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:23
specific G protein (Golf) and resultant increases in cAMP open
cyclic-AMP-gated cation channels, allowing Na + influx and
depolarization and initiation of a nerve impulse.
oligodendrocyte Glial cell in the vertebrate central nervous
system that forms a myelin sheath around axons. Compare
Schwann cell.
oncogene An altered gene whose product can act in a
dominant fashion to help make a cell cancerous. Typically, an
oncogene is a mutant form of a normal gene (proto-oncogene)
involved in the control of cell growth or division. (Figure 20–17)
open reading frame (ORF) A continuous nucleotide
sequence free from stop codons in at least one of the three
reading frames (and thus with the potential to code for protein).
opportunistic pathogens Microbes of the normal flora that
can cause disease only if the immune systems are weakened or
if they gain access to a normally sterile part of the body.
optogenetics Use of genetically engineered
channelrhodopsin and other light-responsive ion channels
and transporters to modulate neuron function and hence
analyze the neurons and circuits underlying complex functions,
including behaviors in whole animals. (Figure 11–32)
organelle Subcellular compartment or large macromolecular
complex, often membrane-enclosed, that has a distinct
structure, composition, and function. Examples are nucleus,
nucleolus, mitochondrion, Golgi apparatus, and centrosomes.
(Figure 1–25)
Organizer Specialized tissue at the dorsal lip of the
blastopore in an amphibian embryo; a source of signals that
help to orchestrate formation of the embryonic body axis.
origin recognition complex (ORC) Large protein complex
that is bound to the DNA at origins of replication in eukaryotic
chromosomes throughout the cell cycle. (Figure 5–31)
orthologs Genes or proteins from different species that are
similar in sequence because they are descendants of the same
gene in the last common ancestor of those species. Compare
paralogs. (Figure 1–21)
osteoblast Cell that secretes matrix of bone. (Figure 22–14)
osteoclast Macrophage-like cell that erodes bone, enabling
it to be remodeled during growth and in response to stresses
throughout life. (Figure 22–16)
osteocyte Nondividing cell in bone that develops from an
osteoblast and is embedded in bone matrix. (Figure 22–14)
outer membrane Mitochondrial membrane that is in contact
with the cytosol.
outer mitochondrial membrane Membrane that separates
the organelle from the cytosol.
outer nuclear membrane One of two concentric
membranes comprising the nuclear envelope; surrounds the
inner nuclear membrane and is continuous with the inner
nuclear membrane and the membrane of the endoplasmic
reticulum.
OXA complex Protein translocator in the inner mitochondrial
membrane that mediates insertion of inner membrane proteins.
oxidation (verb oxidize) Loss of electrons from an atom, as
occurs during the addition of oxygen to a molecule or when a
hydrogen is removed. Opposite of reduction. (Figure 2–20)
oxidative phosphorylation Process in bacteria and
mitochondria in which ATP formation is driven by the transfer
of electrons through the electron transport chain to molecular
oxygen. Involves the intermediate generation of a proton
gradient (pH gradient) across a membrane and a chemiosmotic
coupling of that gradient to the ATP synthase. (Figures 14–12)
oxidative phosphorylation Process in bacteria and
mitochondria in which ATP formation is driven by the
transfer of electrons through the electron-transport chain to
molecular oxygen. Involves the intermediate generation of an
electrochemical proton gradient across a membrane and a
chemiosmotic coupling of that gradient to the ATP synthase.
(Figure 14–10)
P-type pumps A class of ATP-driven pumps comprising
structurally and functionally related multipass transmembrane
proteins that phosphorylate themselves during the pumping
cycle. The class includes many of the ion pumps responsible
for setting up and maintaining gradients of Na + , K + , H + , and
Ca 2+ across cell membranes. (Figure 11–12)
p53 A transcription regulatory protein that is activated by
damage to DNA and is involved in blocking further progression
through the cell cycle. (Figures 20–37 and 20–40)
p53 Tumor suppressor gene that is mutated in about half
of human cancers. Encodes a transcription regulator that is
activated by damage to DNA and is involved in blocking further
progression through the cell cycle. (Figure 20–27)
pair-rule gene In Drosophila development, a gene expressed
in a series of regular transverse stripes along the body of the
embryo and which helps to determine its segments.
(Figure 21–19)
pairing In meiosis, the lining up of the two homologous
chromosomes along their length. (Figure 17–54)
papillomaviruses Class of viruses responsible for human
warts and a prime example of DNA tumor viruses, being a
cause of cancer of the uterine cervix.
paracrine signaling Short-range cell–cell communication
via secreted signal molecules that act on neighboring cells.
(Figure 15–2)
paralogs Genes or proteins that are similar in sequence
because they are the result of a gene duplication event
occurring in an ancestral organism. Those in two different
organisms are less likely to have the same function than are
orthologs. Compare orthologs. (Figure 1–21)
parasitism Ecological relationship between microbes and
their host in which the microbe benefits to the detriment of the
host, as is often the case for pathogens.
passengers Mutations that have occurred in the same cell as
driver mutations, but which are irrelevant to the development of
the cancer.
passive transport (facilitated diffusion) Transport of a
solute across a membrane down its concentration gradient or
its electrochemical gradient, using only the energy stored in the
gradient. (Figure 11–4)
patch-clamp recording Electrophysiological technique
in which a tiny electrode tip is sealed onto a patch of cell
membrane, thereby making it possible to record the flow of
current through individual ion channels in the patch.
(Figure 11–34)
Patched Transmembrane protein predicted to cross the
plasma membrane 12 times; much is in intracellular vesicles
and some is on the cell surface where it binds the Hedgehog
protein.