Essential Cell Biology 5th edition

G:16 Glossary
from a DNA template using ribonucleoside triphosphate
precursors.
RNA processing
Broad term for the modifications that a precursor mRNA
undergoes as it matures into an mRNA. It typically includes
5′ capping, RNA splicing, and 3′ polyadenylation.
RNA splicing
Process in which intron sequences are excised from RNA
molecules in the nucleus during the formation of a mature
messenger RNA.
RNA transcript
RNA molecule produced by transcription that is
complementary to one strand of DNA.
RNA world
Hypothetical period in Earth’s early history in which lifeforms
were thought to use RNA both to store genetic
information and to catalyze chemical reactions.
RNA-Seq
Sequencing technique used to determine directly the
nucleotide sequence of a collection of RNAs.
rough endoplasmic reticulum
Region of the endoplasmic reticulum
associated with ribosomes and involved in
the synthesis of secreted and membranebound
proteins.
S cyclin
Regulatory protein that helps to launch the S phase of the
cell cycle.
S phase
Period during a eukaryotic cell cycle in which DNA is
synthesized.
S-Cdk
Protein complex whose activity initiates DNA replication;
consists of an S cyclin plus a cyclin-dependent protein
kinase (Cdk).
sarcomere
Highly organized assembly of actin and myosin filaments
that serves as the contractile unit of a myofibril in a muscle
cell.
saturated
Describes an organic molecule that contains a full
complement of hydrogen; in other words, no double or
triple carbon–carbon bonds.
scaffold protein
Protein with multiple binding sites for other macromolecules,
holding them in a way that speeds up their functional
interactions.
secondary structure
Regular local folding pattern of a polymeric molecule. In
proteins, it refers to α helices and β sheets.
secretion
Production and release of a substance from a cell.
secretory vesicle
Membrane-enclosed organelle in which molecules destined
for secretion are stored prior to release.
sequence
The linear order of monomers in a large molecule—for
example, amino acids in a protein or nucleotides in DNA;
encodes information that specifies a macromolecule’s
precise biological function.
serine/threonine kinase
Enzyme that phosphorylates target proteins on serines or
threonines.
sexual reproduction
Mode of reproduction in which the genomes of two
individuals are mixed to produce an individual that is
genetically distinct from its parents.
side chain
Portion of an amino acid not involved in forming peptide
bonds; its chemical identity gives each amino acid unique
properties.
signal sequence
Amino acid sequence that directs a protein to a specific
location in the cell, such as the nucleus or mitochondria.
signal transduction
Conversion of an impulse or stimulus from one physical or
chemical form to another. In cell biology, the process by
which a cell responds to an extracellular signal.
single-nucleotide polymorphism (SNP)
Form of genetic variation in which one portion of the
population differs from another in terms of which nucleotide
is found at a particular position in the genome.
sister chromatid
Copy of a chromosome, produced by DNA replication, that
remains bound to the other copy.
small interfering RNA (siRNA)
Short length of RNA produced from double-stranded RNA
during the process of RNA interference. It base-pairs
with identical sequences in other RNAs, leading to the
inactivation or destruction of the target RNA.
small nuclear RNA (snRNA)
RNA molecule of around 200 nucleotides that participates
in RNA splicing.
SNARE
One of a family of membrane proteins responsible for the
selective fusion of vesicles with a target membrane inside
the cell.
SNP (single-nucleotide polymorphism)
Form of genetic variation in which one portion of the
population differs from another in terms of which nucleotide
is found at a particular position in the genome.
somatic cell
Any cell that forms part of the body of a plant or animal that
is not a germ cell or germ-line precursor.
spindle pole
Centrosome from which microtubules radiate to form the
mitotic spindle.
spliceosome
Large assembly of RNA and protein molecules that splices
introns out of pre-mRNA in the nucleus of eukaryotic cells.
standard free-energy change, ΔG°
The free-energy change measured at a defined concentration,
temperature, and pressure. (See also free-energy change.)
starch
Polysaccharide composed exclusively of glucose units, used
as an energy store in plant cells.
stem cell
Relatively undifferentiated, self-renewing cell that produces
daughter cells that can either differentiate into more
specialized cell types or can retain the developmental
potential of the parent cell.
steroid hormone
Hydrophobic signal molecule related to cholesterol; can
pass through the plasma membrane to interact with
intracellular receptors that affect gene expression in the
target cell. Examples include estrogen and testosterone.