Essential Cell Biology 5th edition

Glossary G:15
as a molecular marker to help ensure that transport vesicles
fuse only with the correct membrane.
Ras
One of a large family of small GTP-binding proteins (the
monomeric GTPases) that helps relay signals from cellsurface
receptors to the nucleus. Many human cancers
contain an overactive mutant form of the protein.
reaction center
In photosynthetic membranes, a protein complex that
contains a special pair of chlorophyll molecules; it performs
the photochemical reactions that convert the energy of
photons (light) into high-energy electrons for transport
down the photosynthetic electron-transport chain.
reading frame
One of the three possible ways in which a set of successive
nucleotide triplets can be translated into protein, depending
on which nucleotide serves as the starting point.
receptor
Protein that recognizes and responds to a specific signal
molecule.
receptor serine/threonine kinase
Enzyme-coupled receptor that phosphorylates target
proteins on serine or threonine.
receptor tyrosine kinase (RTK)
Enzyme-coupled receptor in which the
intracellular domain has a tyrosine kinase
activity, which is activated by ligand
binding to the receptor’s extracellular
domain.
receptor-mediated endocytosis
Mechanism of selective uptake of material by animal cells
in which a macromolecule binds to a receptor in the plasma
membrane and enters the cell in a clathrin-coated vesicle.
recombinant DNA
A DNA molecule that is composed of DNA sequences from
different sources.
redox pair
Two molecules that can be interconverted by the gain or
loss of an electron; for example, NADH and NAD + .
redox potential
A measure of the tendency of a given redox pair to donate
or accept electrons.
redox reaction
A reaction in which electrons are transferred from one
chemical species to another. An oxidation–reduction
reaction.
reduction
Addition of electrons to an atom, as occurs during the
addition of hydrogen to a carbon atom or the removal of
oxygen from it; can also refer to a partial shift of electrons
between atoms linked by a covalent bond.
regulatory DNA sequence
DNA sequence to which a transcription regulator binds to
determine when, where, and in what quantities a gene is to
be transcribed into RNA.
regulatory RNA
RNA molecule that plays a role in controlling gene
expression.
replication fork
Y-shaped junction at the site where DNA is being replicated.
replication origin
Nucleotide sequence at which DNA replication is initiated.
reporter gene
Gene encoding a protein whose activity is easy to monitor
P
P
P
P
P
P
P
P
experimentally; used to study the expression pattern of a
target gene or the localization of its protein product.
respiratory enzyme complex
Set of proteins in the inner mitochondrial membrane that
facilitates the transfer of high-energy electrons from NADH
to water while pumping protons into the intermembrane
space.
resting membrane potential
Voltage difference across the plasma membrane when a
cell is not stimulated.
restriction enzyme
Enzyme that can cleave a
DNA molecule at a specific,
short sequence of nucleotides.
Extensively used in recombinant
DNA technology.
retrotransposon
Type of mobile genetic element that moves by being first
transcribed into an RNA copy that is reconverted to DNA
by reverse transcriptase and inserted elsewhere in the
chromosomes.
retrovirus
RNA-containing virus that replicates in a cell by first
making a double-stranded DNA intermediate that becomes
integrated into the cell’s chromosome.
reverse transcriptase
Enzyme that makes a double-stranded DNA copy from
a single-stranded RNA template molecule. Present in
retroviruses and as part of the transposition machinery of
retrotransposons.
Rho protein family
Family of small, monomeric GTPases that controls the
organization of the actin cytoskeleton.
ribosomal RNA (rRNA)
RNA molecule that forms the structural and catalytic core
of the ribosome.
ribosome
Large macromolecular complex, composed of RNAs and
proteins, that translates a messenger RNA into a polypeptide
chain.
ribozyme
An RNA molecule with catalytic activity.
RNA
Molecule produced by the transcription of DNA; usually
single-stranded, it is a polynucleotide composed of
covalently linked ribonucleotide subunits. Serves a variety
of informational, structural, catalytic, and regulatory
functions in cells.
RNA (ribonucleic acid)
Molecule produced by the transcription of DNA; usually
single-stranded, it is a polynucleotide composed of
covalently linked ribonucleotide subunits. Serves a variety
of informational, structural, catalytic, and regulatory
functions in cells.
RNA capping
The modification of the 5′ end of a maturing RNA transcript
by the addition of an atypical nucleotide.
RNA interference (RNAi)
Cellular mechanism activated by double-stranded RNA
molecules that results in the destruction of RNAs containing
a similar nucleotide sequence. It is widely exploited as an
experimental tool for preventing the expression of selected
genes (gene silencing).
RNA polymerase
Enzyme that catalyzes the synthesis of an RNA molecule
5′
G A A T T C
3′
3′ C T T A A G 5′