Download 1. Categorize chemical signals in terms of the

Chapter 11 RQ
1.
2.
3.
4.
What is a type of “local signaling” for
cells?
What is communicated through “long
distance” signaling?
What is the first stage of cell signaling?
What is the general term for any small
molecule that binds to a larger one?
1. Categorize chemical signals in terms of the
proximity of the communicating cells.


Local Regulators
Paracrine signaling 
one cell secretes the
signal into
extracellular fluid and
acts on another cell
Synaptic signaling  a
nerve cell releases a
signal into a synapse,
such as another nerve
cell or muscle cell

1.
2.
Hormones
Communicates signals
between cells far
apart; examples:
Plants – ethylene gas
which promotes
ripening
Animals – insulin, a
protein which
regulates blood
glucose levels 
2. Overview the basic elements of a signaling
system of a target cell.
1. Reception  signal binds to a specific
cellular protein called a receptor, often at
the cell’s surface
2.Transduction  the binding changes the
receptor’s conformation which initiates a
process of converting the signal into a
specific cellular response (which may have
1 or more steps)
3. Cellular response  can be almost any
cellular activity, such as activation of an
enzyme or altered gene expression 
3. Describe the nature of a ligand-receptor
interaction and state how such interactions
initiate a signal transduction system.


Ligand  term for a small molecule that
binds to another larger molecule
The signal molecule is complementary to a
specific region of the receptor protein
 the alteration in receptor conformation
or shape can lead to the activation of the
receptor which enables it to interact with
other cellular molecules 
4. Compare and contrast G-protein-linked
receptors, tyrosine-kinase receptors, and
ligand-gated ion channels.
G-protein linked  single polypeptide chain
threaded over membrane
- interacts with a variety of proteins
- hosts metabolic and developmental processes
Tyrosine-kinase  characterized by an
extracellular ligand-binding domain and enzyme
activity
- ligand binding causes aggregation of 2 receptor
units which activates the kinase activity
Ion channels  protein pores in the membrane that
open or close in response to ligand binding,
allowing or blocking the flow of specific ions 
5. Describe how phosphorylation propagates
signal information.




Some phosphorylation results in activation
of the target protein (increasing catalytic
activity)
Some result in inactivation
Protein kinases act on other proteins
(sometimes enzymes) and attach the
phosphate group to serine or threonine
residues
Used in signal paths in the cytoplasm of
the cell 
6. Describe how cAMP (cyclic AMP) is
formed and how it propagates signal
information.
1.
2.
3.
4.
5.
6.
Ligand binds to receptor
Receptor conformation changes; G-protein
complex is activated
Active G-protein activates the enzyme adenylyl
cyclase which is associated with the cytoplasmic
side of the plasma membrane
Adenylyl cyclase converts ATP to cAMP
cAMP binds to and activates a cytoplasmic
enzyme protein kinase A
Protein kinase A propagates the message by
phosphorylating various other proteins that lead
to the cellular response 
7. Describe how the cytoplasmic
concentration of Ca 2+ can be altered and
how this increased pool of Ca 2+ is involved
with signal transduction.

Altered in two ways:
1. Ligand binding to a Ca2+ ion-gated
channel
2. Activation of the inositol
triphosphate (IP3) signaling pathway
- ligand binds, conformation change
- IP3 is created and binds to Ca2+ iongated channels

Continued…

Ca2+ affects the signal transduction
1. Directly  affects the activity or
function of target proteins
2. Indirectly  binds to a relay
protein which in turn alters the
activity of enzymes 
8. Describe how the signal information is
transduced into cellular responses in the
cytoplasm and in the nucleus.


Cytoplasm  affect on the function or
activity of the proteins, including:
- rearrangement of the cytoskeleton
- open/close of an ion channel
- key points in metabolic pathways
Nucleus  affect on synthesis of new
proteins by turning on/off genes
- transcription/translation
- gene expression 
9. Describe how signal amplification is
accomplished in target cells.

The making of second messengers like
cAMP provides some amplification
- this is increased when it is linked to a
phosphorylation cascade
- ex: few epinephrine molecules are
needed to result in millions of glucose
molecules released from glycogen in the
liver 
10. Describe how target cells discriminate
among signals and how the same signal can
elicit multiple cellular responses.


Discriminate  like the enzyme, it is
specific to certain cells and receptors
Multiple responses  depending on the
cell it binds to, the responses can vary
hugely
ex: epinephrine on liver vs cardiac
- liver  induces breakdown of glycogen
- heart  stimulates contraction 
 The end 
“Mothers of teenagers know
why some animals eat their
young.” -unknown