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

Glossary G:21
multipass transmembrane protein Membrane protein in
which the polypeptide chain crosses the lipid bilayer more than
once. (Figure 10–17)
multivesicular bodies Intermediates in the endosome
maturation process; early endosomes that are on their way to
becoming late endosomes.
mutation Heritable change in the nucleotide sequence of a
chromosome. (Panel 8–2, pp. 486–487)
mutation rate The rate at which changes (mutations) occur in
DNA sequences.
mutualism Ecological relationship between microbes and
their host in which both the microbe and host benefit.
Myc Transcription regulatory protein that is activated when a
cell is stimulated to grow and divide by extracellular signals. It
activates the transcription of many genes, including those that
stimulate cell growth. (Figure 17–61)
myelin sheath Insulating layer of specialized cell
membrane wrapped around vertebrate axons. Produced
by oligodendrocytes in the central nervous system and by
Schwann cells in the peripheral nervous system. (Figure 11–33)
myeloid cell Any white blood cell other than a lymphocyte.
(Figure 22–31)
myoblast Mononucleated, undifferentiated muscle precursor
cell. A skeletal muscle cell is formed by the fusion of multiple
myoblasts. (Figure 22–19)
myofibril Long, highly organized bundle of actin, myosin, and
other proteins in the cytoplasm of muscle cells that contracts
by a sliding filament mechanism.
myosin Type of motor protein that uses the energy of ATP
hydrolysis to move along actin filaments.
Na + -K + pump (Na + -K + ATPase) Transmembrane carrier
protein found in the plasma membrane of most animal cells that
pumps Na + out of and K + into the cell, using energy derived
from ATP hydrolysis. (Figure 11–15)
NAD + /NADH (nicotinamide adenine dinucleotide/reduced
nicotinamide adenine dinucleotide) Electron carrier system
that participates in oxidation–reduction reactions, such as the
oxidation of food molecules. NAD + accepts the equivalent of
a hydride ion (H – , a proton plus two electrons) to become the
activated carrier NADH. The NADH formed donates its highenergy
electrons to the ATP-generating process of oxidative
phosphorylation. (Figure 2–36)
NADH dehydrogenase complex First of the three electrondriven
proton pumps in the mitochondrial respiratory chain,
also known as Complex I. It accepts electrons from NADH and
passes them to a quinone. (Figure 14–18)
NADP + /NADPH (nicotinamide adenine dinucleotide
phosphate/reduced nicotinamide adenine dinucleotide
phosphate) Electron carrier system closely related to NAD + /
NADH, but used almost exclusively in reductive biosynthetic,
rather than catabolic, pathways. (Figure 2–36)
naïve cell In immunology: a T or B lymphocyte that
proliferates and differentiates into an effector cell or memory cell
when it encounters its specific foreign antigen for the first time.
(Figure 24–17)
natural killer cell (NK cell) Cytotoxic cell of the innate
immune system that can kill virus-infected cells and some
cancer cells.
natural regulatory T cell A regulatory T cell (T reg cell) that
develops in the thymus and helps maintain self-tolerance.
negative selection Process by which thymocytes expressing
a T cell receptor with high affinity for a self peptide bound to a
self-MHC protein are eliminated by undergoing apoptosis.
negative staining A technique in electron microscopy
enabling fine detail of isolated macromolecules to be seen.
Samples are prepared such that a very thin film of heavy-metal
salt covers everywhere except where excluded by the presence
of macromolecules, which allow electrons to pass through,
creating a reverse or negative image of the molecule.
Nernst equation Equation that computes relates the
electrical potential (voltage) generated by differences in ion
concentrations across a membrane.
Netrin Signal protein, secreted by cells of the neural tube floor
plate, responsible for attracting growth cones of commissural
axons toward and across the midline.
neural crest Collection of cells located along the line where
the neural tube pinches off from the surrounding epidermis in
the vertebrate embryo. Neural crest cells migrate to give rise to
a variety of tissues, including neurons and glia of the peripheral
nervous system, pigment cells of the skin, and the bones of the
face and jaws. (Figure 19–8)
neural map Regular mapping of neurons of a similar type
from one territory to another, such that there are orderly
projections of one array of neurons onto another.
neural tube Tube of ectoderm that will form the brain and
spinal cord in a vertebrate embryo. (Figure 21–56)
neurofilament Type of intermediate filament found in nerve
cells. (Figure 16–72)
neuromuscular junction Specialized chemical synapse
between an axon terminal of a motor neuron and a skeletal
muscle cell. (Figure 11–37)
neuron (nerve cell) Impulse-conducting cell of the nervous
system, with extensive processes specialized to receive,
conduct, and transmit signals. (Figures 11–28 and 21–66)
neuronal specificity Nonequivalence among neurons; an
intrinsic characteristic that guides axons to their appropriate
target sites.
neurotransmitter Small signal molecule secreted by the
presynaptic nerve cell at a chemical synapse to relay the
signal to the postsynaptic cell. Examples include acetylcholine,
glutamate, GABA, glycine, and many neuropeptides.
neurotrophic factor Factor released in limited amounts by a
target tissue that the neurons innervating that tissue require to
survive.
neurotrophin Family of signal proteins that promote the
survival and growth of specific classes of neurons.
neutrophil White blood cell that is specialized for the uptake
of particulate material by phagocytosis. Enters tissues that
become infected or inflamed. (Figure 24–5)
NFκB protein Latent transcription regulator that is activated
by various intracellular signaling pathways when cells are
stimulated during immune, inflammatory, or stress responses.
Also has important roles in animal development. (Figure 15–62)
nitric oxide (NO) Gaseous signal molecule that is widely used
in cell–cell communication in both animals and plants.
(Figure 15–40)
nitrogen fixation Biochemical process carried out by certain
bacteria that reduces atmospheric nitrogen (N 2 ) to ammonia,
leading eventually to various nitrogen-containing metabolites.