Essential Cell Biology 5th edition

Glossary G:13
oxidative phosphorylation
Membrane-based process in bacteria and mitochondria in
which ATP formation is driven by the transfer of electrons
from food molecules to molecular oxygen.
p53
Transcription regulator that controls the cell’s response to
DNA damage, preventing the cell from entering S phase
until the damage has been repaired or inducing the cell to
commit suicide if the damage is too extensive; mutations in
the gene encoding this protein are found in many human
cancers.
pairing
In meiosis, the process by which a pair of duplicated
homologous chromosomes attach to one another to form a
structure containing four sister chromatids.
passive transport
The spontaneous movement of a solute down its
concentration gradient across a cell membrane via a
membrane transport protein, such as a channel or a
transporter.
patch-clamp recording
Technique used to monitor the activity of ion channels in a
membrane; involves the formation of a tight seal between
the tip of a glass electrode and a small region of cell
membrane, and manipulation of the membrane potential
by varying the concentrations of ions in the electrode.
pedigree
Chart showing the line of descent, or ancestry, of an
individual organism.
peptide bond
Covalent chemical bond between the
carbonyl group of one amino acid and the
amino group of a second amino acid. (See
Panel 2–6, pp. 76–77.)
peroxisome
Small membrane-enclosed organelle that contains enzymes
that degrade lipids and destroy toxins.
pH scale
Concentration of hydrogen ions in a solution, expressed
as a logarithm. An acidic solution with pH 3 will contain
10 –3 M hydrogen ions.
phagocytic cell
A cell such as a macrophage or neutrophil that is specialized
to take up particles and microorganisms by phagocytosis.
phagocytosis
The process by which particulate material is engulfed
(“eaten”) by a cell. Prominent in predatory cells, such as
Amoeba proteus, and in cells of the vertebrate immune
system, such as macrophages.
phenotype
The observable characteristics of a cell or organism.
phosphatidylcholine
Common phospholipid present in abundance in most cell
membranes; uses choline attached to a phosphate as its
head group.
phosphoinositide 3-kinase (PI 3-kinase)
Enzyme that phosphorylates inositol phospholipids in
the plasma membrane, which generates docking sites for
intracellular signaling proteins that promote cell growth
and survival.
phospholipase C
Enzyme associated with the plasma membrane that
generates two small messenger molecules in response to
activation.
O
C
N
H
phospholipid
A major type of lipid molecule in many cell
membranes. Generally composed of two fatty
acid tails linked to one of a variety of phosphatecontaining
polar groups.
photosynthesis
The process by which plants, algae, and some bacteria
use the energy of sunlight to drive the synthesis of organic
molecules from carbon dioxide and water.
photosystem
Large multiprotein complex containing chlorophyll that
captures light energy and converts it into chemical-bond
energy; consists of a set of antenna complexes and a
reaction center.
phragmoplast
In a dividing plant cell, structure made of microtubules and
membrane vesicles that guides the formation of a new cell
wall.
phylogenetic tree
Diagram or “family tree” showing the evolutionary
relationships among groups of organisms or proteins.
pinocytosis
Type of endocytosis in which soluble materials are taken
up from the environment and incorporated into vesicles for
digestion. (Literally, “cell drinking.”)
plasma membrane
The protein-containing lipid bilayer that surrounds a living
cell.
plasmid
Small, circular DNA molecule that replicates independently
of the genome. Used extensively as a vector for DNA
cloning.
plasmodesma (plural plasmodesmata)
Cell–cell junction that connects one plant cell to the next;
consists of a channel of cytoplasm lined by membrane.
pluripotent
Capable of giving rise to any type of cell or tissue.
point mutation
Change in a single nucleotide pair in a DNA sequence.
polar
In chemistry, describes a molecule or bond in which
electrons are distributed unevenly.
polarity
An inherent asymmetry that allows one end of an object
to be distinguished from another; can refer to a molecule,
a polymer (such as an actin filament), or even a cell (for
example, an epithelial cell that lines the mammalian small
intestine).
polyadenylation
The addition of multiple adenine nucleotides to the 3′ end of
a newly synthesized mRNA molecule.
polymer
Long molecule made by covalently linking multiple identical
or similar subunits (monomers).
polymerase chain reaction (PCR)
Technique for amplifying selected regions of DNA by
multiple cycles of DNA synthesis; can produce billions of
copies of a given sequence in a matter of hours.
polymorphism
DNA sequence for which two or more variants are present
at high frequency in the general population.
polypeptide backbone
Repeating sequence of the atoms (–N–C–C–) that form the