distinguished and studied in their completely condensed forms, which only occur during cell division. The circular DNA genomes of bacteria and some viruses are also sometimes called chromosomes, though they are not composed of chromatin and are not contained within a nucleus.
citric acid cycle
A multinucleate mass of cytoplasm bounded by a cell wall and resulting from continuous cytoplasmic growth and repeated nuclear division without cytokinesis, found in some species of algae and fungi, e.g. Vaucheria and Physarum.[1]
coenzyme A
cyclic adenosine monophosphate (cAMP)
The final stage of cell division in both mitosis and meiosis, usually immediately following the division of the nucleus, during which the cytoplasm of the parent cell is cleaved and divided approximately evenly between the two daughter cells. In animal cells, this process occurs by the closing of a microfilament contractile ring in the equatorial region of the dividing cell. Contrast karyokinesis.
The study of the morphology, processes, and life history of living cells, particularly by means of light and electron microscopy.[1] The term is also sometimes used as a synonym for the broader field of cell biology.
See lysis.
cytoplasmic streaming

Also protoplasmic streaming and cyclosis.

The flow of the cytoplasm inside a cell, driven by forces exerted upon cytoplasmic fluids by the cytoskeleton. This flow functions partly to speed up the transport of molecules and organelles suspended in the cytoplasm to different parts of the cell, which would otherwise have to rely on passive diffusion for movement. It is most commonly observed in very large eukaryotic cells, for which there is a greater need for transport efficiency.

Also hyaloplasm.

The soluble phase of the cytoplasm, in which small particles such as ribosomes, proteins, nucleic acids, and many other molecules are suspended or dissolved, excluding larger structures and organelles such as mitochondria, chloroplasts, lysosomes, and the endoplasmic reticulum.[1]


deoxyribonucleic acid (DNA)
A polymeric nucleic acid molecule composed of a linear chain of deoxyribonucleotides, each of which incorporates one of four canonical nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). DNA is most often found in double-stranded form, where two chains or strands are paired together by hydrogen bonds between the individual nucleotides of each strand. This structure commonly occurs in the shape of a double helix. By storing and encoding genetic information in the sequence of its nucleotides, DNA serves as the universal molecular basis of biological inheritance and the fundamental template from which all proteins, cells, and living organisms are constructed.
The failure of homologous chromosomes that have synapsed normally during pachynema to remain paired during diplonema. Desynapsis is usually caused by the improper formation of chiasmata.[3] Contrast asynapsis.
developmental biology
In meiosis, the fifth and final substage of prophase I, following diplonema and preceding metaphase I. During diakinesis, the chromosomes are further condensed, the two centrosomes reach opposite poles of the cell, and the spindle apparatus begins to extend from the poles to the equator.[3]

Also diplotene stage.

In meiosis, the fourth of the five substages of prophase I, following pachynema and preceding diakinesis. During diplonema, the synaptonemal complex disassembles and the paired homologous chromosomes begin to separate from one another, though they remain tightly bound at the chiasmata where chromosomal crossover has occurred.
See deoxyribonucleic acid.


electron transport chain
Any membrane surrounding an intracellular organelle or vesicle, e.g. that of the endoplasmic reticulum, Golgi apparatus, lysosome, vacuole, nucleus (the nuclear envelope), etc.[1]
endoplasmic reticulum (ER)
To artificially remove the nucleus from a cell, e.g. by micromanipulation in the laboratory or by destroying it through irradiation with ultraviolet light, rendering the cell anucleate.[1]
1.  (protein complex) An intracellular multi-protein complex which serves the function of degrading various types of RNA molecules.
2.  (vesicle) A type of membrane-bound extracellular vesicle produced in many eukaryotic cells by the inward budding of an endosome and the subsequent fusion of the endosome with the plasma membrane, causing the release of the vesicle into various extracellular spaces, including biological fluids such as blood and saliva, where they may serve any of a wide variety of physiological functions, from waste management to intercellular signaling.
Outside the plasma membrane of a cell or cells; i.e. located or occurring externally to a cell. Contrast intracellular; see also intercellular.
extracellular matrix (ECM)


