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Summary Campbell biology Chapter 9
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Samenvatting H9 campbell biology a global approach tenth edition
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Celbiologie samenvattingHoofdstuk 9 Cellular signaling
9.1
Evolution of cell signaling
There are two sexes, mating cells, of yeast cells, called a and α (figure 9.2). Each type secretes a figure 9.2). Each type secretes a ). Each type secretes a
specific factor that binds to receptors only on the other type of cell. When exposed toe each other’s
mating factors, a pair of cells of opposite type change shape, grow toward each other, and fuse
(figure 9.2). Each type secretes a mate). The new a/αα cell contains all the gene sof both original cells, a combination of genetic
resources that provides advantages to the cell’s descendants, which arise by subsequent cell
divisions.
Once received by the yeast cell surface receptor, a mating signal is changed, or transduced, into a
form that brings a bout the cellular response of mating. This occurs in a series of steps called a signal
transduction pathway. Many such pathways exist in both yeast and animal cells.
Bacterial cells secrete molecules that can be detected by other bacterial cells. Sensing the
concentration of such signaling molecules allows bacetria to monitor the local density of cells, a
phenomenon called quorrum sensing. Quorum sensing allows bacterial populations to coordinate
their behaviors in activities that require a given number of cells acting synchronously. One example is
formation of a biofilm, an aggregation of bacterial cells adhered to a surface.
Local and long-distance signaling
Paracrine signaling is a type of local signaling. Messenger molecules are secreted by the signaling
cell. Some of these travel only short distances; such local regulators influence cells in the vicnity. One
class of local regulators in animals, growth factors, are compounds that stimulate nearby target cells
to grow and divide. Numerous cells can simultaneously receive and respond to the molecules of
gowth factor produced by a single cell in their vicinity.
Synaptic signaling is a more specialized type of local signaling and 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 animal and plants use chemicals called hormones for long-distance signaling. In hormonal
signaling in animals, also known as endocrine signaling, specialized cells release hormone molecules,
which travel via the circulatory system to other parts of the body, here they reach traget cells that
can recognize and respond to the hormones (figure 9.2). Each type secretes a figure 9.5c).
Plant hormones (figure 9.2). Each type secretes a plant growth regulators) sometimes travel in vessels but more often reach their
targets by moving through cells or by diffusing through the air as gas. Hormones vary widely in size
and type, as do local regulators.
The three stages of cell signaling
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.
, 2. Transduction
The transduction stage converts the signal to a form that can bring about a specific cellular response.
Transduction sometimes occurs in a single step but more often requires a sequence of changes in a
series of different molecules (figure 9.2). Each type secretes a a signal transduction pathway).The molecules in the pathway are often
called relay molecules.
3. Response
The transduced signal triggers a specific cellular response. The respnse may be almost any imaginable
cellular activity, such as catalysis by an enzyme, rearrangement of the cytoskeleton, or activation of
specific genes in the nucleus. The cell-signaling process helps ensure that 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.
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