F&G: TERMS IN MOLECULAR BIOLOGY CELL

facultative pathogens

Bacteria that replicate in an environmental reservoir such as water or soil and only cause disease if they happen to encounter a susceptible host.

FAD/FADH2 (flavin adenine dinucleotide/reduced flavin
adenine dinucleotide)

Electron carrier system that functions in the citric acid cycle and fatty acid oxidation. One molecule of FAD gains two electrons plus two protons in becoming the activated carrier FADH2.

Fas (Fas protein, Fas death receptor)

Transmembrane death receptor that initiates apoptosis when it binds its extracellular ligand (Fas ligand).

Fas ligand

Ligand that activates the cell-surface death receptor, Fas, triggering the extrinsic pathway of apoptosis.

fat

Energy-storage lipid in cells. Composed of triglycerides—
fatty acids esterified with glycerol.

fate map

Representation showing which cell types will later derive from which regions of a tissue; e.g. from the blastula.

Fc receptor

One of a family of cell-surface receptors that bind the tail region (Fc region) of an antibody molecule.

feedback inhibition

The process in which a product of a reaction feeds back to inhibit a previous reaction in the same pathway.

fermentation

Anaerobic energy-yielding metabolic pathway involving the oxidation of organic molecules.

fibril-associated collagen

Mediates the interactions of collagen fibrils with one another and with other matrix macromolecules to help determine the organization of the fibrils in the matrix.

fibrillar collagen

Class of fibril-forming collagens (including type I collagen, the most common type and the principal collagen of skin and bone) that have long ropelike structures with few or no interruptions and which assemble into collagen fibrils.

fibroblast

Common cell type found in connective tissue. Secretes an extracellular matrix rich in collagen and other extracellular matrix macromolecules.

fibronectin

Extracellular matrix protein involved in adhesion of cells to the matrix and guidance of migrating cells during embryogenesis.

filopodium (plural filopodia) (microspike)

Thin, spike-like protrusion with an actin filament core, generated on the leading edge of a crawling animal cell.

firing rule

Important principle governing synapse reinforcement and elimination during development of the nervous system: when two (or more) neurons synapsing on the same target cell fire at the same time, they reinforce their connections to that cell; when they fire at different times, they compete, so that all but one of them tend to be eliminated.

flagellum

(plural flagella) Long, whiplike protrusion whose undulations drive a cell through a fluid medium. Eukaryotic
flagella are longer versions of cilia.

fluorescence microscope

Microscope designed to view material stained with fluorescent dyes or proteins.

fluorescence recovery after photobleaching (FRAP)

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.

fluorescence resonance energy transfer (FRET)

Technique for monitoring the closeness of two fluorescently
labeled molecules (and thus their interaction) in cells.

focal adhesion kinase (FAK)

Cytoplasmic tyrosine kinase present at cell–matrix junctions (focal adhesions) in association with the cytoplasmic tails of integrins.

follicular helper T cell (TFH)

Type of T cell located in lymphoid follicles that secretes various cytokines to stimulate B cells to undergo antibody class switching and somatic hypermutation.

formin

Dimeric protein that nucleates the growth of straight, unbranched actin filaments that can be cross-linked by other
proteins to form parallel bundles.

free energy (G) (Gibbs free energy)

The energy that can be extracted from a system to drive reactions. Takes into account changes in both energy and entropy.

free ribosome

Ribosome that is free in the cytosol, unattached to any membrane.

Frizzled

Family of cell-surface receptors that are seven-pass
transmembrane proteins that resemble GPCRs in structure
but do not generally work through the activation of G proteins.

fungus

(plural fungi) Kingdom of eukaryotic organisms that
includes the yeasts, molds, and mushrooms. Many plant
diseases and a relatively small number of animal diseases are caused by fungi.

fusion protein

Engineered protein that combines two or more normally separate polypeptides. Produced from a recombinant gene.

G1 phase

Gap 1 phase of the eukaryotic cell-division cycle, between the end of mitosis and the start of DNA synthesis.

ganglioside

Any glycolipid having one or more sialic acid residues in its structure. Found in the plasma membrane of eukaryotic cells and especially abundant in nerve cells.

gap gene

In Drosophila development, a gene that is expressed in specific broad regions along the anteroposterior axis of the early embryo, and which helps designate the main divisions of the insect body.

gap junction

Communicating channel-forming cell–cell junction present in most animal tissues that allows ions and small molecules to pass from the cytoplasm of one cell to the cytoplasm of the next.

gastrulation

Important stage in animal embryogenesis during which the embryo is transformed from a ball of cells to a structure with a gut (a gastrula).

gated transport

Movement of proteins between the cytosol and the nucleus through nuclear pore complexes in the nuclear envelope that function as selective gates.

geminin

Protein that prevents the formation of new prereplicative complexes during S phase and mitosis, thus ensuring that the chromosomes are replicated only once in each cell cycle.

gene

Region of DNA that is transcribed as a single unit and carries information for a discrete hereditary characteristic,
usually corresponding to (1) a single protein (or set of related proteins generated by variant post-transcriptional processing), or (2) a single RNA (or set of closely related RNAs).