fatty acid


A haploid cell that is the meiotic product of a progenitor germ cell and the final product of the germ line in sexually reproducing multicellular organisms. Gametes are the means by which an organism passes its genetic information to its offspring; during fertilization, two gametes (one from each parent) are fused into a single diploid zygote.
germ cell
Any cell that gives rise to the gametes of a sexually reproducing organism. Germ cells are the vessels for the genetic material which will ultimately be passed on to the organism's descendants and are usually distinguished from somatic cells, which are entirely separate from the germ line.
glucogenic amino acid
gluconeogenesis (GNG)
The chain of metabolic reactions that results in the generation of glucose from some non-carbohydrate carbon substrates, including the glucogenic amino acids. It is one of two primary pathways used by most animals to maintain blood sugar levels (the other being glycogenolysis), especially during periods of fasting, starvation, and intense exercise.
Any chemical compound in which a carbohydrate molecule is covalently bonded to another molecule containing a hydroxyl group (including other carbohydrates) via one or more C
glycosidic bonds. When both molecules are carbohydrates, the glycoside is a disaccharide or polysaccharide.[1]
glycosidic bond
The attachment of an oligosaccharide (e.g. glucose) to an asparagine residue within a peptide or protein by covalent bonding, a process which takes place in or near the rough endoplasmic reticulum.[1]
Golgi apparatus


Hayflick limit
The study or analysis of the microscopic anatomy of biological tissues or of cells within tissues, particularly by making use of specialized techniques to distinguish structures and functions based on visual morphology and differential staining. In practice the term is sometimes used more broadly to include cytology.
See cytosol.


Between two or more cells. Contrast intracellular; see also extracellular.

Also interphase II.

The abbreviated pause in activities related to cell division that occurs during meiosis in some species, between the first and second meiotic divisions (i.e. meiosis I and meiosis II). DNA replication does not occur during interkinesis, unlike during the normal interphase that precedes meiosis I and mitosis.[3]
All stages of the cell cycle excluding cell division. A typical cell spends most of its life in interphase, during which it conducts everyday metabolic activities as well as the complete replication of its genome in preparation for mitosis or meiosis.
Within a cell or cells; i.e. inside the plasma membrane. Contrast intercellular and extracellular.
The infolding of a membrane toward the interior of a cell or organelle, or of a sheet of cells toward the interior of a developing embryo, tissue, or organ, forming a distinct membrane-lined pocket. In the case of individual cells, the invaginated pocket may proceed to separate from the source membrane entirely, creating a membrane-bound vesicle within the cell, as in endocytosis.[1]
Any chemical compound or macromolecule that facilitates the movement of ions across biological membranes, or more specifically, any chemical species that reversibly binds electrically charged atoms or molecules. Many ionophores are lipid-soluble proteins that catalyze the transport of monovalent and divalent cations across the hydrophobic lipid bilayers surrounding cells and vesicles.[1]



See nucleus.
ketogenic amino acid
Any movement or change in activity by a cell or a population of cells in response to a stimulus, such that the rate of the movement or activity is dependent on the intensity of the stimulus but not on the direction from which the stimulus occurs. Kinesis is often defined as any non-specific, non-directional response, in contrast to taxis and tropism.
A disc-shaped protein complex which assembles around the centromere of a chromosome during prometaphase of mitosis and meiosis, where it functions as the attachment point for microtubules of the spindle apparatus.
Krebs cycle
See citric acid cycle.



Also leptotene stage.

In meiosis, the first of five substages of prophase I, following interphase and preceding zygonema. During leptonema, the replicated chromosomes condense from diffuse chromatin into long, thin strands that are much more visible within the nucleus.
The disruption and decomposition of the plasma membrane surrounding a cell, or more generally of any membrane-bound organelle or vesicle, especially by osmotic, enzymatic, or other chemical or mechanical processes which compromise the membrane's integrity and thereby cause the unobstructed interchange of the contents of intracellular and extracellular spaces. Lysis generally implies the complete and irreversible loss of intracellular organization as a result of the release of the cell's internal components and the dilution of the cytosol, and therefore the death of the cell. Such a cell is said to be lysed, and a fluid containing the contents of lysed cells (often including nucleic acids, proteins, and many other organic molecules) is called a lysate. Lysis may occur both naturally and artificially, and is a normal part of the cellular life cycle.


