Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

G:12 Glossary
exocytosis Excretion of material from the cell by vesicle
fusion with the plasma membrane; can occur constitutively or
be regulated.
exon 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 amino acids in
the protein. An exon is usually adjacent to a noncoding DNA
segment called an intron. (Figure 4–15)
exosome Large protein complex with an interior rich in
3′-to-5′ RNA exonucleases; degrades RNA molecules to
produce ribonucleotides.
extracellular pathogens Pathogens that disturb host cells
and can cause serious disease without replicating in host cells.
extracellular signal molecule Any secreted or cell-surface
chemical signal that binds to receptors and regulates the
activity of the cell expressing the receptor.
extrinsic pathway Pathway of apoptosis triggered by
extracellular signal proteins binding to cell-surface death
receptors.
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/FADH 2 (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 FADH 2 . (Figure 2–39)
Fas (Fas protein, Fas death receptor) Transmembrane
death receptor that initiates apoptosis when it binds its
extracellular ligand (Fas ligand). (Figure 18–5)
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.
(Figure 21–28)
Fc receptor One of a family of cell-surface receptors that
bind the tail region (Fc region) of an antibody molecule. Different
Fc receptors are specific for different classes of antibodies,
such as IgG, IgA, or IgE.
feedback inhibition The process in which a product of a
reaction feeds back to inhibit a previous reaction in the same
pathway. (Figures 3–55 and 3–56)
fermentation Anaerobic energy-yielding metabolic pathway
involving the oxidation of organic molecules. Anaerobic
glycolysis refers to the process whereby pyruvate is converted
into lactate or ethanol, with the conversion of NADH to NAD + .
(Figure 2–47)
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. This collagen (including types IX and XII) has a
flexible triple-stranded helical structure and binds to the surface
of the fibrils rather than forming aggregates.
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. Migrates and proliferates
readily in wounded tissue and in tissue culture.
fibronectin Extracellular matrix protein involved in adhesion
of cells to the matrix and guidance of migrating cells during
embryogenesis. Integrins on the cell surface are receptors for
fibronectin.
filopodium (plural filopodia) (microspike) Thin, spike-like
protrusion with an actin filament core, generated on the leading
edge of a crawling animal cell. (Figure 16–21)
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. Bacterial flagella are smaller
and completely different in construction and mechanism of
action. Compare cilium.
fluorescence microscope Microscope designed to view
material stained with fluorescent dyes or proteins. Similar to a
light microscope but the illuminating light is passed through one
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. (Figure 9–12)
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. (Figure 9–29)
fluorescence resonance energy transfer (FRET)
Technique for monitoring the closeness of two fluorescently
labeled molecules (and thus their interaction) in cells. Also
known as Förster resonance energy transfer. (Figure 9–26)
focal adhesion kinase (FAK) Cytoplasmic tyrosine kinase
present at cell–matrix junctions (focal adhesions) in association
with the cytoplasmic tails of integrins.
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 (T FH ) 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.
Förster resonance energy transfer see fluorescence
resonance energy transfer (FRET)
FRAP see fluorescence recovery after photobleaching
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. (Panel 2–7, pp. 102–103)
free ribosome Ribosome that is free in the cytosol,
unattached to any membrane.