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.

gene conversion

Process by which DNA sequence information can be transferred from one DNA helix (which remains unchanged) to another DNA helix whose sequence is altered.

gene family

The set of genes in an organism related in DNA sequence due to their derivation from the same ancestor.

gene segments

In immunology: short DNA sequences that are joined together during B cell and T cell development to produce the coding sequences for immunoglobulins and T cell receptors, respectively.

general transcription factor

Any of the proteins whose assembly at all promoters of a given type is required for the binding and activation of RNA polymerase and the initiation of transcription.

genetic code

The set of rules specifying the correspondence between nucleotide triplets (codons) in DNA or RNA and amino
acids in proteins.

genetic instability

Abnormally increased spontaneous mutation rate, such as occurs in cancer cells.

genetic screen

Procedure for discovery of genes affecting a specific phenotype by surveying large numbers of mutagenized
individuals.

genetics

The study of the genes of an organism on the basis of heredity and variation.

genome

The totality of genetic information belonging to a cell or an organism; in particular, the DNA that carries this information.

genome annotation

Process attempting to mark out all
the genes (protein-coding and noncoding) in a genome and
ascribing functions to each.

genomic imprinting

Phenomenon in which a gene is either expressed or not expressed in the offspring depending on
which parent it is inherited from.

genomic library

Collection of cloned DNA molecules representing an entire genome.

genotype

Genetic constitution of an individual cell or organism.

germ cell

A cell in the germ line of an organism, which includes the haploid gametes and their specified diploid precursor cells.

germ layer

One of the three primary tissue layers (endoderm,mesoderm, and ectoderm) of an animal embryo.

glial cell

Supporting non-neural cell of the nervous system. Includes oligodendrocytes and astrocytes in the vertebrate central nervous system and Schwann cells in the peripheral
nervous system.

glycogen

Polysaccharide composed exclusively of glucose units. Used to store energy in animal cells.

glycolipid

Lipid molecule with a sugar residue or oligosaccharide attached.

glycolysis

Ubiquitous metabolic pathway in the cytosol in
which sugars are incompletely degraded with production of
ATP.

glycoprotein

Any protein with one or more saccharide or oligosaccharide chains covalently linked to amino acid side chains.

glycosaminoglycan (GAG)

Long, linear, highly charged polysaccharide composed of a repeating pair of sugars, one of which is always an amino sugar.

glycosylphosphatidylinositol anchor (GPI anchor)

Lipid linkage by which some membrane proteins are bound to the membrane.

Golgi apparatus (Golgi complex)

Complex organelle in eukaryotic cells, centered on a stack of flattened, membrane-enclosed spaces, in which proteins and lipids transferred from the endoplasmic reticulum are modified and sorted.

GPCR kinase (GRK)

Member of a family of enzymes that phosphorylates multiple serines and threonines on a GPCR to produce receptor desensitization.

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.

G-protein-coupled receptor (GPCR)

A seven-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.

Gram negative

Description for bacteria that do not stain with Gram stain as a result of having a thinner peptidoglycan cell wall outside their inner (plasma) membrane, and on an additional outer membrane.

Gram positive

Description for bacteria that stain positive with Gram stain due to a thick layer of peptidoglycan cell wall outside their inner (plasma) membrane.

Gram staining

A technique for classifying bacteria based on differences in the structure of the bacterial cell wall and outer surface.

granulocyte

Category of white blood cell distinguished by conspicuous cytoplasmic granules. Includes neutrophils, basophils, and eosinophils.

granulocyte/macrophage (GM) progenitor cell

Committed progenitor cell in the bone marrow that gives rise to neutrophils and macrophages.

green fluorescent protein (GFP)

Fluorescent protein isolated from a jellyfish. Widely used as a marker in cell biology.

growth cone

Migrating motile tip of a growing nerve cell axon or dendrite.

growth factor

Extracellular signal protein that can stimulate a cell to grow. They often have other functions as well, including stimulating cells to survive or proliferate.

growth hormone (GH)

Mammalian hormone secreted by the pituitary gland into the bloodstream that stimulates growth throughout the body.