M phase
See mitosis.
A specialized type of cell division which occurs exclusively in sexually reproducing eukaryotes, during which DNA replication is followed by two consecutive rounds of cell division to ultimately produce four genetically unique daughter cells, each with half the number of chromosomes as the original parent cell. Meiosis only occurs in cells of the sex organs, and serves the purpose of generating haploid gametes such as sperm, eggs, or spores, which are later fused during fertilization. The two meiotic divisions, known as Meiosis I and Meiosis II, may also include various genetic recombination events between homologous chromosomes.
meiotic spindle
See spindle apparatus.
The stage of mitosis and meiosis that occurs after prometaphase and before anaphase, during which the centromeres of the replicated chromosomes align along the equator of the cell, with each kinetochore attached to the mitotic spindle.
The smaller of the two types of nuclei that occur in pairs in the cells of some ciliated protozoa. Whereas the larger macronucleus is polyploid, the micronucleus is diploid and generally transcriptionally inactive.[1]
See filopodium.

(pl.) microtrabeculae

A fine protein filament of the cytoskeleton. Multiple filaments form the microtrabecular network.[1]
microtubule-organizing center
mid body
The centrally constricted region that forms across the central axis of a cell during cell division, constricted by the closing of the contractile ring until the daughter cells are finally separated.[1]
middle lamella
In eukaryotic cells, the part of the cell cycle during which the division of the nucleus takes place and replicated chromosomes are separated into two distinct nuclei. Mitosis is generally preceded by the S phase of interphase, when the cell's DNA is replicated, and either occurs simultaneously with or is followed by cytokinesis, when the cytoplasm and plasma membrane are divided into two new daughter cells. Colloquially, the term "mitosis" is often used to refer to the entire process of cell division, not just that of the nucleus.
mitotic index (MI)
The proportion of cells within a sample which are undergoing mitosis at the time of observation, typically expressed as a percentage or as a value between 0 and 1. The number of cells dividing by mitosis at any given time can vary widely depending on organism, tissue, developmental stage, and culture media, among many other factors.[1]
mitotic spindle
See spindle apparatus.
monoclonal antibody (mAb)
motor protein


nicotinamide adenine dinucleotide (NAD)
nicotinamide adenine dinucleotide phosphate (NADP+, NADP)
nuclear cage
nuclear envelope
A sub-cellular barrier consisting of two lipid bilayer membranes that surrounds the nucleus in eukaryotic cells.
nuclear pore
nuclear transfer
Any of a diverse class of enzymes capable of cleaving the phosphodiester bonds connecting adjacent nucleotides in a nucleic acid molecule (the opposite of a ligase). Nucleases may cleave randomly or at specific recognition sequences. They are ubiquitous and imperative for normal cellular function, and are also widely employed in molecular biology techniques.
nucleic acid
A long, polymeric macromolecule made up of smaller monomers called nucleotides which are chemically linked to one another in a chain. Two specific types of nucleic acid, DNA and RNA, are common to all living organisms, serving to encode the genetic information governing the construction, development, and ordinary processes of all biological systems. This information, contained within the order or sequence of the nucleotides, is translated into proteins, which direct all of the chemical reactions necessary for life.

Also prokaryon.

An irregularly shaped region within a prokaryotic cell which contains most or all of the cell's genetic material, but is not enclosed by a nuclear membrane as in eukaryotes.
An organic molecule composed of a nitrogenous base bonded to a five-carbon sugar (either ribose or deoxyribose). A nucleotide additionally includes one or more phosphate groups.

Also nucleoside monophosphate (NMP).

An organic molecule that serves as the monomer or subunit of nucleic acid polymers, including RNA and DNA. Each nucleotide is composed of three connected functional groups: a nitrogenous base, a five-carbon sugar (either ribose or deoxyribose), and a single phosphate group. Though technically distinct, the term "nucleotide" is often used interchangeably with nitrogenous base, nucleobase, and base pair when referring to the sequences that make up nucleic acids. A nucleotide lacking a phosphate group is called a nucleoside.

