Chapter 11 Flashcards
One topic cells communicate about is
sex
s. Moreover, animal cells may communicate via direct
contact between membrane-bound cell-surface molecules, a process called
cell-cell recognition This
sort of local signaling is especially important in embryonic
development and the immune response.
In many other cases of local signaling, signaling molecules
are secreted by t
the signaling cell. S
) Paracrine signaling
A (b) signaling cell acts on nearby target cells by secreting molecules of a local regulator (a growth factor, for example)
Synaptic signaling
. A nerve
cell releases neurotransmitter
molecules into a synapse, stimulating the target cell, such as
a muscle or another nerve cell.
ndocrine (hormonal) signaling
Specialized endocrine cells
secrete hormones into body fluids, often blood. Hormones reach
most body cells, but are bound by and affect only some cells
A more specialized type of local signaling called synaptic
signaling occurs in the animal nervous system
An electrical signal along a nerve cell triggers the secretion
of neurotransmitter molecules. These molecules act as
chemical signals, diffusing across the synapse—the narrow
space between the nerve cell and its target cell—triggering
a response in the target cell
Both animals and plants use molecules called hormones
for
long distnace signaling
. In hormonal signaling in animals,
also known as endocrine signaling… what hapens with hormonal signaling in plants?
, specialized cells release hormones, which travel via the circulatory system to other parts
of the body, where they reach target cells that can recognize
and respond to them (Figure 11.5c). Plant hormones (often
called plant growth regulators) sometimes travel in plant vessels
(tubes) but more often reach their targets by moving through
cells or by diffusing through the air as a gas
What happens when a potential target cell is exposed to a
secreted signaling molecule?
The ability of a cell to respond
is determined by whether it has a specific receptor molecule
that can bind to the signaling molecule. The information
conveyed by this binding, the signal, must then be changed
into another form—transduced—inside the cell before the
cell can respond. The remainder of the chapter discusses
this process, primarily as it occurs in animal cells.
Sutherland’s work suggested that the process going
on at the receiving end of a cellular communication can
be dissected into three stages
reception transduction and resposne
1 Reception
Reception is the target cell’s detection of
a signaling molecule coming from outside the cell. A chemical signal is “detected” when the signaling molecule binds
to a receptor protein located at the cell’s surface (or inside
the cell, to be discussed later).
2 Transduction
The binding of the signaling molecule
changes the receptor protein in some way, initiating theprocess of transduction. The transduction stage converts the
signal to a form that can bring about a specific cellular response.
a signal transduction pathway
Transduction sometimes occurs in a single step but more
often requires a sequence of changes in a series of different
molecules—a signal transduction pathway. The molecules in the pathway are often called relay molecules; three
are shown as an example
response
In the third stage of cell signaling, the transduced signal finally triggers a specific cellular response. The
response may be almost any imaginable cellular activity—
such as catalysis by an enzyme (for example, glycogen phosphorylase), rearrangement of the cytoskeleton, or activation
of specific
The cell-signaling process
helps ensure that
t crucial activities like these occur in the
right cells, at the right time, and in proper coordination
with the activities of other cells of the organism. W
expReception of the signal depends
on the receiver
Similarly, the signals emitted by an a mating
type yeast cell are “heard” only by its prospective mates, 훂
cells. In the case of the epinephrine circulating throughout
the bloodstream of the impala in Figure 11.1, the hormone
encounters many types of cells, but only certain target cells
detect and react to the epinephrine molecule. A receptor
protein on or in the target cell allows the cell to “hear” the
signal and respond to it. The signaling molecule is complementary in shape to a specific site on the receptor and
attaches there, like a hand in a glove
he largest family of human cellsurface receptors is
the G protein-coupled receptors (GPCRs).
We can see how cell-surface transmembrane receptors work by looking at three major types:
G protein-coupled
receptors (GPCRs), receptor tyrosine kinases, and ion channel receptors
G protein-coupled receptors vary in the
binding sites for their ligands and also for
different types of G proteins inside the cell.
Nevertheles
GPCR proteins are all remarkably
similar in structure. In fact, they make up a
large family of eukaryotic receptor proteins
with a secondary structure in which the single
polypeptide, represented here in a ribbon
model, has seven transmembrane α helices
(outlined with cylinders and depicted in a row
GPCR-based signaling systems are extremely
widespread and diverse in their functions,
including
roles in embryonic development and
sensory reception. In humans, for example,
vision, smell, and taste depend on GPCRs (see
