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:17
inner nuclear membrane One of two concentric membranes
comprising the nuclear envelope; contnuous with the outer
nuclear membrane; contains specific proteins as anchoring
sites for chromatin and the nuclear lamina.
inositol 1,4,5-trisphosphate (IP 3 ) Small intracellular signaling
molecule produced during activation of the inositol phospholipid
signaling pathway. Acts to release Ca 2+ from the endoplasmic
reticulum. (Figures 15–28 and 15–29)
inositol phospholipid signaling pathway Intracellular
signaling pathway that starts with the activation of
phospholipase C and the generation of IP 3 and diacylglycerol
(DAG) from inositol phospholipids in the plasma membrane.
The DAG helps to activate protein kinase C. (Figures 15–28 and
15–29)
integrin Transmembrane adhesion protein that is involved in
the attachment of cells to the extracellular matrix and to each
other. (Figure 19–3 and Table 19–1, p. 1037)
interaction domain Compact protein module, found in
many intracellular signaling proteins, that binds to a particular
structural motif (e.g., a short peptide sequence, a covalent
modification, or another protein domain) in another protein or
lipid.
interferon-α (IFNα) and interferon-β (IFNβ) Cytokines
(type I interferons) produced by mammalian cells as a general
response to a viral infection.
intermembrane space Compartment of mitochondrion
between by the outer and inner mitochondrial membranes.
internal ribosome entry site (IRES) Specific site in a
eukaryotic mRNA, other than at the 5′ end, at which translation
can be initiated. (Figure 7–68)
interphase Long period of the cell cycle between one mitosis
and the next. Includes G 1 phase, S phase, and G 2 phase.
(Figure 17–4)
interpolar microtubule In the mitotic or meiotic spindle, a
microtubule interdigitating at the equator with the microtubules
emanating from the other pole. (Figure 17–23)
intracellular pathogens Pathogens, including all viruses and
many bacteria and protozoa, that enter and replicate inside
host cells to cause disease.
intrinsic pathway (mitochondrial pathway) Pathway of
apoptosis activated from inside the cell in response to stress or
developmental signals; depends on the release into the cytosol
of mitochondrial proteins normally resident in the mitochondrial
intermembrane space.
intron Noncoding region of a eukaryotic gene that is
transcribed into an RNA molecule but is then excised by RNA
splicing during production of the mRNA or other functional
RNA. (Figure 4–15)
invadopodia Actin-rich protrusions extending in threedimensions
that are important for cells to cross tissue barriers
by degrading the extracellular matrix.
ion channel Transmembrane protein complex that forms
a water-filled channel across the lipid bilayer through which
specific inorganic ions can diffuse down their electrochemical
gradients. (Figure 11–22)
ion-channel-coupled receptor (transmitter-gated ion
channel, ionotropic receptor) Ion channel found at
chemical synapses in the postsynaptic plasma membranes of
nerve and muscle cells. Opens only in response to the binding
of a specific extracellular neurotransmitter. The resulting inflow
of ions leads to the generation of a local electrical signal in the
postsynaptic cell. (Figures 15–6 and 11–35)
ion-sensitive indicators Molecules whose light emission
reflects the local concentration of a particular ion; some are
luminescent (emitting light spontaneously) while others are
fluorescent (emitting light on exposure to light).
IP 3 -gated Ca 2+ -release channel (IP 3 receptor) Gated Ca 2+
channel in the ER membrane that opens on binding cytosolic
IP 3 , releasing stored Ca 2+ into the cytosol. (Figure 15–29)
iron–sulfur cluster Electron-transporting group consisting
of either two or four iron atoms bound to an equal number of
sulfur atoms, found in a class of electron-transport proteins.
(Figure 14–16)
J gene segment Short DNA sequences that encodes part
of the variable region of light and heavy immunoglobulin chains
and of α and β chains of T cell receptors. (Figures 24–28 and
24–29)
JAK–STAT signaling pathway Signaling pathway activated
by cytokines and some hormones, providing a rapid route
from the plasma membrane to the nucleus to alter gene
transcription. Involves cytoplasmic Janus kinases (JAKs), and
signal transducers and activators of transcription (STATs).
Janus kinases (JAKs) Cytoplasmic tyrosine kinases
associated with cytokine receptors, which phosphorylate and
activate transcription regulators called STATs.
junctional diversification The random loss and gain of
nucleotides at joining sites during V(D)J recombination that
occurs during B and T cell development when the cells are
assembling the gene segments that encode their antigen
receptors. It enormously increases the diversity of V-region
coding sequences.
K + leak channel K + -transporting ion channel in the plasma
membrane of animal cells that remains open even in a “resting”
cell.
karyotype Display of the full set of chromosomes of a cell,
arranged with respect to size, shape, and number.
keratin Type of intermediate filament, commonly produced by
epithelial cells.
kinase cascade Intracellular signaling pathway in which one
protein kinase, activated by phosphorylation, phosphorylates
the next protein kinase in the sequence, and so on, relaying the
signal onward.
kinesin Member of one of the two main classes of motor
proteins that use the energy of ATP hydrolysis to move along
microtubules. (Figure 16–56)
kinesin-1 Motor protein associated with microtubules that
transports cargo within the cell; also called “conventional
kinesin.”
kinetic proofreading A principle for increasing the specificity
of catalysis. In the synthesis of DNA, RNA, and proteins, it
refers to a time delay that begins with an irreversible step (such
as ATP or GTP hydrolysis) and during which incorrect base
pairs are more likely to dissociate than correct pairs.
kinetochore Large protein complex that connects the
centromere of a chromosome to microtubules of the mitotic
spindle. (FIgure 17–30)
kinetochore microtubule In the mitotic or meiotic spindle, a
microtubule that connects the spindle pole to the kinetochore
of a chromosome.