(pl.) nuclei

A large spherical or lobular organelle surrounded by a nuclear membrane which functions as the main storage compartment for the genetic material of eukaryotic cells, including the DNA comprising chromosomes, as well as the site of RNA synthesis during transcription. The vast majority of eukaryotic cells have a single nucleus, though some cells may have more than one nucleus, either temporarily or permanently, and in some organisms there exist certain cell types (e.g. mammalian erythrocytes) which lose their nuclei upon reaching maturity, effectively becoming anucleate. The nucleus is exclusive to eukaryotes; the cells of prokaryotes such as bacteria lack nuclei entirely.[1]


occluding junction
oxidative phosphorylation


perinuclear space
The space between the inner and outer phospholipid layers of the nuclear envelope.
A type of cell which functions as part of the immune system by engulfing and ingesting harmful foreign molecules, bacteria, and dead or dying cells, in a process known as phagocytosis.
phospholipid bilayer
plasma membrane
The number of complete sets of chromosomes in a cell, and hence the number of possible alleles present within the cell at any given autosomal locus.
A long, continuous, and unbranched polymeric chain of amino acid monomers linked by covalent peptide bonds, typically longer than a peptide. Proteins generally consist of one or more polypeptides arranged in a biologically functional way.
(of a cell or organism) Having more than two homologous copies of each chromosome; i.e. any ploidy level that is greater than diploid. Polyploidy may occur as a normal condition of chromosomes in certain cells or even entire organisms, or it may result from errors in cell division or mutations causing the duplication of the entire chromosome set.
The second stage of cell division in mitosis, following prophase and preceding metaphase, during which the nuclear membrane disintegrates, the chromosomes inside form kinetochores around their centromeres, microtubules emerging from the poles of the mitotic spindle reach the nuclear space and attach to the kinetochores, and motor proteins associated with the microtubules begin to push the chromosomes toward the center of the cell.
The first stage of cell division in both mitosis and meiosis, occurring after interphase and before prometaphase, during which the DNA of the chromosomes is condensed into chromatin, the nucleolus disintegrates, centrosomes move to opposite ends of the cell, and the mitotic spindle forms.
A polymeric macromolecule composed of one or more long chains of amino acids linked by peptide bonds. Proteins are the three-dimensional structures created when these chains fold into specific higher-order arrangements following translation, and it is this folded structure which determines a protein's chemical activity and hence its biological function. Ubiquitous and fundamental in all living organisms, proteins are the primary means by which the functions of life are performed, participating in the vast majority of the biochemical reactions that occur inside and outside of cells.
proton motive force
pyruvic acid





S phase
somatic cell
spindle apparatus
stem cell
1.  A chemical compound or molecule upon which a particular enzyme directly acts, often but not necessarily binding the molecule by forming one or more chemical bonds.[1] See also ligand.
2.  The substance, biotic or abiotic, upon which an organism grows or lives, or by which it is supported; e.g. a particular growth medium used in cell culture.
Any of a class of transmembrane transporter proteins which facilitate the transport of two or more different molecules across the membrane at the same time and in the same direction; e.g. glucose and sodium ions. Contrast antiporter and uniporter.


The final stage of cell division in both mitosis and meiosis, occurring after anaphase and before or simultaneously with cytokinesis, during which a nuclear membrane is synthesized around each set of chromatids, nucleoli are reassembled, and the mitotic spindle is disassembled. Following cytokinesis, the new daughter cells resume interphase.
transmembrane protein
tricarboxylic acid cycle (TCA)
See citric acid cycle.






Warburg effect




See also


  1. ^ a b c d e f g h i j k l m n o p MacLean, Norman (1987). Dictionary of Genetics & Cell Biology. New York: New York University Press. ISBN 0-8147-5438-4.
  2. ^ Nishikawa, S. (2007). "Reprogramming by the numbers". Nature Biotechnology. 25 (8): 877–878. doi:10.1038/nbt0807-877. PMID 17687365. S2CID 39773318.
  3. ^ a b c King, Robert C.; Stansfield, William D.; Mulligan, Pamela K. (2006). A Dictionary of Genetics (7th ed.). Oxford: Oxford University Press. ISBN 978-0-19-530762-7.