Chapter 11
Cell Communication
Student Version
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Cells can receive signals in several different ways
o ______________________________________ – light
o ______________________________________ – touch
o _________________________________ – hormones **Most Common**
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Cell Signaling Evolved Early in Life – YEAST!
o There are 2 types of yeast, and they identify their mates using chemical signaling

The chemicals they secrets causes ___________________________________________
_______________________________________________________________________
_______________________________________________________________________
o Signal Transduction Pathway  ___________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________

This process evolved way before _____________________________________________
________________________________________________________________________
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Communicating cells may be close together or far apart
o _____________________________ Signaling (CLOSE)

Transmitting cells secrete ______________________________________________,
which influences cells in that vicinity

Example of local regulators: GROWTH FACTORS  ________________________
___________________________________________________________________
___________________________________________________________________
_____________________________________________; called paracrine signaling

Animal Nervous system  more specific; one nerve cells produces
neurotransmitters and sends that signal to only ONE target cell; called
__________ _____________________________________________
o Cells further away from each other:

Hormones  chemicals plants and animals use to signal at greater distances; utilizes the
________________________________ system and __________________________
system in animals; in plants hormones can travel in __________________________ but
usually __________________________________________________________________
o Cells that are in direct contact can also communicate

Animals = gap junctions (signals dissolved in cytosol can pass through using these)
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Plants = plasmodesmata
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In animals, signaling is important in _______________________________________ and
in the _________________________________________
o When a cell receives a signal, it must be recognized by a specific receptor and then the
information it carries must be changed into another form – this is called transduction; once this
happens, then the cell can respond
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Three Stages of Cell Signaling: Reception, Transduction, and Response
o Earl W. Sutherland  investigated how ______________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
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He came up with 3 specific steps in cell signaling:

________________________________ = ________________________________
__________________________________________________________________
__________________________________________________________________

________________________________ = ________________________________
___________________________________________________________________
_______________________________________; may be a series of steps called a
________________________________________________________________

________________________________ = cellular response that is triggered by the
transduced signal
SIGNAL RECEPTION AND THE INITIATION OF TRANSDUCTION
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Signal receptors on the target cells are the key to signaling
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Signal molecules binding to receptor proteins can cause the protein to change shape
o The signal molecule is complementary in shape to the receptor and attaches like a lock and key
o ________________________________ = small molecule that specifically binds to a larger one;
the signal molecule behaves like a ligand in this case
o Ligand binding usually causes ______________________________________________________
______________________________________________________________________________
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Most signal molecules are too big to pass through, but the receptor proteins can be embedded in the
plasma membrane, so it can transmit the signal to the inside of the cell by changing shape or
opening/closing when the signal binds to it
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3 types of membrane receptors:
o 1. G-protein linked receptors:
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Many different types but all have the same basic structure
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If _______________ is bound to the protein = ACTIVE
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If _______________ is bound to the protein = INACTIVE

** GTP is similar to ________, and GDP is similar to _________**

See Figure 11.7 pg. 202 for mechanism of G-protein

______________________ converts the GTP back into GDP so the protein
becomes inactive when the signal is no longer there
o 2. Tyrosine-Kinase Receptors:
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A class of plasma membrane receptors characterized by enzymatic activity
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Receptors for Growth Factors
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Can trigger _______________________________________________________
_____________________________________ at once
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Membrane receptors that attach ___________________________________________
_______________________________________________________________________

See Figure 11.8 pg. 203
o 3. Ion-Channel Receptors
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Open or close in response to a __________________________________________, which
allows _______________________________________________________________
_________________________________________(for example, Na+ or Ca2+)
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
Changes shape when molecules bind to create a channel

Very important in the _____________________________ system
Intracellular Receptors
o Some signal receptors are proteins dissolved in the cytoplasm or nucleus of the cell
o Signals need to be able to cross the ___________________________________________ in
order to get into the cell (usually hydro___________!)

Examples: steroid hormones,____________________________________, ____________
______________________________

These receptors act as transcription factors – which activate transcription of the gene
into _____________
SIGNAL TRANSDUCTION PATHWAYS
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Transduction stage is usually a multistep pathway
o Benefit = a small number of extracellular signal molecules can produce a large cellular response;
signal is amplified by one molecule in the chain transmitting the message to multiple molecules
at the next step, and so on
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Pathways relay signals from the receptors to the cellular response
o The signal starts with the activation of the receptor protein, which then passes the signal to the
next molecule, then to the next, etc.
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Usually the molecules in the pathways are proteins and the signals are brought on by
conformational changes – usually caused by _________________________________
(protein kinases = _________________________________________________________
________________________________________________________________________)

Many of the molecules in the signal transduction pathway are protein kinases that act on
each other to create a “___________________________________________________”
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Protein kinases are EXTREMELY important in animals – involved in the regulation of most
genes
o To turn off the signal pathway when the initial signal is no longer present, _________________
_______________________________________ are used; these remove ___________________
groups from ____________________________ thus inactivating those proteins
o THEREFORE…the activity in a cell depends on the balance between ________________________
_________________________ molecules and _________________________________________
molecules
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Second messengers
o Second messengers = _____________________________________________________________
_______________________________________________________________________________
o Most important second messengers = __________________________ and ______________
o 1. Cyclic AMP (cAMP)
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Adenylyl cyclase = _________________________________________________________
________________________________________________________________________
_________________________________________________________________________
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Overview = the first messenger (the hormone) causes a membrane enzyme to
make cAMP, which broadcasts the signal out to the cytoplasm
o Phosphodiesterase = enzyme that converts cAMP into AMP (inactive), so
once the hormone is gone, the signal stops
o Many hormones can signal the formation of cAMP
o cAMP usually works by activating _______________________________
___________________________________________________________
(___________________/_____________________________ kinase)
o See Figure 11.13 pg. 207
o 2. Calcium Ions
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More widely used as a second messenger than cAMP
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The concentration of Ca2+ is…


Lower in _________________________________________________________
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Higher in _________________________________________________________
Calcium is critical for both plants and animals

Animals = _________________________________________________________
__________________________________________________________________
__________________________________________________________________

Plants = ____________________________________________________________
___________________________________________________________________
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Changes in the Ca2+ levels (usually by release of Ca2+ from the ER) initiates other second
messengers

_______________________________________ = Ca2+ binding protein found in
eukaryotic cells; mediates many calcium-regulated processes by changing
conformation and then binding to other proteins to activate or deactivate them
CELLULAR RESPONSES TO SIGNALS
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Signal transduction pathways lead to ____________________________________________________
___________________________________________________________________________________
o Ex. The response of liver cells to signaling by the hormone ______________________________
helps regulate __________________________________________________________________
o Production of transcription factors (which can switch genes on and off)
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Multi-step pathways have two important benefits:
o 1. ________________________________________________

At each step in the process, the number of activated molecules is greater than the one
before it
o 2. ____________________________________________________________________
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The same signal (ex. Hormone) can produce effects in one cell and not in another, OR it
can activate both, but the cells can respond differently – it all depends on the
_________________________________ that make up the cell

How does a specific signal molecule find its substrate?

Scaffolding proteins = ________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
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See Figure 11.19 pg. 212