Download APChapter11 2014 - Auburn School District

Cell Communication
AP Biology Chapter 11
Jot down ideas for communication:
You would like to tell your friend across
the room about a party that is happening
tonight, but you don’t want to disrupt your
teacher or let anyone else in class know
about it. How could you get this message
to them before class is over?
Teacher wants to remind everyone in the
class that they have a test on Friday.
What would be the most efficient way to
contact every student?
You are a college counselor [Mr. Mead] at
ARHS and you need to give an application
to all the seniors who are applying for
early admission. How can you notify each
of these people?
You are on the yearbook committee and
would like to organize a fundraising car
wash event. How could you get the word
out to the community, so that there is a
good turnout?
Modes of Communication
How might some of these forms of
communication be similar to how cells
communicate with each other in your body?
Can you think of any examples of short and
long distance messages sent in your body?
Can you think of any cellular messages that
are general information for the whole body
and others that are specific to certain cell?
How can information that is general get to
all the cells in the body efficiently?
An Overview of Cell Signaling
Cell-to-cell communication is essential for
multicellular organisms
The combined effects of multiple signals
determine cell response
Example: the dilation of blood vessels is
controlled by multiple molecules
P207
Cell Communication yeast cells
Cells of the yeast - use chemical signaling to id
cells and to initiate the mating process
1st - cells of mating type A release a-factor, bind
to receptors on nearby cells of mating type B.
B cells release b-factor, which binds to specific
receptors on A cells.
Both "factors" are small proteins – (20 aa)
Binding of these factors to the receptors induces
changes in the cells that lead to their fusion, or
mating.
The resulting A/B cell combines in its nucleus all
the genes from both A and B cells, (diploid).
Bacteria Communication
Prokaryotic example --- p207
The concentration of signaling molecules
allows bacteria to detect population
density
Fig. 11-3
p207
1 Individual rodshaped cells
2 Aggregation in
processegation
in
process
0.5 mm
3 Spore-forming
Spore-forming
structure
(fruiting
body)structur
e
(fruiting body)
Fruiting bodies
Local & Long-distance Signaling
• Cells in a multicellular organism
communicate by chemical messengers
• Animal and plant cells have cell junctions
that directly connect the cytoplasm of
adjacent cells
• In local signaling, animal cells may
communicate by direct contact, or cell-cell
recognition
Fig. 11-4 p208
Plasma membranes
Gap junctions
between animal cells
(a) Cell junctions
(b) Cell-cell recognition
Plasmodesmata
between plant cells
In many other cases, animal cells
communicate using local regulators,
messenger molecules that travel only
short distances
In long-distance signaling, plants and
animals use chemicals called hormones
Fig. 11-3 p190
Long-distance signaling
Local signaling
Target
cell
Secreting
cell
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Endocrine cell
Blood
vessel
Neurotransmitter
diffuses across
synapse
Secretory
vesicle
Hormone travels
in bloodstream
to target cells
Local regulator
diffuses through
extracellular fluid
(a) Paracrine signaling
Target cell
is stimulated
(b) Synaptic signaling
Target
cell
(c) Hormonal signaling
• Communicating cells may be close
together or far apart
• Three stages of cell signaling are:
– Reception
– Transduction
– Response
Figure 11.6 p 209
Communicating cells may be closer
together or far apart
A chemical signal that communicates
between two nearby cells is called a
local regulator. Two types of local
signals have been described in
animals:
–PARACRINE SIGNALING
–SYNAPTIC SIGNALING
Paracrine Signaling
In paracrine signaling, one cell secretes a
signal into the extracellular fluid and the
signal acts on a nearby target cell
Examples of paracrine signaling include
growth factors, which stimulate cells to
grow and divide
Fig. 11-5 p 208
Local signaling
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Target cell
Secreting
cell
Local regulator
diffuses through
extracellular fluid
(a) Paracrine signaling
Neurotransmitter
diffuses across
synapse
Secretory
vesicle
Target cell
is stimulated
(b) Synaptic signaling
Synaptic Signaling
In synaptic signaling, a nerve cell releases
a signal (neurotransmitter) into a synapse,
the narrow space between the transmitting
cell and a target cell, such as another
nerve or muscle cell.
Hormones
A chemical signal which communicates
between cells some distance apart is
called a HORMONE.
Hormones have been described in both
plants and animals
Video Clip #1
Three stages of cell signaling 1/9
Signal reception: The signal binds to a specific
cellular protein called a receptor, which is often
located on the surface of the cell.
Signal transduction: The binding of the signal
changes the receptor in some way, usually a
change in conformation or shape, The change
in the receptor initiates a process of converting
the signal into a specific cellular response; this is
signal transduction.
