Transcript Signal Transduction pt 1

Cells communicate by generating,
transmitting and receiving
chemical signals
CELL COMMUNICATION PROCESSES SHARE
COMMON FEATURES THAT REFLECT A
SHARED EVOLUTIONARY HISTORY
Communication via Transduction
 A signal on a cell’s surface
is converted to a specific
cellular response in a series
of steps
 1st evolved in ancient
prokaryotes and singlecelled eukaryotes
 Quorum Sensing – the
concentration of signaling
molecules allows a bacteria
population to communicate
 http://www.ted.com/talks/
bonnie_bassler_on_how_
bacteria_communicate.ht
ml
 What did you think!??!

AMAZING – right?
 This communication allows
for the evolution of the
bacterial species

With this communication
prokaryotes have adapted
and survived for millions of
years!
Communication via
Transduction
IN MULTICELLULAR ORGANISMS, SIGNAL
TRANSDUCTION PATHWAYS COORDINATE
THE ACTIVITIES WITHIN INDIVIDUAL CELLS
THAT SUPPORT THE FUNCTION OF THE
ORGANISMS AS A WHOLE.
Local vs. Long-Distance Signaling
 Local:
 Cell junctions – substances
dissolved in cytosol pass
through cell to cell
connection (gap junctions &
plasmodesmata)
 Cell-cell Recognition –
interaction between
molecules protruding from
cell surface (i.e. immune
response)
 Local Regulators – signaling
cells secrete messenger
molecules that stimulate or
inhibit nearby cells (growth
factors and
neurotransmitters)
 Long-Distance
 Endocrine signaling –
specialized cells release
hormones that travel
through the blood stream to
target cells in other parts of
the body; plant regulators
move through cells or diffuse
through the air as a gas
 Transmission signaling of
the nervous system –
electrochemical signals travel
long distances by passing
from nerve cell to nerve cell
until the target cells is
reached.
Illustrative Example: Epinephrine
stimulation of glycogen breakdown
in mammals
EPINEPHRINE IS SECRETED BY THE
ADRENAL GLAND DURING TIMES OF MENTAL
AND PHYSICAL STRESS.
2. EPINEPHRINE TRAVELS VIA THE
BLOODSTREAM TO MUSCLE CELLS.
3. WHEN EPINEPHRINE COMES IN CONTACT
WITH THE CELL IT TRIGGERS A SIGNAL
TRANSDUCTION PATHWAY THAT ACTIVATES
GLYCOGEN PHOSPHORYLASE
4. GLYCOGEN PHOPHORYLASE THEN BEGINS
THE BREAKDOWN OF GLYCOGEN TO
GLUCOSE-6-PHOSPHATE WHICH CAN ENTER
GLYCOLYSIS OR CAN BE MODIFIED TO ENTER
THE BLOOD STREAM TO FUEL OTHER CELLS
1.
Signal
Transduction
Pathway
1.
Reception – signal
molecule detected
by target cell
2.
Transduction binding of signal
molecule modifies
receptor protein
initiating a series of
reactions that relay
the message
3.
Response – signal
triggers specific
cellular response
Signaling Molecules
 Ligand – signal molecule that binds to receptors; the
molecule that starts a signal transduction pathway
 Example: Insulin binds to a receptor (integral membrane
protein) causing a change in the protein shape that
exposes a kinase (phosphate transferring enzyme) inside
a cell; the activated kinase transfers the phosphate to
adjacent receptor molecules, leading to the activation of
subcellular proteins and a cellular response to insulin
 Different receptors recognize different chemical
messengers, which can be peptides, small chemicals or
proteins, in a specific one-to-one relationship
Receptor Molecules
 Receptor molecules – integral membrane proteins
that pass through the lipid bilayer transmit
information from the extracellular environment to
the inside of the cell by changing shape
 A receptor protein recognizes signal molecules
(ligands), causing the receptor protein’s shape to
change, which initiates transduction of the signal
G Protein-Coupled Receptors
 G protein-coupled receptors
work with energy rich GTP
to change shape upon
binding with ligand;
common across many
species showing
evolutionary significance
 Important in embryonic
development and sensory
reception
 Key role in many human
illnesses – bacterial
infections interfere with Gprotein function
Tyrosine Kinase
 Tyrosine Kinases are enzymes




that catalyze the
phosphorylation of tyrosine
Upon activation by the ligand
the kinase transfers a
phosphate from ATP to
tyrosine
Phosphorylation of tyrosine
triggers a cascade of reactions
within the cell leading to a
desired response
One receptor can activate ten or
more pathways / cellular
response at once
Important in regulating cell
growth and reproduction
Ion Channel Receptors
 Ion channel Receptors – part of
the receptor acts as a gate,
blocking transfer of ions
 Upon activation by the ligand
the gate opens to allow the flow
of specific ions
 Important for the nervous
system – gated ion channels on
receiving cells cause channels
to open allowing
neurotransmitters to trigger an
electrical signal (some gates
controlled by electrical signals
instead of ligand = voltagegated ions channels)