BIO 311C Lecture Notes - Lecture 11: Signal Transduction, Plasmodesma, Diglyceride
Ch. 11: Cell Communication
1) Cellular Messaging
a) Cells can signal to each other and interpret the signals they receive from other cells and the environment
i) Signals are most often chemicals
b) The same small set of cell-signaling mechanisms shows up in diverse species and processes
2) Concept 11.1: External signals are converted to responses within the cell
a) Communication among microorganisms provides some insight into how cells send, receive, and respond to
signals
b) Evolution of Cell Signaling
i) The east “aharoes ereisiae has to atig tpes, a ad α
(1) Cells of different mating types locate each other via secreted factors specific to each type
ii) The binding of a mating factor at the cell surface initiates a series of steps called a signal transduction
pathway
(1) Molecular details of signal transduction in yeasts and mammals are very similar.
(2) Signaling molecules likely evolved in prokaryotes and single-celled eukaryotes and were adopted for use
in their multicellular descendants
iii) Cell signaling is critical among prokaryotes
(1) A concentration of signaling molecules allows bacteria to sense local population density in a process
called quorum sensing
(2) An example of quorum sensing is the formation of a biofilm
(a) A biofilm is an aggregation of bacterial cells adhered to a surface
(3) Another example of medical importance is the secretion of toxins by infectious bacteria
(a) Interfering with the signaling pathways used in quorum sensing may be a promising approach as an
alternative to antibiotic treatment
c) Local and Long-Distance Signaling
i) Cells in a multicellular organism communicate via signaling molecules
ii) In local signaling, animal cells may communicate by direct contact
(1) Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells
(a) Signaling substances in the cytosol can pass freely between adjacent cells
(2) In other cases, animal cells communicate using secreted messenger molecules that travel only short
distances
(a) Growth factors, which stimulate nearby target cells to grow and divide, are one class of such local
regulators in animals
(b) This type of local signaling in animals is called paracrine signaling
(3) Synaptic signaling occurs in the animal nervous system when a neurotransmitter is released in response
to an electric signal
(4) Local signaling in plants is not well understood beyond communication between plasmodesmata
iii) In long-distance signaling, plants and animals use chemicals called hormones
(1) Hormonal signaling in animals is called endocrine signaling; specialized cells release hormones, which
travel to target cells via the circulatory system
d) The ability of a cell to respond to a signal depends on whether or not it has a receptor specific to that signal
e) The Three Stages of Cell Signaling: A Preview
i) Earl W. Sutherland and colleagues discovered how the hormone epinephrine acts on cells
ii) Sutherland suggested that cells receiving signals went through three processes
(1) Reception: In reception, the target cell detects a signaling molecule that binds to a receptor protein on
the cell surface
(2) Transduction: In transduction, the binding of the signaling molecule alters the receptor and initiates a
signal transduction pathway; transduction often occurs in a series of steps
(3) Response: In response, the transduced signal triggers a specific response in the target cell
3) Concept 11.2: Reception: A signaling molecule binds to a receptor protein, causing it to change shape
i) The binding between a signal molecule (ligand) and receptor is highly specific
(1) A shape change in a receptor is often the initial transduction of the signal
(2) Most signal receptors are plasma membrane proteins
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