Cellular response: The transduction system
triggers a specific cellular response. The
response can be almost any cellular
activity…enzyme activation to gene expression!
Fig. 11-6-1
EXTRACELLULAR
FLUID
1 Reception
Receptor
Signaling
molecule
CYTOPLASM
Plasma membrane
Signal Reception and the Initiation
of Transduction
A chemical signal binds to a receptor
protein, causing the protein to change
shape .
The signal molecule is complementary to a
specific region of the receptor protein
The signal behaves as a ligand, a term for
a small molecule that binds to another,
larger molecule
Fig. 11-6-2
CYTOPLASM
EXTRACELLULAR
FLUID
Plasma membrane
1 Reception
2 Transduction
Receptor
Relay molecules in a signal transduction pathway
Signaling
molecule
Signal Reception and the Initiation
of Transduction
Binding of the ligand to the receptor can
lead to the following events:
– Alteration in receptor conformation or shape;
may lead to the activation of the receptor
which enables it to interact with other cellular
molecules
– Aggregation of receptor complexes
Fig. 11-6-3
CYTOPLASM
EXTRACELLULAR
FLUID
Plasma membrane
1 Reception
2 Transduction
3 Response
Receptor
Activation
of cellular
response
Relay molecules in a signal transduction pathway
Signaling
molecule
Signal Receptors
Most signal receptors are plasmamembrane proteins
Many signals molecules cannot pass
freely through the plasma membrane. The
receptors for such signal molecules are
located on the plasma membrane.
p211
GDP and GTP
The function of the G-protein is influenced by the
nucleotide to which it is bound:
– G-proteins bound to GDP are inactive
– G-proteins bound to GTP are active
When a ligand (signal) binds to a G-proteinlinked receptor, the receptor changes its shape
and interacts with a G-protein. This interaction
causes the GDP bound to the inactive G-protein
to be displaced by GTP, thereby activating the
G-protein
GTPase hydrolyses the bound GTP back to
GDP
Video clip #2
p211
Tyrosine-kinase receptors – p212
The structure of a tyrosine-kinase receptor
is characterized by an extracellular ligandbinding domain and a cytosolic domain
These enzymes help control factors such
as cell-cycle control systems
Ion-channel receptors p213
Some chemical signals bind to ligandgated ion channels.
These are protein pores in the membrane
that open or close in response to a ligand
binding, allowing or blocking the flow of
specific ion (Na+, Ca2).
Signal Transduction Pathways
Pathways relay signals from receptors to cellular
responses
Ligand binding to a receptor triggers the first
step in the chain of reactions—the signal
transduction pathway—that leads to the
conversion of the signal to a specific cellular
response
The transduction system does not physically
pass along the signal molecule, rather the
information is passed along. At each step in the
process, the nature of the information is
converted, or transduced into a different form.
Signal Transduction Pathways
Protein phosphorylation is a major
mechanism of signal transduction
Protein phosphorylation the transferring of
a phosphate group from ATP to a protein
substrate (catalyzed by protein kinases).
Cells turn off signal transduction pathways
when the initial signal is no longer present.
Figure 11.10
Signaling molecule
Receptor
Activated relay
molecule
Inactive
protein kinase
1
Active
protein
kinase
1
Inactive
protein kinase
2
ATP
ADP
P
Active
protein
kinase
2
PP
Pi
Inactive
protein kinase
3
ATP
ADP
Pi
Active
protein
kinase
3
PP
Inactive
protein
ATP
PP
Pi
P
P
ADP
Active
protein
Cellular
response
Small Molecules and Ions
Not all the components of signal
transduction pathways are proteins, some
rely on small, nonprotein water soluble
molecules or ions. These are called
second messengers.
Calcium Ions
Many signaling molecules induce their
specific responses in target cells by
increasing the cytoplasm’s concentration
of Ca2+.
The Ca2+ pool can affect signal
transduction by affecting the activity or
function of target proteins
The Ca2+ can bind to relay proteins and
changing the relayed message
Cellular Responses to Signals
In response to a signal, a cell may regulate
activities in the cytoplasm or transcription in the
nucleus
In the cytoplasm, the signaling can affect the
function or activity of proteins which carry out
various processes:
–
–
–
–
Rearrangement of cytoskeleton
Opening or closing of an ion channel
Serve at key points in metabolic pathways
Modulate every aspect of gene expression
Signal Amplification
The production of second messengers
provides a built-in means of signal
amplification.
The binding of one ligand (first message)
can lead to the production of many second
messages.
The degree of amplification is heightened
when the second messenger system is
linked to a phosphorylation cascade.
Signal Specificity
Only target cells with the appropriate receptor
bind to a particular signaling molecule
However, a particular signal can bind to
different cell types and result in different
responses in each of the cell types.
11.5 p223
Apoptosis pp