Transcript Cell-signaling

Cell Communication
Chapter 11
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Trillions of cells in multicellular organisms
must communicate with each other to
coordinate their activities.
In unicellular organisms signaling is important
in finding different mating types for sexual
reproduction.
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Inside the cells there are a
series of chemical changes
that cause the response.
This series of chemical
events that occur is called
the
signal- transduction pathway.
These pathways are common to both humans and
yeast cells suggesting that this strategy evolved
very early on.
LOCAL Signaling
Description –Cell secreting a chemical that acts
on a nearby target cell
Example:
1.
Panacrine signaling
(Growth factors) – compounds
that stimulate nearby cells
to grow and divide
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LOCAL Signaling
Description –Cell secreting a chemical that
acts on a nearby target cell
Example:
2. Synaptic signaling - Neurons secrete
neurotransmitters that diffuse across an
intercellular space (synapse) and interacts
with a another neuron.
Long-Distance Signaling
Description –Use of hormones
(is a chemical secreted by one cell
but exerts is effect on another
cell some distance away).
Example:
1.
Animal Cells - hormone is released into the
vessels of circulatory system and the
molecules travel to target cells.
2. Plant Cells - hormones may travel in vessels or
diffuse the air as a gas.
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Types of Animal Hormones
Modified amino acids- i.e. epinephrine is a modified tyrosine.
Proteins-i.e. insulin is a large protein
Steroid Hormones- i.e. testosterone and estrogen are steroids.
Pheromones are chemicals secreted by one animal to affect
the behavior of another animal.
Direct Contact Signaling
Description –Cells have cell junctions where
direct contact of the cytoplasms of adjacent
cells occur. This allows for signaling substances
in the cytosol to pass feely between the adjacent
cells.
Example:
1.
Animal Cells - communicate via direct contact
between molecule on their surface of their
cell membranes.
2. Plant Cells – Between plasmodesmata.
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The three stages of cell signaling are:
1. Reception
2. Transduction
3. Response
Signal begins when signal interacts with a receptor
site located on the outside surface of the plasma
membrane
Signal is a ____Ligand_
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When the ligand (signal) attaches it will cause a
change in the shape of the receptor site. Receptors
are usually proteins inserted into the plasma
membrane
Ligands (signals) can be: hormones, neurotransmitters,
or growth factors.
Receptors can be: kinases
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Processing the signal
Protein process the signal
Brings about a cellular response
Extremely
Important
Protein kinases - are proteins that transfer
phosphate groups from ATP to another protein.
(Approximately 1% of all our genes code for various protein kinases)
Cascade effect- one protein kinase will activate
another protein kinase by transferring a
phosphate group on to it
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Transduce signal finally triggers a cellular
response.
Response could be:
-activating an exzyme
- activation of gene in nucleus
- synthesis of protein
Bottom line
– Cell-signaling process helps ensure
that crucial activities occur in the right cells, at the
right time, and in the proper coordination with the
other cells of the organism!!
d. Intracellular receptors-Some
signal receptors are NOT found in
the plasma membrane. Instead they
are dissolved in the cytoplasm. This
means the signal must be lipid
soluble to make into the cytosol.
These signals are usually steroids
hormones, thyroxin, and nitric oxide.
i.e. Testosterone enters the cell and
binds with a receptor protein found
in the cytoplasm. This complex now
moves to the nucleus where is acts a
transcription factor and helps
transcribes certain genes. Only
targeted cells have intracellular
receptors.
Types of cellular responses
1. Ultimately activating an enzyme
2. Synthesis of a particular enzyme or protein
1. Activating an enzyme-
Usually when cAMP, Ca++ or IP3 is activated then it will
interact with a specific enzyme to start the cascading effect.
A biochemical pathway usually has a
cascading effect where one protein kinase
will activate another protein kinase by
transferring a phosphate group on to it.
These protein kinases are extremely
important. Approximately 1% of all our
genes code for various protein kinases.
Protein phosphatase is a protein that will
remove a phosphate group from proteins and
can deactivate a protein kinase.