Chapter 11 Cell Communica1on
How does cell singling fuel the desperate flight of an animal?
Evolu&on of Cell Signaling
o Quorum Sensing: A concentra+on of signaling molecules allows bacteria to sense local popula&on density.
o Bacterial cells secrete signaling molecules detectable by other bacterial cells.
o Cell signaling is cri+cal among prokaryotes, especially in condi+ons that make it cri+cal for their survival: (individual
rod-shaped cells form, aggregate, and form spore-forming structure (frui+ng body).
o This type of knowledge allows them to gage and act as a team when condi+ons favor that for survival.
o Prokaryotes can be free but they can also act together and strengthen in # to send out chemicals to one another,
catch these chemicals and sum them up to launch a team behavior.
• Biofilm: an aggrega+on of bacterial cells aEached to a surface by signaling molecules secreted by the cells.
o The biofilm forms only aGer cells have reached a certain density.
o Biofilms provide protec+on to bacterial cells, oGen offering nutri&on from the surface they adhere to.
o Examples of biofilms: Fallen log or leaves in a forest; Film on teeth in the morning.
o Disrup&on: Tooth-brushing and flossing are cri+cal to disrupt biofilms that could cause gum disease.
• Medical Implica&ons of Quorum Sensing:
o Quorum sensing regulates the secre+on of toxins by infec+ous bacteria.
o This regula+on has serious medical implica&ons as some treatments with an+bio+cs do not work due to the
evolu+on of an&bio&c resistance.
o Promising treatments: Disrup+ng toxin produc+on by interfering with the signaling pathways used in quorum
sensing.
Example of Cell Signaling in Yeast Cells
• Yeast (Saccharomyces cerevisiae):
o Cells of yeast S. cerevisiae use secreted factors specific to each
type to iden+fy sexual mates. These yeast cells reproduce sexually.
o Two ma+ng types: a and α.
Ma&ng Factor Binding and Cellular Response in Yeast Cells
• Ma&ng Factor and Receptor Binding:
o Ma+ng factors bind only to receptors on the opposite type of
yeast cell (a or α).
o When exposed to each other’s ma+ng factors, yeast cells of opposite
ma+ng types undergo the following:
Change shape, Grow toward each other, Fuse (mate).
• Forma&on of a New a/α Cell:
o The gene+c combina+on provides advantages to the descendants of
the fused cell, which arise through subsequent cell divisions.
• Species-Specific Ma&ng:
, o The unique match between the ma+ng factor and its receptor ensures that ma+ng occurs only between cells of
the same species of yeast.
Signal Transduc&on Pathway in Yeast Cells
• How Ma&ng Factor Binding Ini&ates a Signal:
o The binding of a ma+ng factor to the yeast cell-surface receptor triggers a series of events known as a signal
transduc&on pathway.
o This pathway includes three major steps:
1. Signal recep&on: The ma+ng factor binds to the receptor on the surface of the cell.
2. Signal transduc&on: A cascade of molecular events is triggered within the cell.
3. Cellular response: The cell responds by ini+a+ng ma&ng.
• Conserva&on of Signal Transduc&on Pathways:
o Many similar pathways exist in the cells of both unicellular and mul&cellular organisms.
o The molecular details of signal transduc+on in yeasts and mammals are similar (early versions of cell-signaling
mechanisms evolved before appearance of mul+cellular organisms).
o
Cell Communica&on in Mul&cellular Organisms
o Cells in mul+cellular organisms communicate using signaling molecules.
- Can target cells that may be adjacent or further away.
Types of Cell Communica&on
1. Direct Contact:
o Eukaryo&c cells can communicate by direct contact, a type of local signaling.
o Many animal and plant cells have cell junc&ons that connect the
cytoplasm of adjacent cells.
§ Signaling substances dissolved in the cytosol can pass
directly between neighboring cells.
o Cell-surface molecule interac&on is another form of direct contact,
important in:
§ Embryonic development.
§ Immune response.
§ Maintaining adult stem cell popula&ons.
2. Local Signaling:
o Involves the secre+on of signaling molecules that travel short distances.
o Local regulators influence nearby cells.
§ Paracrine signaling: A type of local signaling in animals.
§ Growth factors: Compounds that s+mulate
nearby target cells to grow and divide.
§ Mul+ple cells can respond to growth
factors produced by a single cell.
o Synap&c signaling:
§ Specialized form of local signaling found in the nervous system.
§ An electrical signal along a nerve cell (axon) which extends and triggers the secre+on
of neurotransmiUers.
§ NeurotransmiEers diffuse across the synapse (the space between the nerve cell and its target cell),
triggering a response in the target cell.
§ Drugs trea+ng depression, anxiety, PTSD affect this signaling process.
