Essential Cell Biology 5th edition

G:14 Glossary
core of a protein molecule and to which the amino acid side
chains are attached.
polypeptide, polypeptide chain
Linear polymer composed of multiple amino acids. Proteins
are composed of one or more long polypeptide chains.
positive feedback loop
An important form of regulation in
which the end product of a reaction
X
Y
or pathway stimulates continued
production or activity; controls a
+
variety of biological processes, including enzyme activity,
cell signaling, and gene expression.
post-transcriptional control
Regulation of gene expression that occurs after transcription
of the gene has begun; examples include RNA splicing and
translational control.
primary structure
The amino acid sequence of a protein.
primase
An RNA polymerase that uses DNA as a template to produce
an RNA fragment that serves as a primer for DNA synthesis.
programmed cell death
A tightly controlled form of cell suicide that allows cells that
are unneeded or unwanted to be eliminated from an adult
or developing organism; the major form is called apoptosis.
prokaryote
Major category of living cells distinguished by the absence
of a nucleus; includes the archaea and the eubacteria
(commonly called bacteria).
prometaphase
Stage of mitosis in which the nuclear envelope breaks down
and duplicated chromosomes are captured by the spindle
microtubules; precedes metaphase.
promoter
DNA sequence that initiates gene transcription; includes
sequences recognized by RNA polymerase and its accessory
proteins.
promoter
DNA sequence that initiates gene transcription; includes
sequences recognized by RNA polymerase and its accessory
proteins.
proofreading
The process by which DNA polymerase corrects its own
errors as it moves along DNA.
prophase
First stage of mitosis, during which the duplicated
chromosomes condense and the mitotic spindle forms.
protease
Enzyme that degrades proteins by hydrolyzing their peptide
bonds.
proteasome
Large protein machine that degrades
proteins that are damaged, misfolded, or no
longer needed by the cell; its target proteins
are marked for destruction primarily by the
attachment of a short chain of ubiquitin.
protein
Macromolecule built from amino acids that provides cells
with their shape and structure and performs most of their
activities.
protein domain
Segment of a polypeptide chain that can fold into a compact,
stable structure and that often carries out a specific function.
protein family
A group of polypeptides that share a similar amino acid
sequence or three-dimensional structure, reflecting a
common evolutionary origin. Individual members often
have related but distinct functions, such as kinases that
phosphorylate different target proteins.
protein kinase
Enzyme that catalyzes the transfer of a phosphate group
from ATP to a specific amino acid side chain on a target
protein.
protein kinase C (PKC)
Enzyme that phosphorylates target proteins in response to
a rise in diacylglycerol and Ca 2+ ions.
protein machine
Assembly of protein molecules that operates as a
cooperative unit to perform a complex series of biological
activities, such as replicating DNA.
protein phosphatase
Enzyme that catalyzes the removal of a phosphate
group from a protein, often with high specificity for the
phosphorylated site.
protein phosphorylation
The covalent addition of a phosphate group to a side chain
of a protein, catalyzed by a protein kinase; serves as a form
of regulation that usually alters the activity or properties of
the target protein.
proteoglycan
Molecule consisting of one or more glycosaminoglycan
chains attached to a core protein; these aggregates can
form gels that regulate the passage of molecules through
the extracellular medium and guide cell migration.
proto-oncogene
Gene that when mutated or overexpressed can transform a
normal cell into a cancerous one.
proton
Positively charged particle found in the nucleus of every
atom; also, another name for a hydrogen ion (H + ).
protozoan
A free-living, nonphotosynthetic, single-celled, motile
eukaryote.
pump
Transporter that uses a source of energy, such as ATP
hydrolysis or sunlight, to actively move a solute across a
membrane against its electrochemical gradient.
purifying selection
Preservation of a specific nucleotide sequence by the
elimination of individuals carrying mutations that interfere
with its functions.
pyruvate
O O –
Three-carbon metabolite that is the end C
product of the glycolytic breakdown of
glucose; provides a crucial link to the
citric acid cycle and many biosynthetic
pathways.
C
CH 3
O
quaternary structure
Complete structure formed by multiple, interacting
polypeptide chains that form a larger protein molecule.
quinone
Small, lipid-soluble, mobile electron carrier molecule that
functions in the respiratory and photosynthetic electrontransport
chains. (See Figure 14–21.)
Rab protein
One of a family of small GTP-binding proteins present on
the surfaces of transport vesicles and organelles that serves