§ When cells gather close together, diffusion of neurotransmiEer happens very rapidly with assistance of a
cleG which is a receptor hat passes on the message form one cell to target cell.
3. Long-Distance Signaling (Hormonal Signaling):
o Involves hormones for signaling across longer distances.
o Endocrine signaling: Specialized cells release hormones that travel through the circulatory system to distant target
cells.
o Hormones in plants:
§ Can travel through cells.
§ Vary widely in size and type.
§ Example:
§ Ethylene: A small hydrocarbon (C₂H₄) that promotes fruit ripening and can diffuse through
airand cell walls.
, § Insulin: A mammalian hormone that regulates blood sugar levels. It is a protein with thousands
of atoms.
Cellular Response to Signaling Molecules
• Receptor Molecules:
o For a cell to respond to a signaling molecule, it must have a specific receptor that can bind to the signaling
molecule.
• Signal Transduc&on:
o AGer binding to the receptor, the signal is converted to another form inside the cell—this process is called signal
transduc&on.
o The transduced signal leads to a cellular response.
What makes a
cell a target
cell?
receptors.
This receptor
must
specifically
bind the
chemical in
ques;on
(green)
This signaling system is self-targe+ng; signaling cell and the target cell
are the same.
o The produc+on and secre+on of an extracellular mediator
By a cell followed by the binding of that mediator to
receptors on the same cell to imitate signal transduc+on.
o The cell releases signaling molecules that bind to
receptors on the same cell.
Signaling molecules: nonpolar or polar
I. Nonpolar signaling molecules cross the plasma membrane and find their receptor inside the cell.
a. The receptor ini+ally can have a different chape and aGer that nonpolar signaling molecule reaches the receptor,
conforma+onal change occurs and func+onal change may occur, either lead to ac+va+on or deac+va+on.
b. Since nonpolar signaling molecules need to go through the plasma membrane before reaching the receptor, such
molecules can also go through nontarget cells. However, they will not be useful since non target cells do not have
the receptors to pass on the informa+on.
II. Polar molecules will find receptor embedded in the plasma membrane, on the surface of the cell.
a. Insulin is an example; due to the hydrophilic nature, they bind to membrane receptors which induces a
conforma+onal change in the receptor and triggers downstream signaling pathways, oGen involving cAMP or
calcium ions to propagate the signal inside the cell.
How does cell singling fuel the desperate flight of an animal?
Evolu&on of Cell Signaling
o Quorum Sensing: A concentra+on of signaling molecules allows bacteria to sense local popula&on density.
o Bacterial cells secrete signaling molecules detectable by other bacterial cells.
o Cell signaling is cri+cal among prokaryotes, especially in condi+ons that make it cri+cal for their survival: (individual
rod-shaped cells form, aggregate, and form spore-forming structure (frui+ng body).
o This type of knowledge allows them to gage and act as a team when condi+ons favor that for survival.
o Prokaryotes can be free but they can also act together and strengthen in # to send out chemicals to one another,
catch these chemicals and sum them up to launch a team behavior.
• Biofilm: an aggrega+on of bacterial cells aEached to a surface by signaling molecules secreted by the cells.
o The biofilm forms only aGer cells have reached a certain density.
o Biofilms provide protec+on to bacterial cells, oGen offering nutri&on from the surface they adhere to.
o Examples of biofilms: Fallen log or leaves in a forest; Film on teeth in the morning.
o Disrup&on: Tooth-brushing and flossing are cri+cal to disrupt biofilms that could cause gum disease.
• Medical Implica&ons of Quorum Sensing:
o Quorum sensing regulates the secre+on of toxins by infec+ous bacteria.
o This regula+on has serious medical implica&ons as some treatments with an+bio+cs do not work due to the
evolu+on of an&bio&c resistance.
o Promising treatments: Disrup+ng toxin produc+on by interfering with the signaling pathways used in quorum
sensing.
Example of Cell Signaling in Yeast Cells
• Yeast (Saccharomyces cerevisiae):
o Cells of yeast S. cerevisiae use secreted factors specific to each
type to iden+fy sexual mates. These yeast cells reproduce sexually.
o Two ma+ng types: a and α.
Ma&ng Factor Binding and Cellular Response in Yeast Cells
• Ma&ng Factor and Receptor Binding:
o Ma+ng factors bind only to receptors on the opposite type of
yeast cell (a or α).
o When exposed to each other’s ma+ng factors, yeast cells of opposite
ma+ng types undergo the following:
Change shape, Grow toward each other, Fuse (mate).
• Forma&on of a New a/α Cell:
o The gene+c combina+on provides advantages to the descendants of
the fused cell, which arise through subsequent cell divisions.
• Species-Specific Ma&ng:
, o The unique match between the ma+ng factor and its receptor ensures that ma+ng occurs only between cells of
the same species of yeast.
Signal Transduc&on Pathway in Yeast Cells
• How Ma&ng Factor Binding Ini&ates a Signal:
o The binding of a ma+ng factor to the yeast cell-surface receptor triggers a series of events known as a signal
transduc&on pathway.
o This pathway includes three major steps:
1. Signal recep&on: The ma+ng factor binds to the receptor on the surface of the cell.
2. Signal transduc&on: A cascade of molecular events is triggered within the cell.
3. Cellular response: The cell responds by ini+a+ng ma&ng.
• Conserva&on of Signal Transduc&on Pathways:
o Many similar pathways exist in the cells of both unicellular and mul&cellular organisms.
o The molecular details of signal transduc+on in yeasts and mammals are similar (early versions of cell-signaling
mechanisms evolved before appearance of mul+cellular organisms).
o
Cell Communica&on in Mul&cellular Organisms
o Cells in mul+cellular organisms communicate using signaling molecules.
- Can target cells that may be adjacent or further away.
Types of Cell Communica&on
1. Direct Contact:
o Eukaryo&c cells can communicate by direct contact, a type of local signaling.
o Many animal and plant cells have cell junc&ons that connect the
cytoplasm of adjacent cells.
§ Signaling substances dissolved in the cytosol can pass
directly between neighboring cells.
o Cell-surface molecule interac&on is another form of direct contact,
important in:
§ Embryonic development.
§ Immune response.
§ Maintaining adult stem cell popula&ons.
2. Local Signaling:
o Involves the secre+on of signaling molecules that travel short distances.
o Local regulators influence nearby cells.
§ Paracrine signaling: A type of local signaling in animals.
§ Growth factors: Compounds that s+mulate
nearby target cells to grow and divide.
§ Mul+ple cells can respond to growth
factors produced by a single cell.
o Synap&c signaling:
§ Specialized form of local signaling found in the nervous system.
§ An electrical signal along a nerve cell (axon) which extends and triggers the secre+on
of neurotransmiUers.
§ NeurotransmiEers diffuse across the synapse (the space between the nerve cell and its target cell),
triggering a response in the target cell.
§ Drugs trea+ng depression, anxiety, PTSD affect this signaling process.
§ When cells gather close together, diffusion of neurotransmiEer happens very rapidly with assistance of a
cleG which is a receptor hat passes on the message form one cell to target cell.
3. Long-Distance Signaling (Hormonal Signaling):
o Involves hormones for signaling across longer distances.
o Endocrine signaling: Specialized cells release hormones that travel through the circulatory system to distant target
cells.
o Hormones in plants:
§ Can travel through cells.
§ Vary widely in size and type.
§ Example:
§ Ethylene: A small hydrocarbon (C₂H₄) that promotes fruit ripening and can diffuse through
airand cell walls.
, § Insulin: A mammalian hormone that regulates blood sugar levels. It is a protein with thousands
of atoms.
Cellular Response to Signaling Molecules
• Receptor Molecules:
o For a cell to respond to a signaling molecule, it must have a specific receptor that can bind to the signaling
molecule.
• Signal Transduc&on:
o AGer binding to the receptor, the signal is converted to another form inside the cell—this process is called signal
transduc&on.
o The transduced signal leads to a cellular response.
What makes a
cell a target
cell?
receptors.
This receptor
must
specifically
bind the
chemical in
ques;on
(green)
This signaling system is self-targe+ng; signaling cell and the target cell
are the same.
o The produc+on and secre+on of an extracellular mediator
By a cell followed by the binding of that mediator to
receptors on the same cell to imitate signal transduc+on.
o The cell releases signaling molecules that bind to
receptors on the same cell.
Signaling molecules: nonpolar or polar
I. Nonpolar signaling molecules cross the plasma membrane and find their receptor inside the cell.
a. The receptor ini+ally can have a different chape and aGer that nonpolar signaling molecule reaches the receptor,
conforma+onal change occurs and func+onal change may occur, either lead to ac+va+on or deac+va+on.
b. Since nonpolar signaling molecules need to go through the plasma membrane before reaching the receptor, such
molecules can also go through nontarget cells. However, they will not be useful since non target cells do not have
the receptors to pass on the informa+on.
II. Polar molecules will find receptor embedded in the plasma membrane, on the surface of the cell.
a. Insulin is an example; due to the hydrophilic nature, they bind to membrane receptors which induces a
conforma+onal change in the receptor and triggers downstream signaling pathways, oGen involving cAMP or
calcium ions to propagate the signal inside the cell.
